A & P - Clinical Applications

Kidney Failure: Low Potassium

A 16-year-old cat has kidney failure. One of the findings on the serum chemistry test is a low serum potassium concentration. Potassium (K) is an electrolyte that is important for muscle contraction and nerve function. The low level of potassium is caused by the cat's lack of appetite over the last few weeks: kidney disease makes the cat feel nauseated, so she has a reduced intake of potassium-containing foods and loss of potassium through the damaged kidneys. The lack of potassium makes her feel weak, and it can slow her gastrointestinal contractions and cause constipation. More dangerously, because potassium plays an important role in muscle contraction, the low potassium makes it difficult for the heart muscle to contract. This reduces blood flow to the tissues and can also cause irregular heartbeat; these arrhythmias can be life threatening. We treat this condition by supplementing her intravenous fluids with potassium or by giving her oral potassium supplements.

Cataracts

A cataract is an abnormal condition of the eye whereby the lens becomes opaque. Instead of having a normal transparent appearance, a cataract lens appears milky. This impairs vision, particularly in dim light. Cataracts can be a normal part of the aging process. As a result, they are often seen in older animals, in which they can lead to total or near-total blindness. In younger animals, they can be genetically inherited or develop secondary to conditions such as infection, trauma, diabetes mellitus, or excessive exposure of the eyes to ionizing radiation (such as x-rays). Usually the only effective treatment for a cataract is surgical removal of the affected lens.

Ketosis and Eclampsia: The Importance of Carbohydrates

We know how important carbohydrates are in providing animals with adequate energy levels. We also know how profoundly sensitive the brain is to even small decreases in blood glucose levels. For herbivores, the consumption of sufficient amounts of starch and cellulose from plants plays a vital role in their management, particularly if they are pregnant. The nutritional requirements in the first two trimesters of pregnancy are close to those needed for maintenance during the nonpregnant state. However, in the last trimester and during lactation, nutritional demands increase dramatically. Energy requirements are proportional to the number of fetuses and are highest during lactation. Thus, cows carrying twins and ewes carrying twins or triplets have the highest nutritional needs. Serious metabolic disease can occur if the nutrition to these pregnant or lactating animals is interrupted. When pregnant ewes and cows receive inadequate nutrition, their bodies will compensate for the caloric deficiency by metabolizing their own tissues, primarily their fat reserves. Ketones are formed from the breakdown of the tissue and are released into the bloodstream, called ketonemia, and into the urine, called ketonuria. Even the breath of the animal contains ketones, and it therefore smells like acetone or nail polish remover. This condition is called ketosis. Ketosis is considered primary if the animal is fed an insufficient or unpalatable diet. It is called secondary ketosis if the animal is provided adequate nutrition but stops eating because of an illness, such as mastitis or metritis. Left abomasum displacement is the primary cause of secondary ketosis in cows. In both primary and secondary ketosis, the cow or ewe is not able to supply enough glucose from the digestion of food or from the catabolism of tissues to meet the needs of the developing fetuses or lactation and her own needs. When ketosis occurs in preparturient, or pregnant, cows and ewes, it may precipitate a dangerous and often fatal metabolic disorder known as eclampsia. The primary sign is hypoglycemic encephalopathy, because the brain is adversely affected by the extremely low glucose level. The illness lasts 2 to 5 days. Affected animals are usually fat, as a result of overfeeding in the early part of gestation, but subsequently consume inadequate nutrition during the last trimester. Initially they are often restless and uncoordinated, as though drunk; later, they become listless, anorexic, and they walk aimlessly, sometimes bumping into things because of a condition known as cortical blindness. They may grind their teeth, develop unusual postures, and may exhibit muscle twitching on the face and ears. Finally, the animals become sternally recumbent, develop rapid, weak pulses; and do not get up. Coma and death often follow, and mortality is about 80%. Not surprisingly, blood tests show high ketone and low glucose levels. Guinea pigs, ferrets, and rabbits are also predisposed to developing eclampsia. Postparturient ketosis usually appears a few days to weeks after giving birth, when milk production is high. Lactation requires huge amounts of glucose to make lactose for milk. When inadequate carbohydrates are consumed, glycogen stores in the liver are used first. The metabolism of tissues, which promotes ketogenesis, soon follows once the glycogen stores have been depleted. Clinical signs of postparturient ketosis include depression, lethargy, a staring expression, decreased milk production, weight loss, and a humped-back appearance consistent with abdominal pain. Occasionally, postparturient ketosis will cause frenzied behavior, such as circling, staggering, bellowing, head pressing, and compulsive walking, which occurs for about an hour. As with all ketotic states, ketones are present in the blood, urine, and breath, and there is a marked decrease in blood glucose levels. Unlike eclampsia, however, postparturient ketosis is self-limiting, because the reduction of food intake eventually causes milk production and the corresponding glucose drain to stop. By far the best and least expensive treatment for ketosis is prevention. Providing fresh, palatable feed in appropriate quantities at the appropriate times is the key to a successful breeding program.

Multiple Sclerosis

Multiple sclerosis, also known as MS, is a disease of humans that results in damage to the myelin sheaths of nerve fibers in the brain and spinal cord. Nerve fibers whose myelin sheaths have been damaged conduct impulses abnormally, or not at all. Because both sensory and motor nerve fibers can be affected, the clinical signs of MS can be sensory and/or motor. Sensory effects include tingling, numbness, visual problems, and difficulties with coordination and balance. Motor effects include muscle weakness, muscle spasms, difficulty moving, and problems with speech and swallowing. The exact cause of MS is not known, but it is believed to be caused, at least in part, by the person's own immune system attacking the nervous system.

Myasthenia Gravis

Myasthenia gravis interferes with normal skeletal muscle function and movement. It is an autoimmune disease in which antibodies target the receptors for acetylcholine, preventing the transmission of nerve impulses to the skeletal muscle, thereby preventing contraction. Given that the dog's esophagus consists of skeletal muscle throughout, myasthenia gravis causes a loss of muscle tone in the esophagus, resulting in an esophageal dilation termed megaesophagus. Food is not properly moved down the esophagus and the dog presents with a history of regurgitation of undigested food. Owners often mistake regurgitation for vomiting. Regurgitation does not involve the profound muscular contractions associated with vomiting. With regurgitation, the food coming up is not digested because it has not yet reached the stomach. Animals with megaesophagus are fed in a position where the head is elevated to allow gravity to assist movement of food into the stomach. Animals with megaesophagus are more prone to aspirating food into the lungs so they must be monitored for signs of aspiration pneumonia.

Conjunctivitis

Conjunctivitis is inflammation of the conjunctiva of the eye. It is one of the most common eye diseases and occurs in all common domestic animal species. Signs include redness (hyperemia) and swelling (chemosis) of the conjunctiva, accompanied by ocular discharge and discomfort. The ocular discharge seen with conjunctivitis can range from watery (serous) to bloody (sanguineous) or pus-like (purulent). Causes include bacterial and viral infections, as well as physical and chemical irritants. Conjunctivitis is often seen in dogs that have been swimming in pools containing chlorinated water or hanging their heads out of car windows. Often the precise cause (etiologic factor) is not known. In mild cases of conjunctivitis, medical treatment may not be necessary. In more severe cases, antibiotic ointments or drops, which often contain corticosteroids to lessen the inflammation, are administered topically. Most cases of conjunctivitis respond well to treatment.

Neutrophilia and Leukocytosis

If there is an increased demand for neutrophils in tissue, bone marrow will release its reserve stores of mature—and, if necessary, immature—neutrophils into blood, so they can be transported to the site where neutrophils are needed. If a blood sample is drawn while these neutrophils are in transit, there will be a higher than normal number of neutrophils in the sample. This is called neutrophilia, and it is usually detected on a differential cell count. The increased number of neutrophils will also increase the total number of white blood cells in the sample. This is called leukocytosis and usually is detected using an automated blood analyzer or by looking at the thickness of the buffy coat in a hematocrit tube. Leukocytosis with accompanying neutrophilia can indicate an infection somewhere in the body.

Swollen Lymph Nodes

If there is an infection in some part of the body, the microorganism to blame may be picked up by a lymph vessel and carried to a lymph node. As the lymph passes through the lymph node, the tissue macrophages will attempt to remove the microorganisms. As the macrophages get more active, the lymph node becomes larger as a result of the multiplication of lymphocytes and the arrival of more macrophages. Some lymph nodes are located close to the surface of the body and can be palpated (felt) through the skin. If they are responding to an infection in their drainage area, they will become larger and be more readily palpated. If enlarged, lymph nodes can be used as a clue to the location of an infection. You may be familiar with the mandibular lymph nodes located just behind each side of your jaw in your neck region. These are the "glands" that swell when you have a cold. This is because the mandibular lymph nodes (they are not true glands) drain the nasal cavity, mouth, and pharynx.

What is Mange Anyway?

Mange is an inflammation of the dermis and epidermis (dermatitis) caused by tiny mites that live on or in the skin. The mites cause irritation, itchiness (pruritus), and hair loss (alopecia). Animals often rub and scratch themselves to the point of causing deep scratches in their skin (excoriations), which ooze serum and blood. The skin thickens (hyperkeratosis) and becomes flaky. Bloody exudates from vigorous scratching harden and form crusts, making the swollen red integument vulnerable to secondary bacterial infection (pyoderma). The distribution of the red, hairless patches and the way in which the mange spreads depend on the species of the host and the type of mite involved. The type of mange can be identified by scraping the skin with a dull scalpel blade, transferring the scrapings to a microscope slide, and examining the slide under a microscope. Mites that live in the hair follicles and sebaceous glands are called Demodex. These are long, thin mites with short stubby legs. Demodex are normally found in small numbers on many mammals, but in young or immunosuppressed animals the population of mites can go unchecked and increase to abnormal levels, causing visible patches of hair loss. Infestations of Sarcoptes mites are particularly itchy, because they like to burrow into the oozing excoriations of the skin. In contrast to Demodex, Sarcoptes mites have round bodies. They are drawn initially to areas that are relatively hairless such as the edges of the ears and elbow caps. From these locations, the mange spreads in dogs onto the face, neck, and up and down the legs. Sarcoptic mange is agonizingly itchy, and affected dogs are often miserable and unable to sleep. Sarcoptes scabiei is the species of mite that causes scabies or mange in people, dogs, foxes, horses, and cattle. Notoedres is the mite most commonly linked to mange in cats, rats, and rabbits. It looks and behaves like Sarcoptes but is smaller. It often begins on the ears in cats, then spreads over the face, to the paws during grooming, and then to the hind legs because of the position the animal assumes when sleeping. Because mites can spread from humans to other animals and from animals to humans, it is important to identify the mite involved in the infestation correctly. Performing a skin scraping is essential in any suspected mange case. For example, Mimi was a 3-year-old, female spayed domestic shorthair cat. Her owner brought her to the clinic because of hair loss on Mimi's face. The hair loss had occurred progressively during the previous 3 weeks and was getting worse. Given the species of the host (felid) and the location of the alopecia, Notoedres cati was high on the list of probable causes for the hair loss; however, when a skin scraping was performed, Mimi had scabies, not Notoedres. When the owner was asked if she had any red, itchy rashes, she pulled up her shirt to show a rash under the waistband of her pants. It was later shown that the woman had infected the cat, not the other way around.

Cryptorchidism

Sometimes one or both of the testes do not descend into the scrotum. This is referred to as cryptorchidism. This condition can be either unilateral, when one testis has failed to descend, or bilateral, when both testes have failed to descend. An undescended testis can be located anywhere along the normal path of descent, from the region of the kidney to an area just outside the inguinal ring but not completely down in the scrotum (called a "high flanker"). Testes retained in the abdominal cavity are usually sterile (cannot produce spermatozoa) because spermatogenesis requires a temperature slightly lower than body temperature. The interior of the abdomen is too hot for spermatozoa to be produced. However, testosterone continues to be produced, so a bilaterally cryptorchid animal has all the characteristics of a male animal but typically cannot reproduce.

Wobbler Syndrome

Wobbler syndrome occurs most commonly in certain breeds of dog—Basset Hounds, Borzois, Doberman Pinschers, and Great Danes—and horses, particularly Thoroughbreds. It results from a narrowing of the spinal canal in the cervical region that compresses the spinal cord. This narrowing can result from physical abnormalities (malformations) of cervical vertebrae or improper joints (malarticulations) between them. The precise cause is not known, but inherited factors and nutritional factors seem to be involved. Clinical signs typically develop slowly and gradually, starting with weakness and incoordination, called ataxia. The name wobbler syndrome comes from the wobbly, uncoordinated gait seen in affected animals, and the disease can progress to complete paralysis. Medical treatments may be attempted to decrease the compression of the spinal cord, but surgery is often necessary. The prognosis for recovery is usually guarded at best.

Starvation: A Life and Death Issue

We have all marveled at the fortitude of wild animals that survive severe winters, drought, and food deprivation. Neglected domestic animals may also endure inadequate shelter, food supplies, and access to water. For them, food deprivation and subsequent starvation are a threat to their lives. Fortunately, evolution has dictated physiologic adaptations that extend the time animals can live without food. Except for the terminal phase, starvation is reversible, and the reproductive capacity of the animal is preserved for as long as possible. How does the body do this? The process of starvation can be organized into three stages. Stage I Initially, the body tries to balance the animal's energy expenditure with energy intake by lowering the basal metabolic rate. In this way, the animal needs less food for maintenance but may feel weak, dizzy, and tired. Although many tissues can use nutrients other than glucose, certain tissues—such as blood cells, the kidney, and nervous tissue (brain and spinal cord)—are normally glucose dependent. The body, therefore, uses glycogen stores in the liver to provide glucose to these important tissues. However, the glycogen stores are depleted after several hours, and the body must turn to other sources of energy. Glycerol and fatty acid stores from fat and amino acids from body proteins are catabolized next to produce glucose. Ketone bodies are released as a product of fatty acid metabolism, causing the blood levels of ketone bodies and glucose to rise. Stage II After 1 to 2 weeks, depending on the species, a change occurs in the body that allows the brain and other tissues to use ketones and glucose for energy. Stored body fat becomes the primary source of energy as the body breaks down fatty acids into ketone bodies. This process continues until fat reserves are depleted. The length of this stage varies among individual animals, depending on the amount of body fat that is available for catabolism. Generally, this stage lasts for several weeks. Because body fat serves primarily as an energy storage tissue, an insulator, and protector of internal organs, progressive loss of adipose tissue does not threaten normal body functions or survivability until the stores are nearly depleted. Stage III Once fat reserves are used up, protein becomes the principal metabolic fuel. Even during the first stages of starvation, the body catabolizes protein to produce glucose. However, the level of protein catabolism remains high after the fat reserves are depleted. Initially, liver and plasma proteins are used, followed by protein from the gastrointestinal tract, heart, and skeletal muscle. These structures decrease dramatically in size, and critical body functions are lost. Decreases in plasma proteins, for example, lead to changes in oncotic pressure, and fluid subsequently leaks into the abdominal cavity, causing abnormal distention called ascites. Loss of muscle between ribs and in the diaphragm may lead to respiratory failure. The heart, which can lose 50% of its mass, may simply stop beating. Gastric emptying and intestinal transit times are prolonged, and the absorption of fat and protein is impaired as the inner layers of the intestine degenerate. Diarrhea and nausea may result. In addition, malnourished animals are immunocompromised and often develop pneumonia and other infections. Only the skeletal system seems remarkably unaffected by starvation. Treatment Warm, intravenous fluids in conjunction with antibiotics and parenteral nutrition are important in the treatment of end-stage starvation. In addition, malnourished animals are less able to maintain adequate body temperature and should be given a warm environment in which to recover. Good nursing care is important in these cases, because animals will need thick, soft bedding and care for any decubital ulcers or sores that may have developed from prolonged recumbency. After the animal has been stabilized through the use of parenteral nutrition, high-protein liquid diets should be given by mouth initially until semisolid foods can be tolerated.

Feline Chronic Renal Failure

A 12-year-old male castrated, domestic shorthair cat named "Magic" is presented for lethargy, anorexia, and vomiting. After taking a thorough history, the veterinary technician learns that the cat has had a decreased appetite for 1 to 2 months and has been uncharacteristically reclusive and hides under the bed much of the time. The cat has also vomited several times in the past 2 weeks. On physical examination, the veterinary technician finds Magic to be quiet, alert, and responsive (QAR) with multiple mats in his coat. His temperature is 100.2° F (37.89° C), pulse 180 beats per minute, and respiratory rate 38 breaths per minute. Mucous membranes are pale pink and tacky, with a capillary refill time (CRT) of 2 to 3 seconds.The veterinary technician finds a small oral ulcer and estimates Magic's body condition score (BCS) to be 2 out of 5. When Magic's current weight is compared with his weight 8 months ago, it is discovered that he has lost 1.2 lb. When the skin over the neck is tented, the tent persists longer than normal. Little to no urine is palpable in the urinary bladder. Based on her physical examination findings, the veterinary technician makes the following technician evaluations: • Hypovolemia (tacky mucous membranes) • Decreased perfusion (delayed CRT) • Inappropriate elimination (little urine production) • Vomiting and nausea • Exercise intolerance (lethargy) • Abnormal eating behavior (anorexia) • Underweight (2/5 BCS) • Self-care deficit (matted fur) • Altered mentation (reclusive) • Altered oral health (mucous membrane ulceration) The veterinary technician alerts the veterinarian to her findings and readies the materials needed for venipuncture and urine collection. After examining the cat, the veterinarian orders a complete blood count (CBC), blood chemistry, and urinalysis. The veterinary technician draws blood from the jugular vein and obtains urine via cystocentesis. Using the in-clinic laboratory equipment, the veterinary technician completes the blood tests and urinalysis ordered by the veterinarian.The CBC results reveal a decreased packed cell volume (PCV) and an increased total protein (TP). Blood chemistry shows a significantly increased blood urea nitrogen (BUN) and creatinine. Urinalysis results reveal a urine specific gravity of 1.010 and proteinuria. The lab results, along with a 1- to 2-month history of clinical signs, lead the veterinarian to conclude that Magic is in chronic renal failure, and promptly meets with the owner to discuss the seriousness of his condition. Rationale for the Veterinary Diagnosis All of the abnormalities seen on physical examination and analyses of the patient's blood and urine can be attributed to a lack of normal kidney function. Here's why.... 1. The decreased production of red blood cells, which gives rise to a diminished PCV, is due to the lack of erythropoietin, a hormone normally produced by the kidney. 2. As kidney function fails, the mechanisms that concentrate urine no longer function properly and excessive water is lost in urine, leading to dehydration. Dehydration is manifest as lethargy, decreased blood pressure, and decreased perfusion of tissues. It is also associated with an elevation in PCV and an isosthenuric specific gravity of urine. Both findings are strong indicators that Magic's kidneys are no longer able to concentrate urine. 3. Elevations of physiologic waste products, both BUN and creatinine, occur as the weakened kidneys fail to remove them. The buildup of these compounds in blood is responsible for the symptoms of nausea, vomiting, and anorexia seen commonly in cases of renal failure. 4. The presence of large molecules, such as protein, in the urine is a result of damage to the delicate filtration membranes in the glomerulus. Questions to Consider Before Treatment is Started • What are the goals of treating a patient with chronic renal failure? • How will Magic's dehydration be addressed, both in the hospital and potentially at home? • How can urine output be monitored while Magic is hospitalized? • How will the clinical signs of renal failure be managed (vomiting, lethargy, anorexia) to improve Magic's quality of life? Treatment Magic is admitted to the hospital in an effort to slow the progression of his renal failure and to control the clinical signs of the disease. An intravenous catheter is placed in his cephalic vein and intravenous fluids are administered to replace Magic's fluid losses and to meet his ongoing needs for fluids (see figure). A urinary catheter is placed and is connected to a urine collection system so that urine production can be monitored. Medications are also administered to help control the clinical signs of renal failure such as anorexia, vomiting, and anemia. Magic will be hospitalized for several days with the goals of rehydrating him, flushing some of the built-up waste products from his body, and controlling his clinical signs. If blood work results show an improvement in his condition, Magic may be able to continue treatment at home. With home care, he may have several more months of quality time with his owner.

Urinalysis

A urinalysis ("UA") is the laboratory analysis of a urine sample. It can be performed by a commercial laboratory or by veterinary personnel within a veterinary clinic. Performing a complete urinalysis involves three major steps: 1. A gross examination of the physical properties of the sample. 2. A chemical analysis of substances dissolved in the urine. 3. A microscopic examination of the solid components in the urine. Before beginning a urinalysis, a urine sample must be obtained from the patient. There are several options for urine collection. Ideally, the sample should be collected in a sterile manner so that any bacteria observed in the sample are derived from the urinary tract and not from contamination of the sample during collection. Sterile collection methods include urinary catheterization or cystocentesis. To perform cystocentesis (A), a sterile needle is inserted through the skin of the lower abdomen and into the bladder. Urine is drawn directly from the bladder through the needle and into the sterile syringe. Nonsterile methods of sample collection include "catching" the urine in a container as it is voided (free catch method) and collecting the sample in a container as the bladder is compressed manually. After collection, the physical properties of the urine are evaluated. The volume, color, odor, transparency, and specific gravity of the sample are observed and recorded (B). Normal urine is light yellow to amber in color, depending on the amount of water it contains. The odor of normal urine varies between species. The urine of most animals is clear or transparent; however, equine urine normally contains mucus, which gives it a cloudy appearance. Specific gravity (SG) is a reflection of the concentration of the urine and is measured using an instrument called a refractometer. Normal specific gravity measurements vary among species. Chemical analysis of the urine sample is performed using a reagent strip (C). Each strip contains a series of pads, and each pad is impregnated with a chemical that causes a color change to indicate the presence of a particular substance in the urine. Urine is placed on the reagent strip using a pipette or syringe. The color change of the various reagent pads is observed at specific times and compared to a reference chart provided by the manufacturer. Chemical analysis reagent strips commonly provide information about urine pH and the presence of protein, glucose, ketones, bile pigments (bilirubin and urobilinogen), red blood cells, and white blood cells in the sample. Lastly, a microscopic examination of the solid components (sediment) of the urine sample is performed. To prepare the sample, urine is placed in a test tube and centrifuged to concentrate the sediment into a pellet at the bottom of the tube. The sediment is then examined microscopically for the presence of various microscopic elements such as red blood cells, white blood cells, epithelial cells, tubular casts, crystals (D), and microorganisms such as bacteria, fungi, and parasites. A thorough urinalysis is essential to identify conditions affecting the urinary system such as infections, crystalluria and urinary calculi, diabetes mellitus, and many others. Being proficient in performing a urinalysis is an important component of becoming an invaluable veterinary technician.

Renal Failure

Like any functional organ of the body, the kidneys can deteriorate and fail to work properly. Renal failure can be acute (sudden), and these cases are often caused by toxicity (exposure to toxins such as antifreeze or some pharmaceutical drugs) or decreased renal perfusion due to low a blood pressure event or systemic disease. Acute renal failure is caused by necrosis of the renal tubules resulting either from exposure to the toxic substance or from lack of blood flow. More commonly, however, renal failure is chronic, characterized by a progressive and irreversible destruction of nephrons over months to years causing a gradual loss of renal function. Chronic renal failure is a common disease condition of both cats and dogs. In the early stages of chronic renal failure, the glomerular fenestrations become larger than normal and allow larger molecules such as proteins to pass into the tubular filtrate. One of the earliest signs of chronic renal failure is proteinuria, or the presence of protein in the urine. Unfortunately, at this stage, there are no clinical signs that we can observe. This proteinuria can only be detected by urinalysis (see Clinical Application on urinalysis), which is often not performed in the absence of clinical signs. As the renal failure progresses, complete destruction of nephrons follows. The kidneys do an amazing job of compensating for this loss until enough nephrons are lost that those left can no longer filter the blood sufficiently and remove unwanted toxins. It is not until two thirds of the nephrons have been lost that clinical signs of renal failure start to appear! This is a double-edged sword. On the one hand, the kidneys are able to compensate and continue adequately to remove enough waste products from the blood, even working at decreased capacity. On the other hand, however, it is not until renal failure reaches the end stages, when little can be done to improve the quality or length of life, that we often diagnose its presence. When nephron destruction reaches this critical point, the kidneys lose their ability to perform their basic duties: filtration, reabsorption, and secretion. With glomerular damage, important blood proteins are lost into the urine because of impaired filtration. In addition, an increased amount of water is lost in the urine instead of being reabsorbed, causing dilute urine and dehydration of the patient. Also, waste materials that the kidneys normally eliminate through secretion accumulate in the body and cause many of the clinical signs of renal failure. Two of the main nitrogenous waste products that the kidneys normally eliminate are urea and creatinine, both by-products of protein metabolism. The accumulation of urea in the blood is called uremia, whereas the buildup of creatinine is called azotemia. Levels of these substances can be measured by performing blood chemistry analysis (see figure). The buildup of these toxins is mainly responsible for the nausea and vomiting that often characterize advanced renal failure. The goals of treating chronic renal failure are to slow the progression of the disease and improve the quality of life of the patient by treating the clinical signs. Fluid therapy is the mainstay of treatment for renal failure. Increasing the flow of fluid through the kidneys facilitates removal of urea and creatinine and improves hydration. If the animal is being kept in the hospital, fluids will likely be administered intravenously. If the patient is being treated by the owner at home, the owner can often be trained to administer fluids subcutaneously on a daily basis. Renal patients are often fed a diet that contains lowered levels of protein, as well as low levels of several minerals (such as phosphorus) that the kidneys are no longer able to remove sufficiently.

Cancer

The word cancer is frightening to many of us. It is mysterious in its ability to affect some animals and people and not others. Sharks, for example, rarely develop cancer, whereas certain breeds of dogs, such as Boxers, are considered "tumor factories" by many veterinarians. Why is it that some of us have had or will have cancer, but others of us will not? The causes of cancer are complex. Many factors influence the development of a normal cell and transform it into a killer. Environmental pollutants, certain food additives, radiation, some kinds of viruses, and certain chemicals have all been known to be carcinogenic (cancer causing). Also, certain genes have been linked to cancer in humans, and we see indications of this in animals as well. Rats, for example, carry a high risk of developing mammary carcinoma, and large dogs are far more likely to develop osteosarcoma, a tumor of bone, than small dogs. Cancer develops when cells lose their normal control over cell division. Any cell can become cancerous and can divide unchecked in any tissue anywhere in the body. When cells proliferate excessively, they form abnormal masses called neoplasms, which are classified as either benign (kind) or malignant (mal meaning bad). Benign neoplasms are well circumscribed and may be encapsulated. Because they do not spread to other parts of the body and tend to grow slowly, they are rarely of danger to the patient as long as they are not affecting vital organs. Some benign neoplasms, such as lipomas, are common in older animals and are often found in the subcutaneous fat layer. Malignant neoplasms, on the other hand, are invasive, aggressive, and can spread to other parts of the body and form secondary tumors. Malignant cells are less sticky than normal cells and therefore tend to break away from the primary tumor. These cells are carried through blood and lymph to other parts of the body, where they may establish secondary tumors. This process is called metastasis, and the secondary tumors are called metastatic masses. In animals, primary lung cancer is extremely rare because animals do not smoke, which is the leading cause of lung cancer in humans. Thus, when an animal is found to have lung cancer, every effort is made to find another tumor—the primary tumor—somewhere else in the body. Malignant cells form disorganized clumps, rather than the neatly arranged rows of cells seen in normal tissue. Because they have lost their sense of contact inhibition, malignant cells invade the surrounding normal tissue by "walking over" the normal cells. In contrast, benign cancer cells tend to push the normal cells away. The invasive nature and ability to metastasize make complete surgical removal of malignant cancer difficult. Cancer cells also tend to be immature in nature and tend to be larger and less differentiated than their normal adult counterparts. So how do the carcinogenic chemicals, viruses, and genes actually cause cancer? The answer is deceptively simple: they cause mutations in the DNA which alter the expression of certain genes. Genes that were permanently turned off may be 100turned on, and genes that should be turned on may be turned off. The cell is unable to perform normally because the programming has been altered. A proto-oncogene is a gene with fragile parts that are easily broken off or damaged by carcinogens. When the gene is damaged, it becomes known as an oncogene and provides incorrect instructions to the cell. Not all cancers are attributed to the formation of oncogenes, but their discovery has offered greater insight into the important relationship between carcinogens and genetics in the development of cancer.

Histopathology: An Introduction

Histopathology is the microscopic study of disease in tissues (histo- means tissue and pathology is the study of disease). The normal microanatomy of tissues is altered by pathologic disorders in many ways. For example, in mammary tissue that contains a malignant tumor, abnormally large, immature mammary cells may be evident microscopically. The nuclei of these cells are abnormally large, and many of the cells may be actively dividing. Other diseases, such as viral and bacterial infections, may cause cell death and create regions within the tissue that are dead or necrotic. Still other diseases may cause the abnormal accumulation of fluid, leading to a condition called edema, or may involve the accumulation of a waxlike glycoprotein called amyloid. Thus pathologic conditions may be evident microscopically as an increase or decrease in cell numbers, cell size, and changes in the cell's shape and in the architecture of the tissue's support structures. Although the pathologic nature of diseased tissue is often evident under microscopic examination, grossly the tissue may appear normal. For this reason, a definitive diagnosis often can be made only through the microscopic examination of tissue by taking a biopsy. Occasionally, aspirating cells from the tissue can lead to a diagnosis also. A biopsy is the removal of a small piece of tissue from an organ or mass. This may involve the insertion of a special kind of biopsy needle into the tissue, or it may involve cutting out, or excising, a piece of tissue with a scalpel. Some biopsy samples are obtained using special grasping attachments on the exploratory end of endoscopes; others may be acquired using a cookie-cutter type of instrument called a biopsy punch. Biopsy samples are harvested from the normal-abnormal tissue borders if possible. In addition, because the tissues are delicate, they should be cut with sharp instruments, such as scalpels, and maneuvered with tissue forceps, not dressing forceps, so that the microanatomy is not crushed. No matter how the sample is obtained, it must be handled with care and specially prepared before it can be examined. Samples should be sliced so that each piece is no thicker than 1 cm, and these should be placed in a fixative solution of 10% buffered formalin. The ratio of the volume of formalin solution to the volume of tissue should be approximately 10 : 1, so the specimen can absorb enough fixative to preserve it in its thickest regions. For example, if a large section of heart from a Doberman Pinscher is stuffed into a small container of formalin, the fixative may not be able to penetrate the tissue adequately and the heart will degenerate. Thus the architecture of the muscle will be lost, and a potential diagnosis of dilated cardiomyopathy, for example, will be impossible to confirm. Encapsulated or very fibrous tissues are also difficult to fix. A good rule of thumb is to make sure that the tissue is freely mobile in the container of formalin. Conversely, samples that are extremely small are sometimes invisible within a sea of formalin and are seemingly lost. In these cases, reports stating "no sample found" are returned to the clinician. Therefore, minute specimens should be placed in small, labeled cassettes.

Uroliths and Urolithiasis

Urine normally contains waste products dissolved in water. Some of these waste products are just barely soluble and, under certain conditions, they will precipitate out of solution to form crystals. This may not cause problems if the crystals move through the urinary system rapidly. If their transit time through the urinary system is prolonged, they may interact with each other and form aggregates known as uroliths, urinary stones, or urinary calculi. Uroliths are commonly seen in dogs, cattle, sheep, and goats (A) but are uncommon in horses. They take on a slightly different morphology in cats. (Refer to the Clinical Application on feline urolithiasis.) All uroliths have an organic matrix that stays fairly constant and makes up about 2% to 10% of its structure. The remaining 90% to 98% of the urolith structure is made up of one or more of about 20 different minerals. Some of the more common mineral compounds involved are magnesium ammonium phosphate hexahydrate (struvite), calcium oxalate, calcium phosphate, urate, ammonium urate, and cystine. Struvite stones are the most common stones found in dogs. Calcium carbonate, struvite, and calcium oxalate stones are some of the more common stones found in ruminants. The mechanism of urolith formation is not understood. We know that uroliths form when there are adequate amounts of the minerals present in the urine, the transit time of crystals through the urinary system is lengthened, and the pH of the urine favors precipitation. Some crystals stay in solution in acidic urine but precipitate out of solution in alkaline urine (e.g., struvite crystals), and other crystals stay in solution in alkaline urine but precipitate out of solution in acid urine (e.g., urate crystals). Diet, frequency of urination, urinary tract infection, and urine volume can influence these factors. For example, diet and the presence of certain bacteria associated with urinary tract infections can influence the pH of the urine. In addition, a housebroken animal that must consistently hold its urine for long periods of time will have a decreased crystal transit time through the lower urinary tract (bladder and urethra). Urolithiasis (the presence of urinary stones) can occur anywhere in the urinary system (the kidneys, ureters, urinary bladder, or urethra). Clinical signs associated with uroliths depend on where the stones are located. Some stones may cause no noticeable signs. Others may cause inflammation of the bladder (cystitis) or urethra (urethritis) or an obstruction anywhere along the urinary tract (B). Urethral obstruction is more common in males in general; in male ruminants, it occurs most often at the urethral sigmoid flexure (see Chapter 19). If the stone is obstructing the renal pelvis or ureter of one kidney, urine is prevented from leaving the kidney, and the pressure in the nephrons from fluid backup will eventually destroy that kidney. As long as the other kidney is functioning normally, no clinical signs may be evident. Remember that two thirds of the nephrons in both kidneys must be nonfunctional before clinical signs of renal dysfunction start to become evident. Treatment of urolithiasis is aimed at removing the stones and preventing them from forming again. There are commercially available diets for dogs and cats that dissolve and prevent some types of stones. Some stones will have to be surgically removed. In ruminants, surgical removal of the stones is often necessary. Diets and urinary tract infections have to be controlled to prevent urolith recurrence.

Glucocorticoid-Related Diseases

A condition that results from too much glucocorticoid hormone being produced by the adrenal cortex is hyperadrenocorticism, sometimes called Cushing's disease. Initial clinical signs include polyuria (excess urine production), polydipsia (excess water consumption), and polyphagia (increased appetite). Long-term signs include hair loss, muscle wasting, and slow wound healing. The signs of naturally occurring hyperadrenocorticism can be mimicked by administration of high doses of corticosteroid drugs. Hypoadrenocorticism (sometimes called Addison's disease) is a condition caused by a deficiency of adrenocortical hormones. Clinical signs are somewhat nonspecific, including weakness, lethargy, vomiting, and diarrhea. It is usually a progressive condition that can lead to circulatory problems and kidney failure. The effects of the disease can be mimicked if long-term corticosteroid drug administration is suddenly stopped.

Abdominal Incisions

Abdominal surgery is commonly performed on veterinary patients. From rumenotomies in cattle to ovariohysterectomies (spays) in dogs, abdominal surgical procedures have one thing in common—the surgeon must make an incision somewhere in the abdominal muscles to expose the contents of the abdomen. The location of the incision is usually carefully selected to offer maximum exposure of the required organ or structure. It will also allow a secure closure when the surgical procedure is over and the incision is sutured shut. The positions and arrangements of the abdominal muscles and the direction in which their fibers run are important considerations when choosing the site for an abdominal incision. The most common abdominal incision site is the ventral midline, where the linea alba is located. It offers several advantages over other sites, such as excellent exposure of abdominal organs, easy closure, and few sensory nerves. Nearly all abdominal organs and tissues can be reached through a ventral midline incision. Also, because all of the abdominal muscles come together at the linea alba, an incision through it opens the abdomen in one cut. When it is time to close the abdomen, one layer of sutures (stitches) in the linea alba can effectively and securely close the abdominal cavity. The linea alba contains fewer sensory nerves than the adjacent muscles, therefore less postoperative pain is involved with a ventral midline incision than with other abdominal incision sites. The only real disadvantage of a ventral midline incision is that the weight of all the abdominal contents presses on it during the healing process, so it must be closed with very secure sutures. At times, however, a ventral midline incision is not practical, such as when a cesarean section must be performed on a cow. The complicated digestive system of a ruminant animal like a cow can make it dangerous to position the animal on its back for a surgical procedure. Therefore abdominal surgery in cattle is often done with the animal standing and wide awake. Local anesthetic blocks are used to numb the flank (side) area. The incision is usually made in an up-and-down (dorsal-ventral) direction in the flank area. This means that three layers of muscle—the external abdominal oblique, internal abdominal oblique, and transversus abdominis muscles—must be cut to gain access to the abdominal cavity. To minimize trauma and allow normal function after surgery, many surgeons suture each muscle layer individually according to the direction that its fibers run. Optimal closure of this type of incision requires a separate layer of sutures for each muscle layer that was incised, which entails a lot more work than suturing closed a ventral midline incision. Several other common abdominal incisions can be used, such as the paramedian incision (parallel to, but beside, the ventral midline), the paracostal incision (parallel to, and just behind, the last rib), and the transverse incision (crosswise, perpendicular to the linea alba). The abdominal muscles present at each incision site determine how the abdominal cavity should be entered and how it can be sutured most securely. (See, this anatomy stuff is important even after you're done with your anatomy class!)

Roaring in Horses

An abnormal respiratory condition that is sometimes seen in horses is called roaring, which is the common name for laryngeal hemiplegia. Hemi means "half," and plegia means "paralysis"; therefore, laryngeal hemiplegia literally means "paralysis of half of the larynx." Actually, it is a paralysis of the muscles that tighten the arytenoid cartilage and vocal cord on one side (usually the left) of the larynx. The result is that the affected vocal cord just "flaps in the wind" as the animal breathes. It usually does not cause a problem when the animal is at rest, but when the animal exercises and breathes heavily, the paralyzed vocal cord partially obstructs the glottis each time the animal inhales. This produces the characteristic "roaring" sound as the animal breathes and makes it difficult for the animal to get enough air. The lack of air causes the animal to tire quickly, thereby producing what is known as exercise intolerance. The cause of roaring is a congenital (present at birth) degeneration of the left recurrent laryngeal nerve that supplies the muscles that tighten the left arytenoid cartilage. The cause of this degeneration is not known, but it may be an inheritable genetic defect. In other words, it may be a trait that can be passed on to offspring by affected parents. The treatment of roaring usually requires surgery to stabilize the "loose" side of the larynx. The most common procedure is laryngeal ventriculectomy (removal of the lateral ventricle on the affected side). The purpose of the procedure is to produce enough scar tissue as the area heals to tighten the affected cartilage and vocal cord and hold it out of the airstream. It does not cure the condition, but it may lessen the severity of the clinical signs. More extensive (and expensive) surgical procedures are sometimes performed on affected high-value animals, such as racehorses.

Atomic Force Microscopy

An atomic force microscope (AFM) generates a three-dimensional image of incredibly small structures using a minute sharp-tipped probe attached to a delicate cantilever (arm). The tiny probe meticulously scans the surface of specimens, allowing the forces between the tip and the sample surface to deflect the cantilever. This deflection is recorded by a computer, which generates a digital image. Some of the forces that can cause deflection include capillary forces, chemical bonding, electrostatic and magnetic forces, as well as mechanical contact forces. In most AFMs, a feedback mechanism is employed by the computer to adjust the tip-to-sample distance so that a constant force is maintained between the tip and the sample. In this way, the tip and sample are prevented from banging into one other causing damage to either the sample or the tip. The tip of the probe is often covered with an array of special coatings depending upon what forces are being investigated. For example, a gold coating is used to trace covalent bonding in organic molecules, diamond coatings are used to increase the wear resistance of the probe and magnetic coatings are used to evaluate magnetism on the surface of a specimen. The probe can scan the surface of specimens in a static (or contact mode), or via a dynamic (noncontact) mode in which the probe is vibrated. The results are magnificent three-dimensional images on a scale far smaller than previously thought possible. The use of AFM technology has enabled scientists to look more deeply inside cells and to visualize the minute anatomical structures that are necessary for life. Thus, AFM has led to a greater understanding of the cause of some diseases that have devastated both humans and animals.

Anabolic Steroid Drugs

Anabolic steroid drugs, which are related to testosterone, are used to help debilitated animals regain strength and weight after surgery or long illnesses. Unfortunately, they are sometimes abused by people seeking a shortcut to muscular development and performance enhancement. Because of their similarity to the hormone testosterone, they have many undesirable side effects that alter reproductive functions, behavior, and other body systems.

A Pint's a Pound the World Around

Another way to determine the total blood volume is to figure that blood makes up an average of 6% to 8% (average 7%) of an animal's lean body weight. Of course, that will give you the weight of total blood volume, so you need to convert that to a liquid measure. A pint of water weighs a pound. Therefore, because blood is mostly water, we'll use that conversion rate. From here we need to convert it into metric measurements because that's how syringes are calibrated. There are 2 pints in a quart, and a quart is approximately equivalent to a liter. There are 1000 ml in a liter. So now it becomes a simple math problem. Using these guidelines, a dog weighing 75 lb (34 kg) will have a total blood volume of approximately 5.25 lb (75 pounds × 7%). That's 5.25 pints of blood. If 2 pints are 1 quart, 5.25 pints are 2.625 quarts, or approximately 2.625 liters. Move the decimal point to the right three places and the total blood volume of this dog is 2625 ml. A 200 ml blood loss for this animal would amount to about a 10% loss of total blood volume. This would not be a significant loss for the dog. However, a cat weighing 10 lb (4.5 kg) will have a blood volume of 0.7 lb, or 0.7 pint. This converts to 350 ml. A blood loss of 200 ml would result in a loss of 57% of its total blood volume. The cat would probably die of shock before you could get that much blood out of it.

Diabetes Insipidus

Antidiuretic hormone (ADH) released by the posterior pituitary gland plays a major role in controlling urine volume by regulating water reabsorption from the collecting ducts. If the pituitary is not releasing adequate amounts of ADH, the collecting ducts will not reabsorb adequate amounts of water, and polyuria develops, along with a compensatory polydipsia. This condition is known as diabetes insipidus, and it has to be distinguished from diabetes mellitus. Both diseases are associated with polyuria and polydipsia, as are many other diseases. The urine produced in diabetes mellitus contains large amounts of glucose and therefore would taste sweet (if you were inclined to taste it to find out). The word insipid means tasteless. The disease diabetes insipidus was given its name because clinically it looked similar to diabetes mellitus; but the urine was tasteless, rather than sweet, because it didn't contain glucose. Another form of diabetes insipidus results from an inability of the collecting ducts to respond to the presence of adequate amounts of ADH. The clinical signs are the same. Further diagnostic testing would have to be done to reach a definitive diagnosis of diabetes insipidus. Like diabetes mellitus, diabetes insipidus occurs most often in dogs and cats among domestic species.

Cat Bite Wound

Any animal bite wound has the likelihood of becoming infected. Cat bite wounds, whether on humans or other animals, are especially contaminated and infection is almost guaranteed. The cat's mouth has a large number of normal flora. Upon penetration of the its teeth through the skin of a person or another animal, those bacteria are deposited deep into the wound where they are no longer normal flora. This deep location often has a low oxygen concentration and becomes an ideal breeding ground for bacteria. The body responds to the presence of these bacteria by sending phagocytic white blood cells to the site to phagocytize the bacteria. This large accumulation of WBCs is known as pus, which often leads to the formation of an abscess (an accumulation of pus in a confined space). Treatment of an abscess typically consists of lancing, draining, and flushing out the wound. Sometimes a drain is placed to allow for further pus to exit the wound. Cat bite wounds, or any penetrating wound, should be addressed quickly to avoid abscess formation. Hint: In the case of bite wounds, look for four puncture sites—one for each of the cat's canine teeth.

Electron Microscopy

As its name implies, electron microscopy uses electrons rather than light to create an image. An electron beam generated by an electron gun is directed with precision toward the specimen by magnets. Some of the electrons pass through the specimen, but some of them bounce off and are deflected to the sides. Electron beams are not visible to humans, and the generation of images in electron microscopes is therefore dependent upon an electron detector, which translates the pattern of incoming electrons into a readable image. The electron microscope is so powerful that it can make extraordinarily minute intracellular structures visible, including the organic molecules that compose cells. Interestingly, there is no color at this level of magnification, because the structures being examined are as small as, or smaller than, the wavelength of the colors we humans can see. However, computer enhanced coloration is used to augment the black and white world, creating images with greater clarity and definition. There are two types of electron microscope: transmission electron microscopes (TEM), which generate two-dimensional images; and scanning electron microscopes (SEM), which generate three-dimensional images. Transmission electron microscopy works by sending a beam of electrons through a specimen in the same way that light microscopy sends a beam of light through a specimen. Thus the specimen used in TEM, like light microscopy, must be very thin so that the electron beam can pass through it. Once the electrons pass through the specimen, they strike phosphorescent particles on a viewing screen, which release photons (visible light). In this way, the screen literally glows with the microscopic image. Specimens in scanning electron microscopy are first "sputtered" or covered with tiny particles of gold before they are examined. Inside the microscope, an electron beam is generated and is scanned back and forth over the specimen, hence the term scanning electron microscope. The electrons from the beam are deflected at the surface and secondary electrons are displaced from the surface as well. These primary and secondary electrons are detected by a sensor that relays the signal to an amplifier. The magnified image is subsequently displayed on a monitor.

Aspiration Pneumonia

Aspiration pneumonia is an inflammatory condition of the lungs produced by inhalation of foreign material. Common causes include oral liquids administered too rapidly for an animal to swallow and inhalation of regurgitated material by an anesthetized animal. It is a much easier condition to prevent than to treat. When large quantities of oral liquids are to be administered to an animal, care must be taken not to administer them faster than the animal can swallow. If the delivery rate is too rapid, the animal may inhale some of the fluid down into the lungs. The amount of damage caused depends on the quantity and composition of the inhaled material. If the quantity is large or the material is irritating, the damage to the lungs can be considerable—even fatal. An anesthetized animal must be protected from aspiration of foreign material, because its swallowing reflex disappears as it becomes anesthetized. Anesthetized animals are often positioned horizontally with their heads at the same level as their stomachs, so it is easy for small amounts of stomach contents to be regurgitated up the esophagus into the pharynx. Without the protective swallowing reflex, the regurgitated material can be inhaled easily down into the lungs. The stomach contents are very acidic because of secretions from the stomach wall, so you can imagine how irritating that material can be to the delicate structures of the lungs. The biggest risk of aspiration in anesthetized animals is in those that do not have an ET tube in place. A properly sized ET tube effectively blocks foreign material from entering the larynx and trachea because it fills the lumen of the airway. Placement of ET tubes in anesthetized animals is always desirable to ensure an open airway and to prevent aspiration pneumonia. However, danger periods still arise even in animals that are intubated. Just before the ET tube is inserted and just after it is removed, the animal is potentially vulnerable to aspiration of liquids from the mouth, throat, or stomach. We must monitor animals closely during these periods.

Asthma

Asthma is a disease that causes the bronchial tree to become overly sensitive to certain irritants. Exposure causes inflammation with resulting thickening of the lining of the air passageways, excess mucus production, and bronchoconstriction that can range from mild and annoying to severe and life threatening. Asthma is seen less commonly in domestic animals than in humans. It occurs most often as an allergic condition in cats that is usually chronic and progressive, and for which there is, as yet, no cure. Mild attacks can cause signs such as wheezing and coughing. More severely affected animals may show severe dyspnea (difficulty breathing), cyanosis (bluish color of the gums and lining of the eyelids), and frantic attempts to get air. Preventing asthma attacks usually involves trying to minimize the cat's exposure to potential allergens and irritants such as litter box dust, cigarette smoke, perfumes, pollen, air fresheners, molds, and hair sprays. Treatments range from emergency treatments with inhaled medications to long-term treatments with bronchodilators and anti-inflammatory drugs to help prevent attacks.

The Afterbirth

At birth, the placenta is often referred to as the afterbirth because it is delivered after the offspring. What actually happens is that the fetus is delivered through the placenta. The powerful contractions of uterine and abdominal muscles during labor cause the membranes of the placenta to rupture and release their fluid. This is called the water breaking. Often the amnion still partially covers the newborn after it is delivered. The dam will usually lick this off, starting at the face so that the newborn can draw those important first breaths. If the mother does not perform this important duty, humans must intervene if they are present. The membrane is very soft and is easily broken and pulled away from the newborn's face. Few things in veterinary medicine are more rewarding than removing the membrane from the face of a newborn animal and watching it take its first breaths!

Thermolabile Enzymes

Because enzymes are protein molecules with complicated three-dimensional structures, they are able to bend and move to accommodate bonding activities. Their shape is critical in enabling the enzyme to bond with the correct substrate. However, the shape of the binding site in some enzymes is affected by changes in the surrounding temperature. These enzymes are called thermolabile enzymes, because changes in temperature bring about changes in the structure and shape of the enzyme molecule. For example, in the Siamese cat, a thermolabile enzyme that affects coat color functions well at cooler temperatures but is rendered nonfunctional at higher temperatures; therefore, a dark brown or black pigment is produced in the cooler regions of the body, such as the tips of the ears and the tail, face, and paws, but not in warmer areas, such as the torso, neck, and thighs. Himalayan rabbits also carry thermolabile enzymes that affect coat color. For example, Himalayan rabbits raised at temperatures of around 5° C are entirely black; those raised at moderate temperatures are white with black ears, tail, and paws; and those raised at temperatures above 35° C are completely white.

Navicular Disease in the Horse

Because of its location deep in the hoof, where powerful forces are placed on it with each step, the navicular or distal sesamoid bone is subject to chronic wear and injury. This is particularly true in the front feet because of their more upright position. When the bone starts to undergo chronic, painful degeneration, the condition is called navicular disease. Navicular disease is not one specific disease with one specific cause; it is a complex syndrome that involves many factors, including damage to the bone itself, damage to the bone's blood supply, and damage to surrounding structures, such as bursas, tendons, and ligaments. The net result is a lameness that begins intermittently and progressively gets worse. The animal tries to shift weight off the heel area of the affected foot where the damaged navicular bone is located. This changes the animal's gait and can lead to secondary problems. The signs of navicular disease can sometimes be managed, but the condition is usually not curable. Some pain relief sometimes can be provided with corrective hoof trimming and shoeing and with drug therapy.

Growth Hormone (GH)

Because of its whole-body effects, deficiencies or excesses of GH can produce some very obvious effects. The most pronounced effect of a GH deficiency is dwarfism, a condition in which a young animal does not grow normally. Other, less dramatic effects of GH deficiency relate to its metabolic effects and interrelationships with other hormones and endocrine glands. These can include alopecia (hair loss), thin skin, and development of secondary abnormalities of thyroid, adrenal, and reproductive hormones. Animals with GH deficiencies often respond to the therapeutic administration of GH. An excess of GH can result in a form of gigantism referred to as acromegaly. The cause of this condition is often a pituitary gland tumor. A synthetic GH-like drug is also used to increase milk production in dairy cows. The drug bovine somatotropin (BST) is used for its generalized anabolic effect, which enhances the production of milk by the mammary glands. As is often the case with hormone-related drugs, some potentially serious side effects are associated with the use of BST. The drug is known to elevate animals' body temperatures, reduce conception rates, increase the risk of mammary gland infection (mastitis), and increase the risk of digestive disorders.

Blood Glucose and RBC Metabolism

Blood is living tissue even after it's been taken from an animal. A fresh blood sample in a tube still contains living red blood cells that utilize plasma glucose for energy. The problem is that there is no way for the glucose to be replenished in a tube after the red blood cells have used it. Clinical laboratory analysis of a blood sample frequently involves measuring blood glucose levels to look for or monitor diseases such as diabetes mellitus. A patient with uncontrolled diabetes will have an elevated blood glucose level. If red blood cells are not removed from the blood sample quickly enough, they could eat up enough glucose to bring an elevated blood glucose level down into the normal range. This could lead to a misdiagnosis and possibly inappropriate treatment. Red blood cells could even utilize enough glucose to take a normal blood glucose level down below normal. Samples that sit around long enough before the red blood cells are removed can have a blood glucose level of zero. Therefore, when the blood glucose level is to be measured, centrifuge the sample and remove the red blood cells soon after the sample is drawn to get an accurate result.

Thyroid Dysfunction

Because of the thyroid's many important roles, dysfunction of this gland can have serious effects on the health and well-being of an animal. Three conditions most commonly seen are goiter, hypothyroidism, and hyperthyroidism. Goiter manifests itself as a nonneoplastic (noncancerous), noninflammatory enlargement of the thyroid gland. It usually results from an iodine-deficient diet. Because iodine is an important component of thyroid hormone, a deficiency of iodine results in a deficiency of thyroid hormone. The anterior pituitary attempts to compensate for this by producing more thyroid-stimulating hormone (TSH). The elevated TSH levels overstimulate the thyroid and cause hyperplasia (overdevelopment) of the gland. This causes it to enlarge, resulting in what we call goiter. Although goiter can be treated with iodine supplementation, it is more easily prevented than treated. In areas known to be iodine deficient, iodized salt should be added to animals' diets. Hypothyroidism results from a deficiency of thyroid hormone. It is most commonly seen in dogs, although it can be seen in any species. Because thyroid hormone influences the functioning of all cells, organs, and systems, hypothyroidism affects the whole body. This results in clinical signs that are vague and nonspecific. They relate primarily to a slowing of the body's metabolism. Common clinical signs include alopecia, or hair loss (usually bilaterally symmetric), dry skin, lethargy, reluctance to exercise, and weight gain without any increase in appetite. Affected animals often seek out sources of heat, because deficient thyroid hormone levels cause the animal to have difficulty maintaining its body temperature. Most cases of hypothyroidism occur in middle-aged animals, but if it occurs in a young animal, dwarfism (impaired growth) and impaired mental development occur along with the other common signs. Hypothyroidism often can be treated effectively by administering thyroid hormone supplements to affected animals. These supplements are usually in the form of the prohormone T4, or thyroxine. The body then converts the T4 to the active hormone T3 as needed. Thyroid supplements usually have to be continued for the rest of the animal's life. Hyperthyroidism is the opposite problem. It results from too much thyroid hormone production. It is most commonly seen in cats, although it is seen occasionally in dogs. Excessive amounts of thyroid hormone speed up cellular metabolism all over the body. This results in signs such as nervousness, excitability, weight loss, increased appetite, tachycardia (abnormally fast heart rate), vomiting, diarrhea, polyuria (excessive urine production), and polydipsia (excessive thirst). Hyperthyroidism is usually treated either by surgical removal of the thyroid gland (thyroidectomy) or by long-term administration of a thyroid-inhibiting drug.

Hormones as Drugs

Because of their powerful and often widespread effects, hormones and hormonelike substances are used as drugs to treat illnesses or to produce particular desired effects in animals. When natural hormone levels are too low, hormones can be given therapeutically to help correct the imbalance. This is often the case with hypothyroidism (deficiency of thyroid hormone), diabetes insipidus (deficiency of antidiuretic hormone), and diabetes mellitus (deficiency of insulin). In other cases, drugs derived from natural hormones are used to produce particular effects, such as an anti-inflammatory effect (glucocorticoid-like drugs) or stimulation of uterine contractions (oxytocin), cardiovascular stimulation (epinephrine), or to synchronize estrous cycles (prostaglandin F2α). Because the production and effects of natural hormones are so interrelated, the therapeutic use of hormones and hormonelike drugs can produce some potent and widespread problems, along with beneficial effects. The amounts of hormones used therapeutically are usually very large compared with the normal physiologic hormone levels in the body, therefore the potential for undesired side effects increases accordingly. For example, use of a hormonelike drug can inhibit production of the natural hormone it mimics. Later, when the drug is to be discontinued, the animal should be gradually weaned off it so that the natural hormone production mechanisms can gradually take over again. Suddenly stopping the drug after long-term administration can produce disastrous results. In general, hormone therapy must be carefully planned and closely monitored so that the benefits outweigh the consequences.

Intramuscular Injection Sites

Because skeletal muscles have large blood supplies, drugs injected into them are absorbed into the bloodstream and quickly carried off to the rest of the body. This method of drug administration is called an intramuscular injection (IM injection), and it is commonly used, particularly when a rapid drug effect is desired. An intravenous injection (IV injection), into a vein, provides the fastest method of drug distribution. An IM injection is the next fastest. In theory we should be able to use any skeletal muscle for an intramuscular injection. In practice, however, only a few muscles are suitable in each species. Many muscles are either too small or too thin to allow such an injection; others have prominent structures nearby, such as nerves that could be damaged by the injection. To be useful for an intramuscular injection, a muscle must be fairly large, must be easily accessible, and must have a sufficiently thick "belly" into which we can deposit the drug.

Fun Facts About Human Intervertebral Discs

Because we walk upright, gravity compresses our intervertebral discs slightly when we are up and moving around during the day. At night when we lie down and sleep, the compression stops and the discs expand back to their original size. The compression and expansion of each individual disc are very slight but, when combined, the variation in the total length of the spine is measurable. As a result, we are tallest in the morning—by as much as an inch! We proceed to get shorter throughout the day. For astronauts living in the microgravity environment of space, the result is even more impressive: after just a few days in space, their spines can expand up to 2 inches or more. Some astronauts report back pain during the first few days in space because this spinal expansion stretches the muscles around the spinal column. This dramatic increase in height is temporary, and astronauts quickly return to their normal, terrestrial height when they return to earth.

Anticoagulants, Plasma, and Serum

Blood clotting factors found in plasma need to be present in sufficient quantities for blood to clot. If we want to prevent blood from clotting, we need to add something to it that ties up one of the clotting factors. Substances that tie up clotting factors and prevent blood from clotting are called anticoagulants. (Coagulation is another word for clotting.) If an anticoagulant is added to a blood sample in a tube or syringe, the blood will not clot. One of the most common anticoagulants is ethlyenediaminetetraacetic acid or EDTA. EDTA prevents clotting by tying up calcium, clotting factor number IV. If even one clotting factor is absent the blood will not clot. No calcium, no clot. If anticoagulant is added to a blood sample as it is drawn from an animal, the sample will not clot because all the clotting factors are not present. If the blood sample is then centrifuged (spun at a high speed), the fluid that rises to the top of the tube is plasma. If no anticoagulant is added to a blood sample as it is drawn from an animal, the blood will clot. If the clotted blood is centrifuged, the fluid that rises to the top of the tube is called serum. When blood clots, one of the dissolved plasma proteins—fibrinogen—is converted to insoluble fibrin, which precipitates out of solution as a meshwork of tiny fibers (hence its name) and helps make up the framework of the clot. Removing fibrinogen from plasma by allowing it to clot converts plasma to serum. Many of the diagnostic clinical chemistry tests performed on a patient sample are run on either plasma or serum. After the sample has been centrifuged, the plasma or serum can be drawn off and analyzed or frozen for analysis at a later date. Whole blood cannot be frozen, because blood cells rupture easily during the freezing and thawing processes.

Using External Skeletal Landmarks in Body Condition Scoring

Body condition scoring (BCS) uses a numerical scale to indicate the amount of fat in an animal's body. The details of different BCS systems vary, but most use either a 9-point or 5-point scoring system. In each case the middle of the range, 5 out of 9 (BCS = 5/9) or 3 out of 5 (BCS = 3/5), is the desired body condition status. An animal with a low BCS is too thin: a BCS of 1/5 or 1/9 means the animal is emaciated. An animal with a high BCS is overweight: one with a BCS of 5/5 or 9/9 is obese. Regardless of the BCS system being used, the basic technique involves visually assessing the animal's body shape, and palpating (feeling) external skeletal landmarks to determine how much fat is around them. Common skeletal landmarks used in body condition scoring include ribs, vertebrae (wings of atlas, spinous processes, transverse processes), shoulder (greater tubercle of humerus, spine of scapula), elbow (olecranon process of ulna, epicondyles of humerus), pelvis and hip (ilium, ischium, greater trochanter of femur), and stifle (patella, epicondyles of femur). The more prominent these skeletal landmarks are, the lower the amount of fat in the animal's body, and the lower the BCS. Conversely, the more difficult these landmarks are to feel, the greater the amount of fat in the body, and the higher the BCS. Author's note: Precise BCS criteria vary from species to species. (Enter "Body Condition Scoring" into your favorite internet search engine to see some examples.) But the basic concepts can be applied to virtually any animal species. At the zoo I am often asked by zookeepers to assess their animals' body conditions. They use those values along with body weights to judge whether the animals' diets are appropriate. On a given day I may evaluate the BCS of a chinchilla weighing less than a pound, and that of a camel weighing a ton. The same basic principles apply to each.

Fracture Repair

Bones are among the best healing tissues in the body. When bones are broken, three things are necessary for optimal healing to occur: alignment, immobilization, and time. The fractured ends must be brought close together in reasonable alignment and must be kept from moving apart until healing processes have had adequate time to effect new bone growth. Alignment of the fractured fragments is called setting or reducing the fracture; immobilization is called fixation of the fracture. External fixation devices such as splints and casts may be used, as can internal devices such as pins, wires, screws, or plates, which must be surgically implanted. The length of time that the fixation device must be kept in place varies with the type and location of the fracture and must take into consideration the physical characteristics of the animal. Factors such as species, age, physical condition, and size of the animal affect the speed of healing. In a small, young animal, the whole process might only take a couple of weeks; in an older or larger animal, it might take several months or more. Regardless of the type and location of the fracture, the basic healing processes are the same. The large blood supply of bones results in considerable bleeding (hemorrhage) at the fracture site. After the blood begins to clot, forming what is called the fracture hematoma, the bone is gradually infiltrated by healing cells and tissues over the next few weeks and months. Osteoblasts from the area form the healing tissue, called the callus, that gradually bridges the fracture gap. The callus can be felt as a lump at the fracture site, and the size of the callus is an indicator of how much movement has been occurring between the fracture fragments. The less movement, the smaller the callus. Fractures with small calluses generally heal faster, which is usually our treatment goal. Once the callus is fully formed and mineralized, the basic healing of the fracture is complete; however, what occurs after that is very important. Over the next few months, the body slowly remodels the bone at the fracture site according to the mechanical stresses that are placed on it. Ideally, this gradual remodeling will return the bone to its original size, shape, and strength.

The Role of Bones in Calcium Homeostasis

Calcium homeostasis is regulated by two calciotropic hormones, each of which has effects on bones. (Calcitropic means they are involved in the regulation of calcium levels in the body.) When the level of calcium in the blood begins to rise too high, the hormone calcitonin is secreted by the thyroid glands. This encourages calcium to be deposited in the bones by osteoblasts, inhibits bone reabsorption by osteoclasts, and increases the amount of calcium excreted by the kidneys into the urine. All of these actions help decrease the amount of calcium in the blood. When the level of calcium in the blood drops too low, parathyroid hormone is released from the parathyroid glands. This hormone inhibits calcium deposition in bones by osteoblasts, encourages osteoclasts to withdraw calcium from bones, and causes calcium to be retained by the kidneys by decreasing the amount excreted in the urine. These actions all serve to increase the amount of calcium in the blood. This depositing and withdrawal of calcium from the bones goes on constantly as the body's needs and the contents of its food supply change.

Canine Hip Dysplasia

Canine hip dysplasia is an abnormal looseness or laxity of the hip joints of some dogs that leads to joint instability and degenerative bony changes. Many factors contribute to its development, including overnutrition that leads to too rapid growth, exercise, and genetic factors. Puppies of dysplastic parents are more likely to develop hip dysplasia than are puppies of normal parents, and larger breeds are affected more often than smaller breeds. In a dysplastic animal, the normally tight-fitting hip joint is much looser, allowing the femoral head to "rattle around" in the acetabulum. This damages the joint surfaces and leads to degenerative changes and osteoarthritis. Movement of the diseased hips is painful, especially after exercise. Definitive diagnosis of canine hip dysplasia usually requires pelvic radiographs, and treatment can range from weight reduction and exercise restriction, to medical treatments with anti-inflammatory drugs, to a variety of surgical procedures. The best treatment for canine hip dysplasia is to attempt to prevent its development by only breeding hip dysplasia-free parents. Tibia

Vaginal Cytology in the Dog

Changes in the epithelial lining of the vagina during proestrus and estrus can be utilized to determine the most effective time to breed a bitch, or the most likely time she must be kept away from males to prevent unplanned breeding. The basic principle is that the vaginal lining becomes progressively thicker and the surface epithelial cells become increasingly cornified (keratinized) during the proestrus period, and this reaches a peak when the animal is in estrus and most likely to conceive if bred. The most common technique is to insert a saline-moistened cotton swab into the vagina while avoiding contact with the lining of the vulva. The swab is gently twirled or moved back and forth, removed, and rolled onto a glass microscope slide in several rows. Then any of several different stains are applied to make the epithelial cells more visible under the microscope.

Coughs, Sneezes, Yawns, Sighs, and Hiccups

Coughs, sneezes, yawns, sighs, and hiccups are temporary interruptions in the normal breathing pattern. They can be responses to irritation (coughs and sneezes) or attempts to correct imbalances (yawns and sighs), or they may occur for unknown reasons (hiccups). A cough is a protective reflex that is stimulated by irritation or foreign matter in the trachea or bronchi. It consists of a sudden, forceful expiration of air. Moist coughs, also known as productive coughs, help an animal clear mucus and other matter from the lower respiratory passages. They are generally beneficial to the animal, and we usually do not try to eliminate them with medications. Dry coughs, also known as nonproductive coughs, are generally not beneficial and are often treated with cough-suppressant (antitussive) medications. A sneeze is similar to a cough, but the irritation originates in the nasal passages. The burst of air is directed through the nose and mouth in an effort to eliminate the irritant. A yawn is a slow, deep breath taken through a wide-open mouth. It may be stimulated by a slight decrease in the oxygen level of the blood, or it may just be due to boredom, drowsiness, or fatigue. Yawns can even occur in humans by the power of suggestion, such as seeing someone else yawn or even thinking about yawning. (Did you just yawn?) A sigh is a slightly deeper than normal breath. It is not accompanied by a wide-open mouth, like a yawn. A sigh may be a mild corrective action when the blood level of oxygen gets a little low or the carbon dioxide level gets a little high. It may also serve to expand the lungs more than the normal breathing pattern does. Anesthetized animals are often manually given deep sigh breaths periodically to keep their lungs well-expanded. This is done to prevent the partial collapse of the lungs, which can occur in anesthetized animals as a result of respiratory system depression produced by general anesthetic drugs. Hiccups are spasmodic contractions of the diaphragm accompanied by sudden closure of the glottis, causing the characteristic "hiccup" sound. Although hiccups can result from serious conditions, such as nerve irritation, indigestion, and central nervous system damage, most of the time they are harmless and temporary. Many folk remedies have been suggested for hiccups, but because they are usually self-limiting, the best approach is to just let them run their course. However, prolonged or recurrent hiccups may require medical attention.

Dialysis

Dialysis is a type of diffusion used most commonly in animals with acute kidney failure, though animals with chronic renal failure may also be dialyzed as well (A). Common causes of acute renal failure may include infections, such as leptospirosis in dogs, pyelonephritis in cats, or toxins from the consumption of nonsteroidal anti-inflammatory drugs and ethylene glycol. Hypovolemic shock, which causes profound hypotension, may also cause an acute renal crisis. Hemodialysis can be performed in some veterinary hospitals to remove toxic substances that accumulate with renal failure, such as urea, uric acid, and creatinine. At abnormally high levels, these uremic toxins make animals feel nauseated, so they stop eating, lose weight, and become lethargic. Clinically, nausea in dogs often causes them to lick their lips excessively and often causes cats to drool. To remove these toxic substances, the animal's blood is circulated through a machine that includes a filtering apparatus called a dialyzer or artificial kidney (B and C). The dialyzer consists of a plastic cylinder filled with hundreds if not thousands of hollow, semipermeable filaments. Small molecules such as creatinine pass through the semipermeable membranes, but larger molecules, such as the protein albumin, cannot. Blood from the animal is pumped into the dialyzer (from the top, in this case) and flows within the thin fibers. A special electrolyte solution called dialysate is driven through the dialyzer filter in the opposite direction to the blood (from the bottom). This enables small solutes such as creatinine and blood urea nitrogen (BUN) to move out of the blood in the filaments and into the dialysate solution (i.e., to move from a higher concentration to a lower one). Dialysis is an excellent example of the use of basic scientific principles to help resolve a clinical problem. This deductive ingenuity has saved countless animal and human lives.

Disseminated Intravascular Coagulation (DIC)

Disseminated intravascular coagulation (DIC) is a condition that occurs as a complication of a variety of disorders, including hyperthermia. DIC is characterized by increased intravascular coagulation, worsened by the subsequent formation of microthromboses (clots) that lead to multiorgan failure. The result of DIC is either excessive bleeding or clotting which, without treatment, often leads to death. Animals with DIC typically show signs of bleeding, such as petechiae, ecchymoses, melena, and hematuria. Treatment involves remedying the initial cause of DIC by administering heparin, as well as blood product transfusion to replace consumed coagulation factors. Overall, the treatment or resolution of DIC is many times unsuccessful. DIC has also been called "Death Is Coming." The best way to prevent DIC is to treat the underlying cause rapidly before the sequence of DIC is initiated.

Superovulation

Drugs like FSH are often used to "superovulate" animals in preparation for embryo transfer. They cause the ovaries to produce more follicles and ova than normal. This production of larger than normal numbers of ova is called superovulation. Once the animal is bred, the resulting fertilized embryos are retrieved from the uterus (usually by flushing) before they implant in its wall. They can then be transferred to other recipient animals, whose estrous cycles have been synchronized with the donor animal, for the remainder of the gestation (pregnancy) period. This allows females of particularly good genetic stock to produce more offspring in their lifetimes than normal reproductive mechanisms would allow.

Glucocorticoid-Related Drugs

Drugs modeled after glucocorticoid hormones are commonly used therapeutically in animals, usually for their anti-inflammatory effect. This general class of drugs is commonly known as corticosteroids or glucocorticosteroids and includes drugs such as hydrocortisone, prednisone, dexamethasone, and triamcinolone. Because they mimic many of the effects of natural glucocorticoid hormones and are given in amounts much larger than the natural hormones, these powerful drugs have many potential side effects. These include the following: • Suppression of the immune response. This can lower an animal's defenses and make it more susceptible to infection. • White blood cell count alteration. As a result of corticosteroid drug administration, neutrophil numbers go up, and lymphocyte, eosinophil, and monocyte numbers go down. This mimics the body's natural stress response. If we're going to administer corticosteroid drugs to an animal around the time that blood is to be drawn for a complete blood count (CBC), the blood should be drawn before the drug is given. This approach avoids confusion in interpreting the results. • Slowing of wound healing. Scar tissue-producing fibroblast cells are inhibited. • Catabolic effect. After long-term corticosteroid drug use, the catabolism (breakdown) of protein can result in thinning of the skin, loss of hair, and a general loss of muscle mass. • Premature parturition. Administration of corticosteroid drugs to pregnant animals can cause abortion of fetuses. • Hyperglycemia. This condition can be significant in an animal with diabetes mellitus, because it can change the animal's insulin requirement. • Suppression of adrenal cortex stimulation. The body's normal feedback mechanisms interpret the high levels of corticosteroid drug in the bloodstream as high levels of glucocorticoid hormones. This causes a cascade effect from the hypothalamus to the anterior pituitary gland to the adrenal cortex. The hypothalamus decreases its production of ACTH-releasing factor, which causes the anterior pituitary gland to decrease its production of ACTH. This results in diminished stimulation of the adrenal cortex. Long-term, high-level corticosteroid drug use actually can cause physical shrinkage (atrophy) of the adrenal cortex. If corticosteroid drug administration were then suddenly withdrawn, the animal would be left with a severe deficiency of glucocorticoid hormones. This would result in signs of hypoadrenocorticism (see the Clinical Application on glucocorticoid-related disorders). Therefore long-term use of corticosteroid drugs should not be terminated suddenly but tapered off gradually to give the adrenal cortex a chance to recover. • Iatrogenic hyperadrenocorticism. This can result when excessive levels of corticosteroid drugs are administered; iatrogenic means caused by treatment. Signs mimic naturally occurring hyperadrenocorticism.

Patent Ductus Arteriosus

During gestation, the fetal circulation does not carry much blood through the lungs; instead, there is an opening between the left pulmonary artery and the aorta that allows much of the blood that leaves the right ventricle to bypass the lungs on the way to the aorta and systemic circulation. Because the fetus does not breathe air—oxygen is provided to the fetus from the blood of the dam—there is only enough pulmonary circulation to nourish the tissues of the growing lungs. Following the rupture of the umbilical cord at birth, the fetus must generate its own oxygenated blood, so circulation through the lungs must be increased to include all of the blood that leaves the right ventricle. Normally, the shortcut opening between the pulmonary artery and aorta, known as the ductus arteriosus, closes soon after birth. Occasionally, the opening fails to close in the newborn, a condition called patent ductus arteriosus (PDA). Young animals with PDA suffer from inadequate oxygenation of their blood; in the long term, the condition is incompatible with life. PDA may be treated with drug therapy to promote closure, or surgical closure of the ductus arteriosus may be an option.

Liver and Kidney Failure

During protein catabolism, ammonia is produced. Because ammonia is toxic, it is converted by the liver to a nontoxic molecule called urea. Urea is a type of nitrogenous waste; it is a compound that contains nitrogen and is excreted. Nitrogenous waste is normally pulled out of the bloodstream by the kidneys and put into urine. When the kidney becomes diseased, however, it is sometimes unable to excrete urea effectively. The urea therefore builds up in the bloodstream, causing a condition called uremia. Uremia can be detected by a blood test that evaluates the blood urea nitrogen (BUN) level of the patient. Veterinarians look for this in the blood chemistry profiles of sick animals. Similarly, if the BUN is abnormally low, the veterinarian might suspect liver disease, because the liver is responsible for converting ammonia to urea. If the liver is not functioning normally, it cannot carry out this conversion. Can you guess what might happen to the ammonia level in an animal with liver disease?

Emesis

Emesis is a protective mechanism that provides animals with the ability to remove harmful or toxic substances from the stomach or upper intestine. Some species, such as swine, dogs, and cats, vomit easily. The vomiting reflex is controlled by the vomiting center in the medulla. The reflex begins with the animal taking a deep inspiration, followed by closure of the glottis and contraction of the abdominal muscles, but not the gastric muscles. The combination of abdominal muscle contraction and inspiration results in an increase pressure in the abdomen. This force is transferred to the contents of the stomach. The cardiac sphincter relaxes and food is forced into the esophagus. Antiperistalsis moves the food up the esophagus and into the oral cavity. Antiperistalsis is reverse peristalsis where the peristalsic wave moves partially digested food toward the oral cavity, as opposed to peristalsis that moves chyme toward the anus. Horses rarely vomit because their cardiac sphincter is so strong and because the angle at which the esophagus enters the stomach causes the stomach wall to push against the sphincter. The cardiac sphincter closes tightly when the stomach is full, making it difficult for it to open from a reverse direction. In the horse, attempting to vomit can increase the pressure in the stomach considerably, resulting in dilation and rupture of the stomach.

Endotracheal Intubation

Endotracheal intubation is a common clinical procedure in which a soft rubber or plastic tube, called an endotracheal (ET) tube, is inserted through the glottis and advanced down into the trachea. Its purpose is to provide an open airway, usually for the administration of an inhalant anesthetic, or to allow effective artificial ventilation. Techniques for passing ET tubes vary among species. In horses and cattle, species with long heads and soft palates, endotracheal intubation is often done blindly. The unconscious animal's head and neck are extended to give a straighter path into the larynx, and the ET tube is lubricated and gently inserted into the animal's mouth. It is then slowly advanced until it passes through the glottis and into the trachea. The long, soft palate forces the tip of the tube ventrally, so it usually enters the glottis on the first try. The soft palates of dogs and cats are generally too short for the blind technique to work. They are usually intubated with the help of an instrument called a laryngoscope. A laryngoscope consists of a battery-containing handle to which is attached a long, narrow blade with a small light source near the end. With the animal's head and neck extended, the laryngoscope blade is introduced into the mouth and advanced caudally until the epiglottis is identified. The tip of the laryngoscope blade is used gently to press the tip of the epiglottis ventrally. Once the epiglottis is out of the way, the arytenoid cartilages can be seen forming the entrance into the glottis. The tip of the lubricated ET tube is directed between the cartilages and down into the trachea. If the ET tube has an inflatable cuff (to provide a leakproof seal), the cuff is positioned just beyond the larynx to avoid passing the tube too far down into the trachea. If an ET tube is inserted too far, its tip can enter one of the two main bronchi. This can cause the other lung to collapse because it does not receive any air. In dogs, endotracheal intubation is usually just that simple. They generally have a large larynx that is easy to pass an ET tube into. A cat, however, usually has a more sensitive larynx. As soon as an ET tube touches any part of the glottis, it typically slams shut—a condition called laryngospasm. The purpose of this reflex is to prevent anything but air from entering the larynx. The way to get the tube through the sensitive opening is either to time the insertion of the tube for when the opening is of maximum size, during expiration, or to apply a small amount of local anesthetic to the glottis. This numbs the surface and temporarily eliminates the protective laryngospasm reflex.

Estimating Dehydration

Estimating Fluid Deficit from Dehydration: An estimate of the amount of fluid lost from dehydration (in liters) can be calculated by multiplying the percentage of dehydration by the weight of the animal in kilograms. Estimating Ongoing Fluid Losses: Sick animals lose fluid at a faster rate than healthy animals because of vomiting, blood loss, diarrhea, and elevated body temperature. Ongoing fluid losses can be quantified in hospitalized patients by collecting lost fluid. Urine, for example, can be collected in bags via urethral catheters and measured. Other body fluids can be collected from drains or in absorbable pads and subsequently weighed. The weight of the pad is subtracted to obtain the weight of the fluid alone. Assuming that a milliliter of lost fluid weighs one gram, an estimate of fluid loss can be calculated. For outpatients, getting a thorough history and knowing the frequency of incidents of vomition, urination, and diarrhea, as well as the volume of each incident, is helpful in estimating ongoing losses. However, this approach often underestimates the true fluid loss, so it is recommended that estimates be doubled to obtain a more accurate value. In general, replacement fluids should be administered over the same period of time as that in which they were lost. Fluids lost slowly, for example, should be replaced slowly and vice versa. Estimating Maintenance Fluid Needs: Maintenance fluids are administered to replace the fluids lost from normal physiologic activities such as sweating, breathing, urination, and defecation. The hourly maintenance rate in ml/hour is calculated using the formulae 132 × body weight (kg)(0.75) for dogs and 80 × body weight (kg)(0.75) for cats. In horses, 40 to 60 ml/kg/day is used to calculate the daily maintenance rate in adult horses, and 90 ml/kg/day is used for young foals.

Poisons That Affect the Nervous System

Every year, animals are injured or killed by nervous system poisons in the form of insecticides (flea products, bug sprays, agricultural chemicals), rodenticides (mice and rat killers), poisonous plants, or other chemical poisons that disrupt the function of the nerve synapse. Many of these poisons act by combining with or blocking the neurotransmitter receptors on the postsynaptic membranes. To combine with the receptors, these poisons must have a similar molecular structure to the natural neurotransmitters in the body. Many of these poisons bind to the receptors just like the natural neurotransmitters do, thereby stimulating the postsynaptic cell or neuron. In these cases of poisoning, we see an overstimulation of some aspect of the nervous system or the tissues innervated by that part of the nervous system. Animals may show signs of seizures or muscle tremors, indicating stimulation of the somatic motor system or overstimulation of the autonomic nervous system, resulting in vomiting or changes in respiration, heart rate, or other autonomic functions. In some cases, the poison can combine with the receptor, but it does not produce an effect. In this case, the poison would prevent the natural neurotransmitter from combining with the receptor to produce its normal effect. Because the poison acts as a blocker of that receptor, we would see a suppression of that part of the nervous system. A classic example of this effect is curare, the nerve poison found on the skin of the brightly colored poison dart frogs in South America. Curare combines with the receptors on skeletal muscles and prevents the presynaptic neuron's neurotransmitter from stimulating the muscle to contract; thus, curare paralyzes the animal's muscles. South American natives use this toxin to coat the tips of their hunting darts, arrows or spears to paralyze their quarry. In this way, the animals are easily captured, even if the wound itself is not fatal. We use a similar effect medically to paralyze the normal respiratory movements of animals during open chest surgery. By paralyzing the respiratory muscles, we can more easily mechanically ventilate, or breathe for, an animal without fighting its body's own contraction of the diaphragm and rib cage muscles.

Jaundice/Icterus

Excess red blood cell breakdown results in an excess amount of unconjugated bilirubin in plasma (hyperbilirubinemia). If the amount of unconjugated bilirubin exceeds the ability of the liver to conjugate it, the excess unconjugated bilirubin will be deposited in tissues. This causes the tissues to turn yellow, a condition called jaundice or icterus. These two terms are used interchangeably. Clinically, jaundice is most readily seen as a yellowish color of the mucous membranes and the whites (sclera) of the eyes. Jaundice can also be associated with liver diseases that prevent the liver from conjugating even the normal amount of unconjugated bilirubin presented to it. This causes the unconjugated bilirubin from normal red blood cell breakdown to build up in the blood and eventually be deposited in tissues. In other liver diseases, if the bile ducts are obstructed so the conjugated bilirubin can't be passed with bile into the intestines, conjugated bilirubin will eventually back up into the bloodstream and then into tissues. Jaundice again will result.

Tooth Resorption

Feline odontoclastic resorptive lesions were first discovered in the necks of teeth, which explains why these lesions were initially known as "neck lesions." Other species can also acquire similar lesions, so the name has been changed from feline odontoclastic resorptive lesion to tooth resorption. In this condition, tooth resorption occurs to form erosions, which are then covered with calculus or gingival tissue. Some affected animals will show signs of pain and discomfort, resulting in changes in behavior or appetite, whereas others show few symptoms. The level of treatment ranges from monitoring with minimal treatment to multiple tooth extractions.

Parvovirus: Killer of Intestinal Epithelia

Feline panleukopenia and canine parvoviral enteritis are life-threatening diseases that affect cats and dogs respectively. Parvoviruses, which cause both diseases, are highly contagious and are carried on clothing, shoes, and toys. They are shed in the feces and other excretions of affected animals and can be easily tracked into your house or veterinary office on the soles of your shoes. Fortunately, most cats and dogs are immunized against parvovirus and therefore never contract the disease. However, because of the highly contagious nature of these viruses, veterinary practices should isolate suspected carriers. For animals that do contract parvovirus, mortality is high if untreated, particularly in young animals. The virus attacks and kills cells that are actively engaged in mitosis. Thus tissues that are continually renewing themselves, such as epithelial tissue, may be devastated by parvovirus. The small intestine, for example, is lined with epithelial tissue that helps to absorb nutrient molecules from the lumen of the gut. During parvovirus infections, the epithelial cells die and slough in sheets and animals develop diarrhea, vomit, and can become severely dehydrated in a short time. The sudden loss of epithelial tissue causes bleeding into the intestine, which creates a distinctively noxious, foul-smelling, hemorrhagic diarrhea. A simple laboratory test on the stool may indicate the presence of the virus and offer a definitive diagnosis. Treatment centers on combating dehydration and includes intravenous fluid therapy with electrolyte supplements, antibiotics, and anti-vomiting medications. Animals that remain alive after 3 to 4 days of illness generally survive but continue to shed the virus for several months. Because of the highly contagious nature of parvoviral diseases, some veterinary personnel who own young animals change their clothes and shoes before entering their homes.

Feline Urolithiasis

Feline uroliths differ from uroliths in other species in that they are much smaller and resemble sand rather than large stones (see figure). Feline urolithiasis can be very irritating—like having sandpaper in the urine. If the sand contains a lot of the organic matrix, it clumps together to become a gelatinous plug with a gritty, toothpaste consistency. This plug can cause an obstruction, most often at or near the urethral orifice and most often in male cats. These are the "plugged tomcats" that are seen so often in emergency situations. Struvite and calcium oxalate uroliths are the most common types of urolith in cats. As with uroliths in other species, urine pH, diet, and the presence of a urinary tract infection play important roles in urolith formation. Keeping the urine acidic, sometimes with a special diet or medications, will keep the struvite in solution. Struvite crystals are composed of magnesium, ammonium, and phosphate, so a diet low in these substances may play some part in reducing the chance of crystals forming. If a plug has formed, it will have to be manually removed to prevent urinary bladder rupture or postrenal uremia from developing. One method of removal involves passing a catheter into the urethra and flushing the plug back into the urinary bladder. Manipulating the urine pH to make it more acidic can dissolve the plug. If back-flushing doesn't work, the plug may have to be surgically removed.

The Importance of Fluid Therapy

Fluid therapy is used to maintain hydration, to treat dehydration and to address ongoing fluid losses. It is also commonly used to maintain venous access during surgical procedures and in patients receiving intravenous medications. During emergencies, fluid therapy is used to increase oncotic pressure during hypovolemia and shock. It is used to improve urine production and output, and also to correct acid-base and electrolyte imbalances. Types of Fluid There are two general types of fluid administered: cystalloids and colloids. • Crystalloid fluids are composed of water that is rich in many different types of electrolytes. The solution can be either hypotonic (such as 5% dextrose in water, 0.45% sodium chloride, Normasol M, and Plasmalyte 56), or isotonic (such as Plasmalyte 148, Normasol R, and lactated Ringers solution). Because the solutes in crystalloids are small, allowing them to cross the vascular wall, crystalloids are particularly good for rehydrating extravascular spaces. They are also useful in correcting acid-base imbalances. • Colloid fluids are solutions containing large, heavy molecules suspended in an isotonic crystalloid. Because the large solutes are too big to cross the vascular wall, they 77remain in blood vessels and improve blood pressure by "holding" fluid in the intravascular space. Colloids may contain natural proteins such as albumin or synthetic molecules such as hetastarch. Therefore, they work well in patients with low plasma protein levels and in patients that are in cardiovascular shock. Administration of Fluids Fluid therapy is administered in three phases: 1. Resuscitation - The goal of fluid therapy during resuscitation is to increase the volume of fluid in the intravascular space and to raise blood pressure quickly. Patients in hypovolemic shock have lost about 30% of their blood volume. Shock doses for the colloid hetastarch are 20 to 30 ml/kg in dogs and 10 to 15 ml/kg in cats. The shock doses of an isotonic crystalloid are 80 to 90 ml/kg for dogs and horses and 40 to 60 ml/kg for cats. Using a mixture of both a colloid and a crystalloid during resuscitation has the benefit of an expansion effect with reduced side effects and a reduction in the total fluid dose. 2. Replacement - Replacement fluid therapy is administered to correct dehydration, replace fluid losses, and to provide for maintenance fluid requirements. Isotonic crystalloids are typically used during the replacement phase. 3. Maintenance - Isotonic crystalloids are typically used at a maintenance fluid rate in patients that are not drinking but have no level of dehydration and no ongoing fluid losses.

Hypersegmented Neutrophils

If a neutrophil nucleus in peripheral blood has more than five segments, it is called a hypersegmented nucleus. This indicates that the neutrophil has stayed in peripheral blood longer than normal, because hypersegmentation usually takes place in tissue as part of the normal aging process. The presence of hypersegmented neutrophils on a stained blood smear can be indicative of a pathologic condition that has prevented neutrophils from leaving the circulation, or it can mean the smear was made from old blood. Remember, blood is still living when it is removed from the animal, and it will continue the aging process as long as it can. Therefore, hypersegmented neutrophils may be just aging normally in the tube. Hypersegmented neutrophils are seen within a day after the blood sample was drawn. For this reason, it is important that a smear be made as soon as possible after the blood sample is drawn.

Genetic Disease: Be Careful What You Breed For

Genetic disease is caused by inheritable mutations of DNA. Any change to DNA, such as insertion, deletion, or mixing of the nitrogenous base pairs, leads to a nonsense sequence in the DNA. This defect can manifest as a disease in an organ system. Genetic diseases exist that affect the eyes, skeleton, skin, kidney, immune system, and enzymatic pathways. The defect may result in an incidental finding, such as microcytosis in Akitas, or the defect may cause life-threatening organ failure, such as copper-storage disease in Bedlington Terriers. Owing to the frequency of inbreeding in small animals, the most common type of disease that is seen is caused by inheritance of recessive traits. To inherit a recessive trait the animal must receive an affected chromosome from both parents. Obviously, affected animals are not bred, but a carrier animal may be inadvertently used in the breeding program. A carrier animal appears unaffected because it has an unaffected chromosome that is dominant over the recessive, affected chromosome. If two carrier animals are bred, each of the offspring has a 25% chance of being affected, inheriting the affected chromosome from each parent. They have a 50% chance of being a carrier by inheriting an affected chromosome from only one parent. When choosing which animals to breed, the ethical breeder will not breed relatives of any affected animals. If a relative of an affected animal must be used for breeding, there are tests available for some genetic diseases that will confirm whether or not the animal is a carrier. Some tests measure the production of abnormal proteins generated because of the DNA mutation. Carriers usually produce a small amount of the abnormal proteins. DNA tests can also detect the mutant genes for some diseases directly.

Glaucoma

Glaucoma is not one simple disease. Rather, it is a group of diseases characterized by increased intraocular pressure (pressure within the eye) that causes pain and can lead to blindness. In domestic animals, glaucoma is most often diagnosed in dogs, partly because it is seen fairly often in that species but partly because other species are not commonly tested for it. An instrument called a tonometer is used to test for glaucoma by measuring the intraocular pressure. Glaucoma can have many origins, but the basic mechanism is that aqueous humor is being produced at a faster rate than it is being drained from the eye. This causes the intraocular pressure to rise. Most often the problem is due to insufficient drainage of aqueous humor, rather than overproduction. Therapy for glaucoma usually involves medical or surgical treatments designed to increase the rate at which aqueous humor drains from the anterior chamber. The treatment of glaucoma usually is not as successful in domestic animals as it is in humans, because glaucoma is often in a very advanced stage when veterinary patients are presented for treatment. Unfortunately, glaucoma comes on very slowly and gradually with few, if any, clinical signs noticed early in the process, when treatment would be most beneficial. By the late stages, when the eyeball becomes noticeably enlarged and painful, it is often too late to save the animal's vision. In many cases, the affected eye must be surgically removed.

Dachshund With Intervertebral Disc Disease

Gretchen was an 8-year-old, spayed, female Miniature Dachshund brought in when it became apparent that she was suddenly unable to move her hind legs. On examination, the veterinarian observed that Gretchen could not stand on her rear legs and did not yelp when the skin on her rear toes was pinched. She did, however, react to firm squeezing of the toes themselves. The veterinarian concluded that spinal cord trauma was interfering with the sensory impulses reaching the brain and with conscious motor impulses from the brain reaching the muscles of the hind limb. Given the history and Gretchen's breed, spinal trauma from the rupture of an intervertebral disc seemed the most likely cause. In these situations, the material from the disc between vertebrae can rupture forcibly against the adjacent spinal cord, producing severe trauma and swelling that renders the spinal cord at that segment nonfunctional. Before ordering radiographs, the veterinarian must localize the area of the spinal cord where the trauma is most likely to have occurred. In this way, the radiograph can be focused directly over the suspected site with the vertebrae lined up to allow a better view of disc material in the spinal canal and any narrowing of the affected disc space. Gretchen's veterinarian tested some somatic reflexes—withdrawal and crossed extensor among them—in the hind limb and determined that the reflexes that travel through segments of spinal cord caudal to L3 were all hyperreflexive. This indicated that the reflex arcs were functional but were not being dampened by the upper CNS. Therefore the veterinarian could conclude that these spinal cord segments were caudal to the spinal cord trauma. The reflex arcs that traveled through L1, L2, and L3 were all hyporeflexive or nonexistent. The reflex arcs at these spinal cord segments were broken because of the trauma to the spinal cord segments. The reflexes that involved spinal cord segments cranial to T13 were normal, so these spinal cord segments were unaffected and still had communication with the upper CNS. The veterinarian ordered the radiographs centered over L2 on Gretchen. The radiographs indicated narrowed disc space between vertebrae L1 and L2. Because Gretchen's owner rushed her in quickly, the veterinarian could arrange emergency surgery to relieve the pressure on the spinal cord by removing part of the vertebral bone over the affected areas. Gretchen slowly recovered over several days, until she could walk with 90% of her normal strength and control.

Blood Volume

Here's the question. How do you know if you can draw 200 ml of blood from an animal to use in a blood transfusion without causing serious problems? Our limit will be 25% of the total blood volume, which is more blood than you would routinely draw from an animal, because an animal that loses 25% of its total blood volume has about a 50 : 50 chance of survival, but let us examine a worst-case scenario. First, you need to know how much blood an animal has. The total blood volume for any animal can be estimated using the animal's lean body weight. Lean is the operative word here. A 13.5 kg (30 lb) house cat is not lean. Therefore if you want to figure the total blood volume for this cat, think of it as a 3.5 to 4.5 kg (8 to 12 lb) cat. As a broad rule of thumb, figure 50 to 100 ml (average 75 ml) of blood/kg lean body weight. Highly strung animals tend to have more blood volume because they are always active—pacing, bouncing, and running—so they need more oxygen in their muscles. Using these guidelines, a 454 kg (1000 lb) horse will have a total blood volume of about 34,000 ml or 34 L (454 kg × 75 ml of blood/kg = 34,050 ml total blood volume). Taking 200 ml of blood from this horse would result in a blood loss of 0.5% of the total blood volume (200 ml divided by 34,000 ml and multiplied by 100 to get a percentage). Not a problem. Now let's consider a 16 kg (35 lb) dog with a total blood volume of 1193 ml. Drawing 200 ml from this dog would result in a blood loss of 16%. This is still not a problem, but we're getting closer to trouble.

Hyperthermia and Protein Denaturation

Hyperthermia is the scientific name for elevated body temperature, and it can have many causes such as a fever, heatstroke, or prolonged seizures. When the body temperature becomes too elevated for too long, the chemical bonds between and within molecules start to break. The hydrogen bonds holding proteins in their tertiary and quaternary structures are especially sensitive to this stress. When these bonds break, proteins are released from their complex structures and stretch into a straight chain of amino acids. Because they no longer have their unique shape these proteins lose their function. This is called the denaturation of proteins. Once this happens on a large scale it is irreversible, and the tissues of the body are irreversibly damaged. Some body proteins denature at 40° C (104° F), and death will usually occur around 41.7° C (107° F) if that temperature is maintained for 30 minutes.

Vasectomy

If a section of each vas deferens is removed surgically from an animal, the animal is rendered sterile (it cannot reproduce). This procedure is known as a vasectomy. It prevents spermatozoa from reaching the urethra during ejaculation. The other components of semen are ejaculated, but no spermatozoa are included. The individual is "firing blanks," so to speak. The spermatozoa live out their lives in the epididymis, die, and are absorbed by the lining cells. Vasectomy is a common contraceptive surgery to prevent pregnancy in humans. It is performed less commonly for that reason in nonhuman animals but is sometimes performed on bulls to create "teaser" animals. Teaser bulls are used to help identify cows in heat so that they can be bred, often by artificial insemination, to other males.

Postprandial Lipemia

If an animal has eaten just prior to a blood sample being drawn, the plasma may appear cloudy owing to fat from the digested food suspended in the plasma. This condition is referred to as postprandial lipemia (postprandial means after eating, and lipemia means fat in the blood), and it can make the plasma or serum unsuitable for laboratory analysis, depending on the analytic method used. For this reason, blood samples for laboratory analysis should be drawn before an animal is fed or a couple of hours after feeding.

Neutropenia and Leukocytopenia

If an infection is out of control, all the reserves of neutrophils can be used up faster than the bone marrow can replace them. If this happens, the number of neutrophils in circulation decreases, because the neutrophils are leaving the bloodstream and entering tissue, and there are no cells in the bone marrow to replace them. This condition is called neutropenia. The total white blood cell count will also decrease. This is leukocytopenia. The prognosis is poor for an animal that is clinically ill with accompanying neutropenia and leukocytopenia. It means the body is losing the war against the invading microorganisms.

Chromosome Combinations

If you want to do some interesting mathematical calculations, determine how many different combinations of chromosomes could result for different species by randomly assigning one of each pair of diploid chromosomes to each reproductive cell. Hint: Because the diploid chromosomes occur in pairs, you can start with the number 2 and multiply it times itself as many times as there are pairs of chromosomes. For example, a diploid chromosome number of 8 would have four pairs of chromosomes, so the number of possible haploid chromosome combinations would be 24, or 16 possible combinations. Try using that calculation for some of the diploid chromosome numbers listed in Table 19-1. (Divide the diploid chromosome number in half and multiply 2 by itself that many times.) You are going to get some very large numbers. Those large numbers represent the number of possible combinations of chromosomes that could occur in each spermatozoon or ovum from an animal of that species. If you want to calculate the number of chromosome combinations possible in an offspring of that species, you need to take the number of possible chromosome combinations for a spermatozoon and multiply it by the number of possible chromosome combinations for an ovum: you are going to come up with some ginormous numbers. In a human, for example, the diploid chromosome number is 46, so the number of possible combinations of chromosomes in each spermatozoon or ovum is 223, or 8,388,608. The number of possible combinations of chromosomes in a human infant would then be 223 × 223, or 70,368,744,177,664. Barring an identical twin, the chance of your parents producing a brother or sister with the exact same chromosome combination as you is 1 in 70,368,744,177,664!

Defibrillation

If you've watched a few hospital shows on television, chances are you've seen someone grab a couple of paddles, yell "clear" or something like it, place the paddles on the patient's chest, and "shock" them to restart the heart. In real life, this process is called defibrillation, and it has to do with the electrical conduction system of the heart. Sometimes a diseased heart will develop one or more ectopic pacemakers. The word ectopic means out of place, and an ectopic pacemaker is located outside the heart's normal pacemaker, which is the sinoatrial (SA) node in the right atrium. Despite the presence of any ectopic pacemakers, the SA node continues to fire, meaning that the cardiac muscle cells receive electric currents from more than one direction. The synchronized contraction of the heart, which begins in the atria and flows through the ventricles, is lost. If there is enough ectopic pacemaker activity, a condition called ventricular fibrillation may develop, in which heart muscle cells in different areas contract independently of one another. In ventricular fibrillation, all coordinated pumping activity of the ventricles is lost. The defibrillator sends a large electric current of short duration through the heart, with the objective of repolarizing all of the cells at the same time. If defibrillation is successful, the SA node and the heart's normal conduction system will resume control over depolarization of the heart after the cells have been "reset" by defibrillation.

What Are IMHA and ITP?

Immune mediated hemolytic anemia is a immune malfunction where the body destroys its own red blood cells (RBCs), either by creating antibodies directed at its own RBCs, or by IgG and complement binding to the RBCs marking them for destruction. There are two types of IMHA, primary and secondary. Primary IMHA occurs when the body creates antibodies directed at its own RBCs. Secondary IMHA occurs when foreign proteins bind to RBC membranes (e.g., FeLV in cats, vaccines, Ehrlichia canis infection, toxins, zinc toxicity, onion toxicity, or heartworm infection). A diagnosis of IMHA is based on a combination of clinical signs and diagnostic test results. Patients typically present with lethargy, weakness, pale mucous membranes, icterus, hematuria, bruising/petechiae, and possibly vomiting and diarrhea. Examination often shows hepatosplenomegaly, due to removal of increased numbers of destroyed RBCs from circulation. Icterus is caused by the excess destruction of RBCs, which releases more bilirubin into the bloodstream than the liver can conjugate. This results in the bilirubin being deposited in skin and mucous membranes and giving them a yellow tinge. Blood tests will show hyperglobulinemia (excessive antibodies in the circulation, indicating an active immune system), hyperbilirubinemia, anemia, reticulocytosis (increase reticulocyte count, indicating regenerative anemia), and the presence of spherocytes (small RBCs lacking an area of central pallor). Treatment consists of identifying the underlying cause of the IMHA (if any), and treatment with an immunosuppressant drug, such as prednisone, which acts to decrease the activity/sensitivity of the immune system and stop destruction of the RBCs. ITP is a decreased thrombocyte (platelet) count, which often is seen concurrent with IMHA. The two conditions are often seen together because the same mechanism (destruction of self cells) causes both. When ITP is present, the animal may also have impaired clotting abilities that need to be taken into account when caring for the animal (blood draws, injections, and so on). Treatment for ITP is similar to the treatment for IMHA.

Hardware Disease

In cattle, the reticulum (the most cranial stomach compartment) rests directly behind the heart, and the two organs are separated by the muscular diaphragm. Cattle are not very selective when eating, and it is not uncommon for them to ingest wires, nails, and other foreign metallic objects along with their feed. These bits of "hardware" are ingested into the rumen, from which digestive contractions move them forward into the reticulum. Continued ruminal contractions, particularly when combined with factors that increase abdominal pressure, such as pregnancy and parturition, may push pieces of wire through the cranial wall of the reticulum. Puncture of the reticulum wall by a foreign object often results in traumatic reticuloperitonitis, also called hardware disease, which is an inflammation and infection of the reticulum and abdominal cavity. More severe disease occurs when a wire is pushed even farther cranially, through the diaphragm and into the pericardium. This can result in septic pericarditis, which is an infection of the pericardium that usually progresses to heart failure and death. Hardware disease can be prevented by the oral administration of a magnet about the size of a 5 ml blood tube. The magnet stays in the rumen or reticulum, usually for the rest of the animal's life. Wire or other metal objects ingested by the animal stick to the magnet instead of being pushed cranially through the wall of the reticulum and beyond.

The Anticlinal Vertebra

In most veterinary practices, dogs are the animal species in which intervertebral disc disease is most commonly seen. As a result, veterinary personnel take a lot of spinal radiographs of dogs. The bones of the spine can be confusing to look at. When trying to identify the precise location of a lesion, the anticlinal vertebra is a convenient landmark. The eleventh thoracic vertebra, T11, is called anticlinal because its spinous process, unlike those of the surrounding vertebrae, projects straight up. The spinous processes of the first 10 thoracic vertebrae all recline caudally, and the last two, T12 and T13, incline cranially, so T11 looks out of place and is easily identified. The anticlinal vertebra in cats is also T11, but in horses it is T16; in cattle and sheep it is T13, and it is T10 in swine.

Congestive Heart Failure

In older dogs, congestive heart failure (CHF) is a fairly common problem. CHF occurs when the pumping ability of the heart decreases, usually due to disease of the heart muscle or a valve malfunction that restricts the forward flow of blood through a valve or allows a backward flow. CHF may be predominantly right-sided or left-sided. When the right side of the heart begins to fail, blood returning from the systemic circulation is no longer able to move through the right heart as quickly. This causes increased blood pressure in the systemic circulation, which results in fluid accumulation in the form of ascites (fluid in the abdomen) and edema (fluid in the tissues). When the left side of the heart fails, venous return from the lungs is decreased, resulting in pulmonary edema, which interferes with respiratory function. The decrease in cardiac output associated with heart failure may also reduce perfusion of important organs, such as the kidneys, to dangerously low levels. Medications used to treat CHF include cardiac glycosides to increase the strength of cardiac contractions, diuretics to promote elimination of extra fluid to relieve edema, and vasodilators to enhance blood flow to the organs and decrease vascular resistance to outflow from the heart. CHF in pets cannot be cured, but it can often be medically managed to improve the animal's quality of life.

Autoimmune Diseases

In some instances, the immune system malfunctions and starts seeing "self" as "not self." In other words, part of the animal's own body becomes recognized as foreign. This results in a classification of diseases known as autoimmune diseases. For example, autoimmune hemolytic anemia (AIHA) is a disease in which the animal starts producing antibodies against its own red blood cells. The antibodies cling to the red blood cell membranes and cause the cells to clump together (agglutination). These clumps of cells are detected by the tissue macrophages in the spleen, removed by them, and destroyed. If enough red blood cells are removed this way, the animal will become anemic.

Light Microscopy

In the 1600s, a Dutch scientist named Anton van Leeuwenhoek found microscopic creatures in pond water. He was able to make this exciting discovery using a single-lens microscope that he had fabricated himself. The Englishman Robert Hooke also made his own microscope, which allowed him to observe the tiny units that make up cork. These early, homemade tools were the first light microscopes and marked the beginning of three and a half centuries of impressive exploration in the frontiers of microspace. Light microscopy works by using visible light to see tiny structures. Tissues and other items being examined are sliced or spread out into thin layers, affixed to glass slides, and stained. When placed on the stage of the microscope, as shown in the drawings below, the tissues can be examined through the ocular lens. Light comes from underneath the slide and is concentrated on the tissue by the condenser. The effect of this backlighting is dramatic and colorful. Pictures taken of microscopic objects using a light microscope are called light micrographs and are found throughout this and other anatomy texts. Use of stains, including fluorescent stains, has markedly improved the visibility of microscopic structures using light microscopy.

Rosalind Elsie Franklin

In the early 1950s, when research on heredity was moving forward rapidly, Dr. Rosalind Franklin, at King's College in Cambridge University, used crystal chromatography to study the structure of DNA. She made meticulous preparations and produced several excellent photographs. One in particular, photograph 51, showed the helical structure of the molecule. Without her permission, Maurice Wilkins, who worked with Franklin in the same laboratory, showed her data and photograph 51 to James Watson and Francis Crick. Immediately, Watson and Crick began work on a new 3-dimensional model that included two helical strands, discarding their previous 3-helix model. On March 17th, 1953, Franklin wrote a draft paper based on her own research describing the structure of DNA and detailed the placement of the sugars, phosphates and nitrogenous bases. However, before her paper was published, James Watson and Francis Crick's paper appeared on April 25, 1953 in Nature. By the time Watson and Crick's paper was published, Franklin had left King's College for a new appointment at Birkbeck College, where she was given charge of a new research group working on the tobacco mosaic virus. At Birkbeck, Franklin found a collaborative working environment in which she became highly productive. She enthusiastically initiated work on the structure and assembly of the tobacco mosaic virus and, during the four and a half years she spent at Birkbeck, published 17 papers. This was an impressive feat in the best of circumstances, but was particularly so for Franklin, because in 1956 she was diagnosed with ovarian cancer, which may have been caused by her lengthy exposures to x-ray radiation. Despite her illness, she maintained an arduous schedule and continued working in the laboratory until shortly before her death two years later. She died in London on April 16th, 1958 at the age of 37. After her death, her colleague Aaron Klug, who had been working with Franklin since 1954, took over the directorship of the laboratory at Birkbeck. He continued the research that Franklin had started on the tobacco mosaic virus and completed new research on the polio virus. Klug was subsequently awarded the Nobel Prize for this work. In 1962, four years after Rosalind Franklin's death, the Nobel Prize for Medicine or Physiology was awarded to Francis Crick, James Watson, and Maurice Wilkins for determining the structure of DNA. Regrettably, the Nobel Prize is only awarded to the living. Nominations cannot be made posthumously. The premature death of Rosalind Franklin arguably robbed her of two chances to win the Nobel Prize herself. Nevertheless, it is widely felt that her contribution to the discovery of the structure of DNA is comparable to those who did receive the prize, and that she is indeed among the most brilliant scientists of our time.

Insulin

Insulin is an important ligand that binds to specific receptors on the surface of cells, particularly liver, fat, and cardiac and skeletal muscle cells. Insulin stimulates glucose uptake by triggering the movement of glucose transporter protein 4 (GLUT4) from an intracellular storage compartment to the plasma membrane. Once inside the cell, glucose is used to manufacture adenosine triphosphate (ATP), a vital energy source that fuels metabolic functions. Without adequate amounts of ATP the cell may not be able to function properly, can weaken and may even die. In many patients with type 2 diabetes (also known as diabetes mellitus), the number of insulin receptors on the cell surface is decreased. This is a physiologic response to excessive fat stores in the animal and is one form of insulin resistance. With fewer insulin docking sites in the cell membrane, diminished amounts of glucose are brought inside the cell. Paradoxically, the cell begins to starve even though the level of glucose outside the cell is very high (too high).

An Easy Diagnosis

It is not uncommon for cats or dogs to develop Horner's syndrome, a condition caused by damage to a chain of nerves that extends from the chest, up the neck, and into the head and face. Possible causes include ear infections, particularly those caused secondarily by ear mites; trauma to the neck, often from misuse of choke chains; tumors in the chest; and trauma to the nerves in the armpit region. Usually only one side of the face is affected, and the most pronounced clinical signs include abnormal changes to the affected eye. Horner's syndrome also causes profound dilation of blood vessels in the muscles and skin of the face, an abnormality that is obvious in horses because they sweat profusely on the affected side. However, in domestic dogs and cats that do not sweat this change is usually not clinically apparent. In Siamese cats, the increased blood flow and the increased temperature in their faces change the shape of thermolabile enzymes, making them unable to function normally. The production of pigment in the hair is halted, and in cases of long-term Horner's syndrome, the characteristic dark brown or black color of the Siamese face fades to a light tan or buff. Keep in mind that the appearance can look comical, because this condition usually affects only one side of the face. Fortunately, for most cats, Horner's syndrome is a short-term disorder.

Hematocrit and Packed Cell Volume

One of the most important diagnostic screening tests performed on blood is the packed cell volume (PCV), also known as the hematocrit. An anticoagulated blood sample is placed in a small tube and centrifuged at a high speed. This causes cells with a higher specific gravity to settle in the bottom of the tube whereas the plasma, with its lower specific gravity, stays on top. The red blood cells that settle on the bottom will make up 28% to 55% of the sample volume, depending on the species. The height of the column of red blood cells is measured in proportion to the height of the entire sample, which allows the percentage of red blood cells to be determined. This value is called the packed cell volume and is expressed as a percentage. The PCV is a useful test to screen a patient for anemia. The percentage of red blood cells will be smaller if the animal is low on red blood cells or if the red blood cells are smaller than normal, two of the causes of anemia. The PCV can also be used to screen for patient dehydration, which causes relative polycythemia and hemoconcentration because the red blood cells are suspended in less plasma. Even though most people use the terms packed cell volume and hematocrit interchangeably, there is a technical difference. The hematocrit is determined by automated hematology analyzers that actually count the number of red blood cells per specific volume of whole blood sample. The hematocrit is also expressed as a percentage of red blood cells in a blood sample, but it is considered more accurate because the red blood cells are counted directly by the analyzer. When a centrifuge is used, we must rely on the efficiency of the centrifuge to pack the cells tightly enough to squeeze all the plasma out from between the cells, but not so tightly that some of the cells rupture. Because of this difference in procedure, sometimes there is a discrepancy between the packed cell volume reported from a centrifuged blood sample and the hematocrit reported from an automated hematology analyzer.

Laminitis: A Painful Health Risk to Horses

Laminitis, or founder as it is commonly called, is an excruciatingly painful disorder that affects the feet—primarily the front feet—of horses and ponies. As its name implies, laminitis is inflammation of the delicate laminae that attach the hoof wall to the underlying coffin bone. As with all inflammation, laminitis involves swelling; however, the outer wall of the hoof is rigid and cannot expand to accommodate the swelling of the inner foot, so the laminae become compressed. Blood flow and circulation within the foot are inhibited, and the laminae degenerate. Because the laminae attach the coffin bone to the outer hoof, their degeneration may cause the distal phalanx or coffin bone to pull away from the hoof wall. Under the weight of the animal, the bone may rotate downward and push against the sole of the hoof. With very severe rotation, the distal phalanx can actually perforate the sole, and this will lead to the death of the animal. Chronic laminitis causes abnormal hoof growth. 169 Because laminitis is acutely painful, affected animals are often recumbent for extended periods, standing only to urinate, defecate, and access water and food. When standing, horses with laminitis tend to shift their weight away from the front feet to their hind legs to alleviate pressure in the toe. Their gait is slow and hesitant, and their heart rate and respiratory rate may be elevated because of the pain. A mild tap on the toe with hoof testers can elicit a strong pain response from the horse. In cases of chronic laminitis, external changes to the hoof become evident. Circumferential rings in the outer hoof wall become pronounced, marking previous aberrations in hoof growth. The angle of the hoof is reduced, and the hoof consequently appears flattened. If rotation has occurred, the sole may appear "dropped." With corrective trimming of the hoof, change in diet, and good management techniques, some of these aberrant changes can be corrected. Predisposing factors for laminitis include the following: • Engorgement of foods high in carbohydrates • Any systemic illness or condition that might lead to endotoxemia • The postoperative period • Retained placentas in mares • Adverse reaction to drugs Ponies, in particular, are prone to developing laminitis, particularly if they are permitted to graze on lush pasture or are fed diets rich in carbohydrates such as corn, molasses, and grains. Treatment is designed to decrease swelling, relieve pain, and increase circulation in the feet. Prevention by adherence to a strict, low-carbohydrate diet is essential in ponies and horses that are sensitive to carbohydrate levels.

Fluid Therapy: A Case Scenario

Leonard is a 2-year-old male castrated Yorkshire Terrier that has vomited six times in the past 36 hours. The owner says that Leonard has been sleeping more than usual and did not want to go for a walk as he normally does. After examining the patient, the veterinarian recommends that Leonard be hospitalized, given fluid therapy, and have further testing performed. The physical examination findings include the following information: Leonard weighs 10 lb (or 4.5 kg). His skin has lost some of its turgor and his gums are tacky. You 79estimate the percentage of dehydration to be about 8%. As you prepare to administer intravenous fluids, you make the following calculation: 1. Fluid losses from dehydration: 4.5 kg × 0.08 × 1000 = 360 ml. 2. Ongoing fluid losses from vomiting: 40 ml × 6 = 240 ml × 2 = 480 ml. 3. Maintenance fluid needs: 132 × (4.5kg)(0.75) = 408 ml. 4. Total replacement fluids: 360 + 480 + 408 = 1248 ml = 1.25 L. 5. Hourly rate = 1248 ml/36 hours = 35 ml/hour. After 36 hours, Leonard is rehydrated, and the rate per hour is decreased. Maintenance fluids and ongoing fluid losses are combined to estimate the lower rate.

Local Anesthetics

Local anesthetics are drugs that are injected into superficial areas of the body to block the conduction of sensations from that area. You may have experienced this form of anesthesia if your dentist administered a local anesthetic to numb an area of your mouth. Local anesthetic drugs such as lidocaine prevent sensory nerves from depolarizing despite stimulation from the dental or surgical procedure. If these sensory nerves do not depolarize, the brain is unaware of any sensation from that area of the body, therefore you do not feel pain. Lidocaine prevents the sensory neuron from depolarizing by blocking the sodium channels through which sodium ions usually flood into the neuronal cell. If the sodium channels are plugged by the local anesthetic molecule, no sodium can flood into the cell despite the channels being stimulated to open. No sodium influx means that no positive charge occurs in the neuron, threshold is not attained, and the stimulus is not turned into a depolarization wave. Any nerve impulse that has been generated stops at that point. Anesthesia means without sensitivity. If a sensory nerve does not depolarize, the animal's brain does not perceive sensations from that area of the body. Local anesthetics are used not only to anesthetize areas of the body for minor surgical procedures, but also to aid in identifying sources of pain that cause lameness in horses. In a lame horse, a local anesthetic may be injected around selected sensory nerves to prevent them from transmitting impulses. If injection around a particular nerve improves the horse's movement or reduces the lameness, the veterinarian knows that the source of the problem is in the area of the leg or hoof whose sensations are supplied by the "blocked" nerve. If the "nerve block" does not improve the lameness, the veterinarian injects another specific sensory nerve and repeats the process until the horse appears to have less pain.

Immune Mediated Hemolytic Anemia

Lucy, a 23 lb, 7-year-old female spayed Cocker Spaniel, presented with acute lethargy/weakness, anorexia, exercise intolerance, and hematuria. According to her owner, Lucy was vaccinated 3 weeks prior to the onset of clinical signs. Lucy appeared depressed in the exam room and was quiet, but alert and responsive. Based on the diagnostic test results the veterinarian diagnosed Lucy with immune mediated hemolytic anemia (IMHA) and autoimmune thrombocytopenia (ITP), likely secondary to vaccination. Lucy was hospitalized and placed on intravenous (IV) fluids, glucocorticoids (to prevent destruction of red blood cells and suppress the overactive immune system), and was given a transfusion of whole blood to treat anemia. Patients with IMHA and thrombocytopenia may have coagulopathies, which will interfere will blood clotting, so a large vessel like the jugular vein should not be used to draw blood samples. Caution stickers were also placed on Lucy's cage stating "NO JUGULAR BLOOD SAMPLES."

Chemotherapeutic Drugs

Many drugs are currently used to fight cancer in animals. These drugs are called chemotherapeutic drugs, and they work by blocking cell division and protein synthesis. With such treatments the cancerous cell cannot repair itself or divide, and it subsequently dies without leaving behind daughter cells. Chemotherapeutic drugs may be either specific for a certain phase of cell division or nonspecific, affecting all phases of cell division. These drugs are particularly effective against rapidly dividing cells, such as tumor cells, but may affect rapidly dividing normal cells as well. For example, cells that line the intestinal tract, young blood cells that form in bone marrow, and the active cells in hair follicles are all normal cells that are often affected by chemotherapeutic drugs. Therefore it is not surprising that some of the side effects of chemotherapy include nausea, diarrhea, hair loss, and decreased production of blood cells. Unfortunately, some tumors that do not grow quickly are not as affected by chemotherapeutic agents. In these cases, chemotherapy may need to be extended for long periods, or the veterinarian may consider using other forms of cancer treatment, such as surgery and radiation therapy. Some chemotherapeutic drugs are extremely toxic to the tissues that lie outside of blood vessels, so technicians must be very careful when administering the drugs intravenously. Placing a catheter in the vein is a good way to ensure that the chemotherapeutic agent is administered properly. Extravascular administration of vincristine, for example, will cause necrosis (tissue death) and sloughing of the perivascular tissue. Any attempt to irrigate the tissue or dilute the drug by injecting saline only spreads the drug, increasing the amount of tissue that will subsequently die. There are six major classes of chemotherapeutic drug: alkylating agents, antimetabolites, plant alkaloids, antibiotics, hormonal agents, and miscellaneous agents. How Do They Work? Alkylating agents such as cyclophosphamide (Cytoxan), cisplatin (Platinol), carboplatin (Paraplatin), chlorambucil (Leukeran), and melphalan (Alkeran) stop cell division by causing strands of DNA to cross-link and, in doing so, they inhibit DNA replication because a cell cannot divide or make proteins if the DNA is abnormally linked together. Without the necessary proteins and enzymes required for metabolic function, the cell quickly dies. The antibiotic doxorubicin (Adriamycin) works in a similar manner, as it binds DNA and inhibits mitotic activity. Antimetabolites such as cytosine arabinoside, 5-fluorouracil, and methotrexate are analogs of the DNA bases purine and pyrimidine. Antimetabolites are incorporated into the DNA molecule during DNA replication and subsequently inhibit protein and enzyme synthesis. Plant alkaloids, such as vincristine, are phase specific and affect only the M phase of the cell cycle by inhibiting mitosis. Plant alkaloids bind to the proteins in microtubules 101and interrupt the formation of the mitotic spindle. Without a spindle, the chromosomes cannot be separated properly, cell division is halted, and the cell subsequently dies. In high doses, corticosteroids, such as prednisone and prednisolone, interfere with the cell division of lymphocytes. This lympholytic activity makes them particularly useful in treating lymphoid cancers such as lymphoma. They have an added benefit of increasing appetite and therefore are often used in conjunction with other chemotherapeutic agents. The best known miscellaneous agent in veterinary use is asparaginase, which, as its name implies, is an enzyme that breaks down asparagine, an amino acid used by cancer cells. It has no effect on normal cells and usually is used in combination with other chemotherapeutic drugs.

Neutrophils and the Stress Response

Neutrophils can move freely between the circulating and marginal pools. At any given time, in dogs, cattle, and horses, there is about a 50 : 50 ratio between the number of neutrophils in the circulating pool and the marginal pool. In cats, the ratio is about 30 : 70. Cells can detach from the marginal pool and enter the circulating pool when an animal is experiencing some sort of physical or mental stress. Trauma, fear, and exercise are a few of the stresses that may lead to a temporary transfer of neutrophils from the marginal pool to the circulating pool. This predictable neutrophil response is part of a larger physiologic reaction called the stress response. Splenic contraction also plays an important role in this movement of cells out of the marginal pool. The temporary movement of neutrophils into the circulating pool can artificially elevate the total neutrophil count (neutrophilia) and the total white blood cell count (leukocytosis) because the normal values are based only on the number of cells normally found in the circulating pool. These artificially elevated results can lead to a possible misdiagnosis. Remember this when you have to chase a horse around a pasture or wrestle with a cat to get a blood sample.

Heatstroke and Hypothermia

Normal cellular functions in warm-blooded animals depend on the core body temperature remaining fairly constant. This is because chemical reactions, including all the metabolic reactions that occur in the body, are temperature dependent. Higher temperatures speed up chemical reactions, and lower temperatures slow them down. Significant variations in the core temperature of the body, such as might occur in heatstroke (significantly elevated body temperature) or hypothermia (significantly decreased body temperature), can have serious consequences and endanger the life of the animal. Heatstroke can result from prolonged exposure to high environmental temperatures. The core temperature of the affected animal climbs to dangerously high levels. Early on, the animal typically appears weak and confused; as things progress, it may lapse into unconsciousness that can lead to convulsions and even death. The very rapid heart and respiratory rates that occur in affected animals are signs of the abnormally accelerated metabolic reactions in the body. If the animal is not cooled in time, the distorted metabolic reactions, particularly in the brain, can reach a point at which brain damage and possibly death can result. The maximum body temperature compatible with life is about 10° F (5° C) above the animal's normal body temperature level. Hypothermia results from an abnormally low body temperature that slows all the metabolic processes. The heart and respiratory rates of affected animals slow as their core temperatures drop. If not warmed, affected animals can lose consciousness and die. Hypothermia can result from prolonged exposure to cold environmental temperatures, but it can also occur in the veterinary hospital in animals under general anesthesia. Most general anesthetic drugs anesthetize the temperature control centers in the brain along with the conscious mind. This often results in a slow fall in body temperature during anesthetic procedures that can be accelerated by contact with cold environmental surfaces, such as metal surgery tables. The falling core temperature slows metabolic reactions in the animal's body, including those that metabolize or eliminate the anesthetic agent at the end of the procedure and allow the animal to wake up. This can prolong the time it takes for the animal to recover from the anesthetic. For this reason, we generally try to keep anesthetized and recovering animals warm through means such as table and cage warmers, towels, blankets, and hot water bottles.

Intervertebral Disc Disease

Normal intervertebral discs have a soft, cushioning center of gelatinous material called the nucleus pulposus, which is surrounded by tough fibrocartilage. On their sides and bottoms, intervertebral discs are surrounded by tough ligaments and dense muscles that support the spinal column and join the vertebrae together. The only thing dorsal to these discs is the spinal cord, which is tightly encased in the bony spinal canal. Intervertebral disc disease results when one or more discs degenerate. When a disc becomes diseased, normal mechanical forces on the spine often result in degenerated disc material being squeezed out. The ligaments and muscles on the sides and bottom of the disc prevent the material from moving in any of those directions, so the only direction it can protrude is dorsally, up into the spinal canal, where it presses on the spinal cord. Because the spinal cord is surrounded by bone, it has no way to escape the pressure when the protruded disc material compresses it, which causes the common clinical signs of intervertebral disc disease: pain, numbness, weakness, and paralysis. Intervertebral disc disease can occur in any species of animal but is seen most often in dogs, particularly long-backed breeds such as Dachshunds. It usually occurs in one of two sites: the cervical region or the thoracolumbar region. Cervical disc disease usually causes severe pain. The neck muscles go into spasm, and the animal holds its head and body very rigidly and does not like being touched. Disc disease in the mid back usually causes weakness, sometimes called paresis, and numbness of the hind legs that can progress to complete paralysis. Treatment options include exercise restriction or cage rest, medical treatment with drug therapy to reduce pressure on the spinal cord, and surgery to decompress the spinal cord directly. The prognosis depends on the location, extent, and duration of the damage to the spinal cord. Author's note: I once had a Dachshund patient with thoracolumbar disc disease whose rear legs remained paralyzed despite weeks of intensive treatment. The dog's owners reluctantly decided to euthanize him and have him buried in a nearby pet cemetery. The afternoon before the scheduled euthanasia, a representative from the pet cemetery came to our hospital to measure the dog for a coffin. This apparently got his attention, because the next morning, when the time came to do the regrettable deed, we noticed some slight rear-leg movement. We canceled the euthanasia and the dog went on to make a full recovery. Apparently, he had only needed the proper motivation.

Patellar Luxation in Dogs

Normally the patella rides securely in the deep groove of the trochlea on the distal end of the femur. The pull of the quadriceps tendon is normally directly in line with the trochlea. Sometimes physical abnormalities cause the pull of the tendon to be off-line, or one rim of the trochlear groove may not be high enough to hold the patella securely in place. When that occurs, the patella can luxate or pop out of the trochlea, usually toward the medial side. The most common type of patellar luxation occurs in small and miniature dog breeds and results in the patella popping out of the medial side of the trochlear groove when the foot is planted. This causes pain when the animal tries to flex the stifle joint to take its next step, and so it will often carry or hold up the affected leg for a step or two until the patella pops back into place. This causes a periodic, skipping-type gait that is characteristic of this disorder. The condition is easily diagnosed by extending the stifle joint and palpating the easily displaced patella. Treatment usually consists of any of several types of surgical correction.

Vaccination Protocols 1

Occasionally a client will come into a veterinary clinic and ask to have a pet vaccinated so it can go to the groomer, boarding facility, or daycare facility. Or a client wants some livestock vaccinated so it can be shipped across a border that same day. It is important for clients to understand that although vaccines will protect their animals from disease, the protection is not immediate. Vaccines stimulate the immune system (active immunity), but it takes time, usually about 2 weeks. As veterinary technicians, we need to help educate clients so they can help keep the animals in their care healthy and up to date on vaccines.

Sertoli Cell Tumor

On occasion, Sertoli cells can multiply out of control, particularly in dogs. This produces what is termed a Sertoli cell tumor in the testis. Because normal Sertoli cells produce small amounts of estrogens, this action can become exaggerated as the cells multiply out of control. The level of estrogens in the animal's bloodstream rises rapidly, producing feminization of the male dog. The prepuce often becomes pendulous, and the mammary glands may become enlarged (gynecomastia) and can even produce milk. The penis and the opposite testis atrophy, and other male dogs may be attracted to the affected animal as if he were a female in heat. The signs of feminization are often the primary complaints when affected animals are presented to the veterinary clinic. The primary treatment for a Sertoli cell tumor is usually castration of the animal.

The Sympathetic Nervous System Response to Shock or Blood Loss

One of the key roles of the sympathetic nervous system is to maintain arterial blood pressure. The arterial blood pressure can drop to a point where the brain may not be receiving adequate blood flow in situations involving a loss of blood volume; a loss of fluid in the blood, as with dehydration; or a large-scale dilation of blood vessels throughout the body, as in the case of shock. The body responds to this loss of arterial blood pressure by causing massive stimulation of the sympathetic nervous system. The heart pounds rapidly and fiercely in the chest to increase the output of blood into the arteries; simultaneously, the small blood vessels, or arterioles, in the skin, GI tract, kidney, and other areas constrict. The increased cardiac output and arteriole vasoconstriction result in an increased arterial blood pressure and more blood directed to the brain. The increase in blood arterial pressure from the increased cardiac output and vasoconstriction would be like the increase in air pressure within a rubber tube if you blew forcefully into the tube while simultaneously pinching the far end. The narrowing of the small blood vessels supplying the skin also explains why the skin and mucous membranes of people or animals with a sudden decrease in blood pressure appear so pale.

Otitis Externa

Otitis externa is an inflammation of the skin of the external ear canal that occurs most commonly in dogs, cats, and rabbits. It is often caused by parasites such as ear mites, foreign bodies, or microorganisms such as bacteria and yeasts. The irritation in the ear canal causes redness, pain, itching, and fluid accumulation. The owner usually notices that the animal shakes its head a lot and spends time scratching at its ears. When the affected ear is examined, the ear canal is usually red, moist, swollen, and painful, and often has a characteristic pungent odor. The basic anatomy of the external ear canal adds a challenge to the treatment of otitis externa. Gravity makes inflammatory fluids drain downward and accumulate in the horizontal portion of the canal next to the tympanic membrane. Because topical medications are usually part of the treatment of otitis externa, the ear canals must be cleaned thoroughly and carefully to remove discharges before the medications are instilled. Because the ear canals are often swollen and painful, this process can be difficult for at least the first few days. Therapy for otitis externa often must be continued for many weeks to bring the condition under control.

Ovariohysterectomy

Ovariohysterectomy is a surgical procedure in which the ovaries, oviducts, and uterus are removed from an animal. It is commonly known as spaying an animal. Despite the frequency with which it is performed, ovariohysterectomy is a major surgical procedure that involves opening the abdominal cavity. To remove the reproductive organs safely, the blood vessels supplying them must first be tied off (ligated). The blood vessels to each ovary are usually ligated along with the portion of the broad ligament (mesovarium) that contains them. This portion is referred to surgically as the ovarian pedicle or ovarian stump. The ovaries then can be severed safely from their ligated blood vessels. The remainder of the broad ligament is usually either ligated en masse or cut back toward the body of the uterus. The blood vessels in this part of the broad ligament are usually small. The body of the uterus and its accompanying blood vessels are ligated and transected (cut). The reproductive organs then can be removed safely from the abdominal cavity and the incision sutured closed.

Radiography Positioning Terminology

Radiographs, commonly called x-rays, are two-dimensional images of what is inside an animal. Radiographs are described according to the path the x-ray beam takes through the body using anatomic directional terms. For example, imagine a dog lying on an x-ray table on its back. The x-ray tube is above it, and the x-ray film is beneath it in a light-tight case called a cassette. During the exposure, the x-rays will enter the animal's ventral surface, pass through the abdomen, and exit the animal's dorsal surface before striking the film. We call this a ventro-dorsal (VD) view of the abdomen, because the x-rays enter the ventral surface and exit the dorsal surface of the body. A dorso-palmar (DP) view of a horse's front fetlock joint, which is the joint between the large metacarpal bone and the proximal phalanx, will have the x-ray machine positioned in front of the leg and the x-ray cassette behind the joint. The x-rays will enter the dorsal surface of the leg and exit the palmar surface. Lateral radiographic views are taken by passing the x-ray beam through the area of study from side to side. They are named according to which side of the animal is closest to the film. If the animal's right side is closest to the film for an abdominal radiograph, the view is called a right lateral view of the abdomen.

Renal Dysfunction and Uremia

Renal dysfunction is the term used to describe any pathologic condition that results in inability of the urinary system to remove waste materials adequately from the blood. When this happens, the waste materials, especially nitrogenous wastes from protein breakdown (e.g., BUN), build up in the blood and become toxic to the animal. The resulting condition is called uremia (literally "urine in the blood"). Uremia can be prerenal, renal, or postrenal. Prerenal uremia is associated with decreased blood flow to the kidneys and may be caused by conditions such as dehydration, congestive heart failure, or shock, if these conditions are left untreated. In these cases, the kidneys are functioning normally, but not enough blood is reaching them, so waste materials can't be adequately removed. Renal uremia is associated with an inability of the kidney to regulate urine production adequately because of damage to the nephrons (refer to the Clinical Application on feline chronic renal failure). Toxins, inflammation, or infections that localize in the kidneys and destroy nephrons are some of the causes of uremia due to kidney dysfunction. Even though there may be adequate blood flow to the kidneys, there are not enough functional nephrons present to regulate normal urine production, so waste materials can't be removed from the blood. The kidneys have far more nephrons than they need to function properly under normal conditions, so there is a large reserve of nephrons to take over if some of the nephrons are damaged or destroyed. Two thirds of the total nephrons in both kidneys must be nonfunctional before clinical signs of renal dysfunction start to become evident. Postrenal uremia is usually associated with an obstruction that prevents urine from being expelled from the body. Tumors, blood clots, or uroliths (stones) can cause the obstruction. Remember that urine is constantly being produced, even if it is prevented from being expelled from the body by the obstruction. Eventually urine will back up into the renal pelvis and then into the nephrons. This will result in increased pressure in the nephrons and kidney damage. Now it becomes a case of renal dysfunction, but the underlying cause was a postrenal obstruction. Uremia is diagnosed by evaluating a blood sample for the presence of increased amounts of waste materials. The easiest waste material to evaluate is urea, the nitrogenous waste product of protein breakdown. The amount of blood urea nitrogen (BUN) in plasma is an indication of how well the blood is being cleaned. Elevated BUN levels indicate a problem but will not distinguish among prerenal, renal, and postrenal uremia. Further diagnostic testing will be necessary to make that distinction.

Respiratory Tract Infections

Respiratory tract infections are common in all animals. However, a significant difference is noted between infections of the upper respiratory tract and infections of the lower respiratory tract. An upper respiratory tract infection (URI) affects some combination of the nasal passages, pharynx, larynx, and trachea. Although they can be severe, URIs are generally less likely to be life threatening than infections of the lower respiratory tract. The main reason is the body's ability to drain excess mucus and inflammatory fluids away from infected areas in the upper respiratory tract. The body can cough up the fluids, which are either expelled through the nose or mouth or swallowed. This kind of moist cough actually accomplishes something beneficial and is referred to as a "productive" cough. We usually don't want to suppress a productive cough, because it helps the animal. A lower respiratory tract infection is usually called bronchitis or pneumonia. As its name implies, bronchitis affects the lining of the bronchial tree. Pneumonia involves the tiny bronchioles and alveoli. In either case, the animal's condition is often more severe than with a URI because inflammatory fluids tend to accumulate deep in the lungs in the small, dead-end air passageways. The fluids are more difficult to cough up, and so they can accumulate and obstruct airflow. Lower respiratory tract infections can be very serious and sometimes life threatening.

Ununited Anconeal Process in the Dog

The anconeal process of the ulna develops from a secondary growth center that is separate from the primary growth center in the ulnar shaft. In dogs it normally fuses to the rest of the ulna by about 6 months of age. Sometimes, particularly in large and giant dog breeds, mechanical forces in the elbow break down the fusing tissues and prevent the anconeal process from uniting with the rest of the bone. This results in elbow joint instability that damages the joint surfaces and leads to secondary osteoarthritis, and the affected animal gradually becomes lame. The diagnosis can be confirmed by taking a lateral radiograph of the elbow in the flexed position, which will show the unattached process. Treatment usually involves surgical removal of the ununited anconeal process.

Metabolic Acidosis

Sometimes so much acid accumulates in the animal body that the buffering system is overwhelmed, and the pH of the blood is lowered. This condition is called metabolic acidosis. Two common causes are fatty acid accumulation in diabetes mellitus, due to the excessive breakdown of lipids for energy, and the accumulation of hydrogen ions in kidney disease caused by the kidney's inability to excrete them. In these conditions the blood and tissue have a high level of acid: weak acids from the buffering system and strong acids caused by the underlying condition. Metabolic acidosis can cause several uncomfortable and dangerous symptoms including anorexia, vomiting, lethargy, and muscle wasting. Severe metabolic acidosis can decrease cardiac output, reducing blood flow to the tissues, which further damages the kidneys and other organs. Life-threatening cardiac arrhythmias can also develop. Administering balanced electrolyte solutions treats metabolic acidosis since these fluids contain the buffers needed by the body to decrease the acid concentration in the blood.

Cranial Cruciate Ligament Rupture

Sometimes, particularly in dogs, a wrong step can result in a rupture or tearing of the cranial cruciate ligament (CCL), which is damaged more often than other ligaments. This injury can occur in athletic dogs if they plant a foot wrong while running and turning, or it can occur in overweight, sedentary dogs if they land wrong as they jump off the couch. The result is instability of the stifle joint. Instead of hinging on each other like they are supposed to, the femur and tibia also slide forward and backward relative to each other. This can damage other joint structures, such as the menisci, and can lead to osteoarthritis in the joint. Rupture of the CCL is diagnosed by palpating the stifle joint and producing what is called anterior drawer movement, which is an abnormal forward and backward movement of the femur and tibia relative to each other. Therapy for CCL rupture can range from exercise restriction, weight reduction, and physical therapy to any of several surgical repair techniques.

Taurine Deficiency in Cats

Taurine is an essential amino acid in cats and is found in high quantities in meat and fish, but it is virtually nonexistent in plant-based foods, including dog food. Therefore cats that are fed dog food or home-cooked vegetarian diets develop taurine deficiency after several months. The result is a progressive, irreversible retinal degeneration that ultimately leads to blindness. In addition, taurine deficiency has been associated with dilated cardiomyopathy, a condition in which the heart enlarges because of dilation of the cardiac chambers. In some cases, the walls of the ventricles become very thin and the ability of the heart to pump blood efficiently is altered. Cats may exhibit signs of heart failure, such as depression, shortness of breath, decreased exercise tolerance, and coughing. Fortunately, cardiomyopathy caused by taurine deficiency is reversible, and affected cats recover with nutritional supplementation. Queens that are taurine deficient may appear clinically normal but may have diminished reproductive success, including problems with abortion, early embryonic death, and malformations of neonates. An examination of the eyes of these cats usually reveals some degree of retinal degeneration. Kittens that are born to taurine-deficient queens and fed deficient diets often die. Those that do survive exhibit neurologic signs, including cerebellar dysfunction and paresis in the hind legs, which frequently splay outward. Occasionally, even cats that are fed diets adequate in taurine develop clinical signs of deficiency. In these cases, a biochemical disturbance in the retinal cells is thought to prevent normal taurine uptake and use.

The Clinical Patient and Healing

The Clinical Patient and Healing Some tissue types heal more readily than others. Epithelial tissues such as skin and mucous membranes heal rapidly but smooth muscle and dense regular connective tissue have limited regenerative ability. Cardiac muscle and nervous tissue in the brain and spinal cord regenerate extremely slowly if at all and are often replaced by scar tissue. In addition, some patients heal more easily than other patients. Old, immunosuppressed, debilitated, or sick animals heal more slowly than young, healthy, well-nourished animals. In this way, the age, overall health, and nutrition of patients are important factors in the rate and extent of healing. This is why elective surgery is avoided in unhealthy animals and why intravenous nutrition may be used in critically ill patients. Some diseased or otherwise stressed animals, for example, may produce too much cortisol, which can inhibit the animal's ability to heal; incision sites may take weeks rather than days to close, and wounds from even superficial injuries may become chronic nightmares. In addition, some drugs, such as prednisone, can also delay healing if blood levels are high. Thus the clinician must consider the overall health and medical history of an animal before carrying out any procedure that subsequently requires the healing of tissue.

Anesthesia and Analgesia

The ability to perceive sensations, or to feel things, is known as esthesia. (The study of the sensory system is called esthesiology.) Anesthesia is the loss of esthesia, or the complete loss of sensation. In clinical veterinary medicine, we use two basic types of anesthesia to carry out procedures that would be painful for patients: general anesthesia and local anesthesia. General anesthesia involves a complete loss of sensory perception accompanied by loss of consciousness. The animal is placed into a controlled sleep that prevents it from feeling painful procedures. We produce this sleep by administering general anesthetic drugs either by injecting them or by having animals breathe them from an inhalant anesthesia machine. Animals under general anesthesia must be monitored closely, because the drugs depress cardiovascular and respiratory functions along with the CNS. Local anesthesia produces loss of sensation from a specific, localized area of the body without affecting consciousness. It is produced by injecting a local anesthetic drug into an area through which sensory nerve fibers pass. The drug blocks the transmission of nerve impulses through the site, which prevents sensory information from reaching the central nervous system. This can allow potentially painful procedures to be performed without having to render the animal unconscious. Analgesia is a related state in which the perception of pain is decreased but not completely absent. The pain is dulled but not completely gone. A drug that produces analgesia is called an analgesic drug. Aspirin, carprofen (RimadylR), and morphine are all examples. Analgesic drugs are often used to make animals with severe pain (postsurgical patients for example) more comfortable.

The Blind Spot of the Eye

To detect the blind spot of your eye, mark an X on a piece of paper, and about 2 inches to the right of that mark an O. Now close or cover your left eye, focus your right eye on the X, and hold the paper about 12 inches from your face. Slowly move the page toward your eye. At some point, the O will disappear. When that happens, it has fallen on your optic disc, where there are no photoreceptors. So its image disappears! Interestingly, the brain normally fills in the blind spot area, so the conscious mind is not usually aware of that "hole" in the visual field.

Motion Sickness

The brain relies on the vestibular system, the eyes, and the proprioceptors around the body for information about how and where the body is moving so that it can keep the animal upright and maintain balance. Usually the information the brain receives from these sources agrees—the animal is either moving, or it is not. This is fine as long as it is standing or moving around on the ground (assuming the ground is not moving). But when we put an animal into a moving car, boat, airplane, or space vehicle, things become more complicated. The eyes look around the interior of the vehicle and see that nothing is apparently moving, but the equilibrium receptors and proprioceptors detect motion (or, in the case of space travel, the absence of gravity). This disagreement between the sensory receptors can result in the unpleasant sensations of motion sickness, such as headache, nausea, and vomiting. This often occurs in animals that travel by car, truck, boat, or plane. Medications often can be used to prevent motion sickness, but they usually must be administered before traveling. Motion sickness is easier to prevent than it is to treat in mid journey. Veterinary clinics may dispense anti-motion-sickness medications to clients who must travel with animals that are prone to motion sickness. A form of motion sickness is common in astronauts as well. Space adaptation syndrome occurs in a high percentage of astronauts, particularly during the first few days of a space flight. It causes symptoms similar to normal motion sickness, such as headache, nausea, and cold sweats. The symptoms often disappear after a day or two, indicating that the brain has adjusted to the conflicting signals. Ongoing research is focused on finding ways to prevent this annoying and sometimes debilitating disorder. It seems more complicated to deal with than traditional earth-bound motion sickness.

Unique Patients

The fact that each animal has an individual, unique genetic composition is not just hypothetical or interesting in an abstract sense. This uniqueness is an important concept for us to keep in mind as we examine and treat patients. It can significantly affect things such as behavior, clinical signs of disease, doses of drugs, and response to treatments. Even though all Golden Retrievers look a lot alike, a particular Golden Retriever we are working with may respond differently to our drugs and treatments than others of its breed we have worked with before. This is an important concept to grasp if we are to be effective in our work in clinical veterinary medicine. Each of our patients is an absolutely unique, original individual. It is reasonable to expect more similarities than differences among animals of a particular species and breed, but always keep in the back of your mind the possibility that this animal may not react exactly the same as others you have worked with in the past.

Pericardial Effusion and Cardiac Tamponade

The heart is able to expand and contract in the chest thanks to the layer of fluid that provides lubrication between layers of the serous pericardium. Normally, only a small amount of fluid is contained within the pericardial sac. A number of conditions such as infection, inflammation, or hemorrhage may cause excess fluid to accumulate in the pericardial sac. This condition is called pericardial effusion. Sometimes pericardial effusion is idiopathic, meaning it may occur spontaneously with no known cause. The outer layer of the heart, called the fibrous pericardium, is not elastic, so when the pericardial space is overfilled with fluid, the heart becomes unable to expand normally between contractions. This condition, called cardiac tamponade, leads to less complete cardiac filling, decreased stroke volume, and decreased cardiac output. Pericardial effusion, with or without cardiac tamponade, may be treated by inserting a needle into the pericardial sac (usually through the chest wall) and withdrawing the excess fluid.

Hypocalcemia

The hypocalcemia-preventing action of parathyroid hormone can sometimes be overwhelmed by the loss of calcium in the milk of lactating animals. The hypocalcemia that results can be a serious, potentially life-threatening condition. The most obvious clinical signs relate to disturbances in skeletal muscle function caused by the lack of calcium. In cattle this condition is called milk fever, and it results in generalized muscle weakness. In mild cases, tremors and weakness are seen. As the condition becomes more severe, the animal may lie down and be unable to rise. Such an affected animal is often referred to as a downer cow. In dogs and cats, the condition is called eclampsia; it can cause muscle tremors and spasms that can progress to full-blown seizures if left untreated. Treatment in both cases is aimed at rapidly increasing the level of calcium in the blood by infusing a calcium solution intravenously.

Recovery from General Anesthesia

The importance of head position to overall body posture and balance can be seen in an animal that is recovering from general anesthesia. One of the first things that a recovering animal tries to do as it regains consciousness is to raise its head into an upright position and steady it there. It has to get its head into that position before it can start trying to raise its body. Primitive instincts for survival prompt many animals to try and stand before they are steady and coordinated enough to support themselves. This can lead to stumbling and falling, which can cause injury. By taking advantage of our knowledge of the sense of equilibrium, we can prevent an animal from trying to get up prematurely by gently holding its head down in a horizontal position until it has enough strength and coordination to rise. This can be particularly important for larger animals, such as horses. By holding a recovering horse's head down with a gentle hand or knee on the dorsal part of its neck just behind the skull, we can keep the animal from trying to get up too soon. Once we feel it has regained enough strength, we can allow it to raise its head and prepare to help steady it as it rises to its feet.

Passive Immunity and Vaccinations

The passive immunity that newborns acquire from drinking colostrum is important to their early survival. However, it can interfere with early vaccinations, particularly in puppies and kittens. If a puppy or kitten is vaccinated while it still has a high level of antibodies from its mother in its bloodstream, the vaccine will be inactivated and will not stimulate the animal's immune system to manufacture new antibodies. So why not just wait until the passive immunity from mom wears off? The difficulty is that passive immunity lasts differing lengths of time in different animals. If you vaccinate too early, the vaccine is wasted. If you wait too long to vaccinate, the passive immunity may have worn off, leaving the animal susceptible to infection. The level of passive antibodies in the young animal's bloodstream can be tested, but this is expensive. The most practical solution is to give the young animal a series of vaccinations spread out over the period when protection from passive immunity is most likely to end. Specific vaccination protocols differ, but the first vaccination is usually given somewhere around 6 to 8 weeks of age, with subsequent vaccinations given every 2 to 3 weeks until the animal is 14 to 16 weeks old.

Ear Hematomas

The pinna of the ear consists of elastic cartilage and small blood vessels covered by skin. Sometimes irritation in the ear canal (such as with otitis externa) will cause an animal to shake its head vigorously (see the Clinical Application on otitis externa). In some animals, particularly floppy-eared dogs, this movement can rupture small blood vessels under the skin of the pinna, usually on the inside surface. The resulting bleeding between the cartilage and skin can cause an accumulation of blood, called an ear hematoma, which is an abnormal accumulation of free blood between the cartilage and skin of the pinna. An ear hematoma usually is not dangerous or even painful, but it is heavy and swollen and often seems to bother the animal. If left untreated, the blood will be reabsorbed slowly, but the ear probably will be permanently deformed by scar tissue, resulting in what is called a cauliflower ear. Treatment of ear hematomas usually involves surgically draining the material from the hematoma and placing sutures through the pinna to hold the skin tight against the cartilage and prevent fluid from reaccumulating. The underlying cause of the head shaking needs to be determined and treated also to prevent recurrence.

Homeostasis and Congestive Heart Failure

The processes in the body that try to maintain the functioning of a failing heart offer some excellent illustrations of how important homeostasis is as it attempts to maintain the health and life of an animal. Congestive heart failure is a clinical term used to describe a heart that is not pumping adequate amounts of blood. This results in blood "backing up" in the body, which produces congestion, or abnormal fluid accumulation, upstream from the failing heart. There are many causes and forms of congestive heart failure, but the overall homeostatic mechanisms that attempt to maintain normal blood circulation in the body are basically the same. The first indication that the heart is starting to fail is a drop in the cardiac output, that is, the amount of blood the heart pumps out per minute. The decreased blood flow and blood pressure are picked up by receptors in the vascular system and relayed to the central nervous system. Signals then go out to activate the sympathetic portion of the nervous system. This system, also called the fight-or-flight system, helps prepare the body for intense physical activity. Its effect on the cardiovascular system is to increase blood flow and blood pressure by stimulating the heart to beat harder and faster and by constricting blood vessels. In the short term, these mechanisms help bring blood flow and blood pressure back up to normal levels. Unfortunately, these compensatory mechanisms cause the weak heart to work harder, which is kind of like whipping an exhausted horse to get it to move faster or pull harder. The result is a further weakening of the heart and further decreases in cardiac output. This causes more sympathetic nervous system stimulation. The cycle continues to repeat until either the heart gives up completely or we intervene with medical therapy. Homeostatic mechanisms cannot change the basic defects that are causing the heart to fail, but they help the damaged heart maintain vital blood flow to the rest of the body for as long as possible. By adding good medical care to the body's natural homeostatic mechanisms, we can often extend the length and quality of life of an animal in congestive heart failure.

Canine Prostate Problems

The prostate gland in dogs is large—about the size of a walnut in a medium-size dog. Many conditions can cause it to become even larger, such as infection, tumors, or just normal aging. Because the urethra runs through the center of the gland, significant enlargement of the prostate squeezes the urethra. This can partially or completely block the passage of urine, leading to difficulty urinating. Instead of urine passing in a large stream, it dribbles out or may stop entirely. The cause of prostate gland enlargement must be determined to formulate an effective treatment strategy. Some conditions can be managed with medication, but others require surgery.

Sinusitis

The sinuses can be clinically significant if they become inflamed and swollen as a result of allergies, infections, tumors, and so on. If the openings into the nasal passages swell shut or become plugged with inflammatory debris, fluids in the sinus have nowhere to go, and the resulting buildup of pressure can be very painful for the animal. This condition is known as sinusitis. Sinusitis can often be treated effectively with drugs such as antibiotics to combat disease-causing microorganisms and decongestants to reduce the swelling in the lining of the sinus. However, in some severe cases, a hole must be surgically drilled into an inflamed sinus to allow fluid to drain from it.

Rigor Mortis

The term used to describe the stiffness of skeletal muscles that occurs shortly after an animal dies is rigor mortis, which is Latin for "stiffness of death." It would seem more sensible for the muscles to go limp after death, because all nerve stimulation ceases, but chemical reactions at the cellular level send things in another direction. When the animal dies, lack of oxygen to the cells causes normal activities and barriers within the cells to break down. One of the things that happens in skeletal muscle cells is that most of the Ca2+ spills out of the sarcoplasmic reticulum. This causes contraction of many of the muscle fibers, fueled by the last of the ATP molecules in the sarcoplasm. However, all the ATP is used up in the contraction, and no more is being made; therefore no energy source is available to relax the muscles. The result is that the muscles get stuck in the contracted position. Rigor mortis is not a permanent condition. As soon as the muscle fibers begin to decompose, the cross-bridges between the myosin and actin filaments break down and the muscles go into a relaxed state. When this happens rigor mortis has passed and the body becomes limp. Forensic experts can use the onset of rigor mortis and the subsequent muscle relaxation to help establish the time of death.

Total WBC Count and Differential Count

The total white blood cell count and differential count are used to evaluate a patient for the diagnosis or prognosis of an abnormal condition. For example, if an infection is present in the body, there will be an increased need for neutrophils to kill the invading microorganisms. The bone marrow responds to this need by releasing more neutrophils into the bloodstream that will travel to the infected tissue. The increased number of neutrophils in the blood will increase the total white blood cell count. The total white blood cell count is equal to the sum of each of the individual white blood cell counts. If one cell type increases or decreases, the total white blood cell count will increase or decrease accordingly. Sounds simple, doesn't it? Unfortunately, it's not always that simple. If one cell type increases and another cell type decreases, the net effect could be a normal total white blood cell count. That's the tricky part, so the total white blood cell count is only one of a series of tests performed to evaluate the white blood cells. To find out which white blood cells are affecting the total white blood cell count, we have to look at a stained smear of the blood. The usual method for evaluating the blood smear is to count the first 100 white blood cells observed microscopically and keep track of the number of each white blood cell type you see. This is called a differential count, commonly referred to as "the diff." Because you're counting 100 cells, the number of each cell type you see can be expressed as a percentage. For example, if you count 100 cells and find that 20 of the cells are neutrophils and 80 of the cells are lymphocytes, you would report you saw 20% neutrophils and 80% lymphocytes. There are automated hematology analyzers that will provide these numbers, but they won't pick up all cellular abnormalities. For this reason, you should always look at a stained blood smear even if you're using an automated analyzer. You don't have to complete a differential count; just look for physical abnormalities. For every species of common domestic animal, there is a value range that represents a normal white blood cell count. There is also a normal range for individual white blood cell types. For example, a dog will normally have between 6 billion and 17 billion white blood cells per liter of blood, and 60% to 70% of these cells should be neutrophils. Cattle will have between 4 billion and 12 billion white blood cells per liter and only 15% to 45% of the cells should be neutrophils. Taken together, the total white blood cell count and the differential count can provide a lot of information about an animal's state of health.

Leukemia

The word leukemia means "white blood." It is caused by an abnormal proliferation of one of the white blood cell types. In response to some unknown stimulus, the stem cells in the bone marrow start producing abnormal cells in one cell line at an increased rate. These abnormal cells show up in peripheral blood in large numbers, many times before they are mature, and cause the total white blood cell numbers to increase dramatically (leukocytosis). Leukemias are considered a form of malignancy or cancer and can be acute or chronic. They are classified by the type of cell involved (e.g., lymphocytic leukemia, monocytic leukemia, eosinophilic leukemia).

Iron Deficiency Anemia

There are trace amounts of some elements in the body that are essential for life. Iron is an example of an essential element. As a percentage of the mass of the body, iron exists in extremely small amounts. Healthy animals have only 9 to 22 mg of iron in their bodies, most of which is found in the globular protein, hemoglobin, in red blood cells. Iron is used to bind oxygen and carry it to tissues where it is needed in the mitochondria to generate adenosine triphosphate (ATP). Without iron, the level of oxygen that can be carried by the blood is reduced, leading to fatigue and exercise intolerance. Chronic blood loss reduces the level of iron stored in the body. Without adequate levels of iron, the body is not able to make hemoglobin and adequate numbers of red blood cells. In this way, ongoing blood loss results in a condition called iron deficiency anemia. A puppy or kitten with a severe flea infestation, for example, can lose 100 ml of blood a day. When the stores of iron in the body are depleted, hemoglobin can no longer be manufactured and the red blood cell count decreases. Clinical signs include pale mucous membranes, fatigue, bounding pulses, and galloping heart rhythm. Microscopic examination of the blood shows small (microcytic) pale (hypochromic) red blood cells with large central areas. The oxygen carrying capacity of blood affected by iron deficiency is greatly reduced and the animal becomes weak. If the animal is stressed and the demand for oxygen increases, such as during a physical examination at the vet's office, the puppy or kitten can die suddenly from heart failure. Iron deficiency anemia is treated by stabilizing the patient with blood transfusions, giving oral and injectable iron supplements, and eliminating the cause of the blood loss.

Renal Threshold of Glucose

There is a limit to the amount of glucose that can be reabsorbed by the proximal convoluted tubules. This limit is known as the renal threshold of glucose. If the blood glucose level gets too high, the amount of glucose filtered through the glomerulus exceeds the amount that can be reabsorbed (the renal threshold), and the excess is lost in urine. In dogs, the renal threshold for glucose is approximately 180 mg/dl (deciliter). This means that if the blood glucose level exceeds 180 mg/dl (normal blood glucose = 62-108 mg/dl) the PCT cannot reabsorb any more than 180 mg/dl back into the body. So if a dog has a blood glucose level of 500 mg/dl, only 180 mg/dl will be reabsorbed and 320 mg/dl will be lost in the urine. In cats, the renal threshold for glucose is 240 mg/dl (normal blood glucose = 60-124 mg/dl). Fortunately, the renal threshold exceeds the normal amount of glucose found in blood, so 100% of the glucose filtered through the glomerulus is reabsorbed back into the body, and no glucose is lost in the urine. However, in pathologic conditions such as uncontrolled diabetes mellitus, where blood glucose levels can be extremely high because of insufficient insulin production, the amount of glucose filtered through the glomerulus exceeds the limit that can be reabsorbed by the PCT. When this occurs, glucose appears in the urine (glycosuria). The glucose in urine pulls water out with it, which results in an abnormally high urine volume production (polyuria) due to osmosis (osmotic diuresis). The loss of water will cause a water imbalance in the body that the animal will try to correct by drinking increased amounts of water (polydipsia). Although polyuria and polydipsia (PU/PD) are nonspecific clinical signs associated with many pathologic conditions, PU/PD with an accompanying glucosuria can help pinpoint diabetes mellitus.

Tracheal Collapse

Tracheal collapse is a condition seen most commonly in toy and miniature breeds of dog. The cause is unknown, but what happens is that the usually narrow space between the ends of several of the C-shaped tracheal rings is wider than normal. When the animal inhales, the widened area of smooth muscle gets sucked down into the lumen of the trachea and partially blocks it. This can cause a dry, honking cough and difficulty breathing (dyspnea). Because the soft tissue gets sucked down into the tracheal lumen mainly during inspiration, the breathing difficulty can be described as an inspiratory dyspnea (the animal has difficulty inhaling air). The clinical signs are often most severe when the animal is breathing hard from excitement or exercise. Affected animals are commonly overweight. Therapy for tracheal collapse includes weight loss in obese animals, exercise restriction, reduction of excitement and stress, medical therapy to help control clinical signs, and surgical procedures that help hold the affected area of the trachea open.

Polychromasia and Nucleated RBCs

Under normal conditions, all but about 1% of the red blood cells in the circulation are mature. If an animal has a sudden loss or destruction of red blood cells, the bone marrow will attempt to compensate by producing more red blood cells in a shorter time. In its hurry to get red blood cells into circulation, the red bone marrow will frequently send out cells that aren't quite mature. These cells still have some metabolic activity going on in their cytoplasm, so when they are stained with a polychomatophilic hematology stain they will pick up some blue stain. There is some hemoglobin present, which will stain red. The result is lavender cytoplasm or polychromasia. Hemoglobin production begins before the cell loses its nucleus. If the bone marrow perceives a great need for oxygen-carrying hemoglobin, it may first send out all its polychromatophilic (lavender), non-nucleated cells and then also start sending nucleated red blood cells. In both cases these are immature cells that don't have their full complement of hemoglobin yet, so they can't carry a full load of oxygen. They can carry some oxygen, though, and that's better than nothing when more RBCs are needed. The presence of polychromasia and nucleated red blood cells is used as an indication that the bone marrow is responding to a need for more oxygen-carrying capacity of blood. This is a good thing.

Upper Respiratory Tract Infections

Upper respiratory tract infections are caused by disease-causing organisms, such as viruses and bacteria. They affect primarily the nasal passages and pharynx (throat) and result in coughing, sneezing, sore throat, and discharges from the eyes and nose. The common cold is a human upper respiratory tract infection. What sometimes makes upper respiratory tract infections dangerous for domestic animals is their effect on the animals' sense of smell—these infections effectively eliminate it. Think back to your last cold. You probably did not have much of a sense of smell, which rendered most foods bland and tasteless. The effect on animals that live in a smell-oriented world is even more drastic. They often stop eating and drinking completely, because they cannot smell anything. If this continues for very long, they can be in real danger from dehydration. Therefore we often have to administer fluids, either orally or by injection, to animals with upper respiratory tract infections. By keeping them properly hydrated while we provide other necessary medical and nursing care, we often can help them fight off the infection.

Urine Production Review

Urine is constantly being produced by the kidneys and sent down through the ureters into the urinary bladder for storage until it is eliminated. As plasma containing metabolic wastes passes through a nephron, the kidney converts it into urine that can be eliminated from the body. It accomplishes this through a series of processes designed to eliminate waste materials and preserve substances needed by the body to maintain homeostasis. Refer to Figure 18-5 Urine production can be broken down into six basic steps: 1. Blood enters the glomerulus via the afferent glomerular arteriole. 2. High blood pressure in the glomerular capillaries forces some plasma (minus large proteins and the blood cells) out of the capillaries and into the capsular space of Bowman's capsule. At this point, the fluid is known as the glomerular filtrate. From there, it moves into the proximal convoluted tubule and is then called tubular filtrate. 3. The balance of the plasma not forced out of the glomerular capillaries leaves the glomerulus via the efferent glomerular capillaries and enters a peritubular capillary network around the rest of the nephron. 4. While the tubular filtrate travels through the tubules of the nephron, some of its constituents, or useful substances, are reabsorbed back into the peritubular capillaries (A). 5. Waste products are secreted from the peritubular capillaries into the tubular filtrate as it travels through the tubules (B). 6. By the time the tubular filtrate reaches the collecting ducts, it has decreased in volume, has changed chemical composition many times, and is now ready to leave the kidney on its way to being eliminated. When the tubular filtrate enters the renal pelvis, it is urine, and nothing more will be done to alter its composition. (One exception here is that mucus may be added to equine urine after it reaches the renal pelvis.

Dystocia

Usually parturition comes off without a hitch. After all, animals have been giving birth for millions of years without any help. However, sometimes problems develop that interfere with the birth process, causing dystocia, or a difficult birth. The most common causes of dystocia include a fetus that is too large for the dam to pass and a fetus that is in the wrong position for delivery, which is called an abnormal presentation. Abnormal presentations may involve deviations in the position of the head, one or more legs, or the overall orientation of the fetus from the normal snout-first or rear-legs-first position. Sometimes the fetus can be pushed back far enough to allow it to be repositioned for delivery; this is called repelling the fetus. At times this is not possible, and the fetus must be removed surgically by an operation called a cesarean section, or C-section. In some cases, particularly in cattle, when the fetus is dead, it may have to be cut up (called an embryotomy) into small enough segments to be removed through the birth canal to save the life of the dam. In multiparous species, such as dogs, cats, and pigs, that normally give birth to multiple offspring, the second and third stages of parturition intermix with one another. Typically newborns and placentas are delivered alternately; that is, after a newborn is delivered, its placenta is usually expelled before the next newborn is delivered.

Vaccination Protocols 2

Vaccination protocols in young animals are established using the characteristics of both passive and active immunity. The newborn animal likely has some passive immunity from its mother (transplacentally or through colostrum) that will protect it against commonly encountered antigens. As the newborn matures the passively received antibodies are lost and protection must be activated by vaccinations and the active immune system. There is no way to know when the passive immunity disappears so initial vaccinations usually require a series of injections. For example, most puppies receive their initial vaccination somewhere around 4 to 6 weeks of age. Prior to this time we assume the puppy is protected by passive immunity. When it is about 6 weeks old the puppy must start providing its own antibodies through active immunity. To make sure we are protecting the puppy as best we can we will continue providing vaccines up to about 16 weeks of age. Most vaccines do not provide lifetime immunity so the animal's immune system must be "boosted" at regular intervals, e.g. annually, every 2 years, or every 3 years.

Venipuncture and Platelets

Venipuncture is placing a needle into a vein to draw out a blood sample or to administer medication. It makes a hole in the vessel wall. When the needle is removed, the hole will remain and connective tissue will be exposed to the inside of the vessel. This will catch the attention of platelets. The platelets will congregate at the site and form a plug that will prevent loss of blood through the hole. In a healthy animal, this plug will be in place within a couple of minutes. To ensure that the plug is formed as quickly as possible once the needle has been removed from the vein, light pressure should be applied to the venipuncture site. On small animals wrapping a piece of tape around the leg after a cotton ball has been placed on the venipuncture site can help. Don't wipe away the blood that seeps out of the venipuncture site. Every time you rub the area, you disrupt the developing platelet plug and prolong the bleeding time.

Serologic Testing

Veterinarians often need to distinguish between acute and chronic infections in animals. To help do this, serum samples from a sick animal are sent to a reference laboratory where levels of IgG and IgM are measured. The results help the veterinarian determine whether the illness affecting the animal is recent or whether it has been around for a long time. IgM antibodies are produced early in illness and are usually detectable within 1 to 2 weeks after onset of symptoms. High serum levels of IgM indicate an acute disease. IgG antibodies generally appear 2 to 6 weeks after infection and high serum levels indicate a more chronic disease.

Myelogram

We can use the spaces between the meninges in veterinary medicine when an animal is suspected of having spinal trauma due to intervertebral disc disease. For example, Dachshunds often suffer from rupture of intervertebral discs, so-called slipped discs, between the cranial lumbar vertebrae and/or caudal thoracic vertebrae. The rupture of an intervertebral disc forces the gelatinous material inside the disc through the fibrous ring of the disc dorsally, where it presses on the spinal cord. The pressure exerted by the gelatinous material compresses, or closes off, the space between the meninges on the ventral side (the underside) of the spinal cord at the point of disc rupture. To identify the existence of this material pushing up against the spinal cord, we can inject a radiopaque dye—a dye that shows up white on x-rays—into the subarachnoid space in the spinal cord, which is the space just beneath the arachnoid membrane. The subsequent radiograph will show places along the spinal cord where the dye did not flow. These areas are where the gelatinous disc material is pressing against the spinal cord and causing damage. This procedure is a form of contrast radiography called myelography.

Epidural Anesthesia

We sometimes inject anesthetic agents into the space outside the spinal cord dura mater—the outermost layer of the meninges—to produce large areas of local anesthesia. Anesthetic drugs introduced in this way block depolarization waves through spinal nerves as they emerge from the dura mater and thus remove the perception of pain from the part of the body they supply. This is called epidural anesthesia, because the anesthetic is injected into the space between the dura mater and the surrounding bone. Epidurals have the advantage of decreasing the perception of pain without having to anesthetize the brain. By not anesthetizing the brainstem and diencephalon, the body can more readily maintain its normal autonomic function during this type of anesthesia.

Preventing Wind-Up

We used to believe that potentially painful procedures we carried out on an animal under general anesthesia, such as surgery, had no long-lasting effects. After all, properly administered general anesthetics effectively block the perception of painful impulses by the conscious part of the brain. We now know that the other three nociceptive processes—transduction, transmission and modulation—are still operating full-bore in an anesthetized animal during surgery, and they can significantly affect the animal's level of pain once they wake up from the anesthetic. Most important, we now understand that the neurons of the spinal cord are bombarded with painful stimuli during surgical procedures despite the fact that the conscious mind is temporarily disconnected from the process by the general anesthetic. Because the spinal cord is capable of changing (modulating) the information it forwards on to the brain, this sensory assault during surgery can cause the pain signals going to the brain to be amplified once the animal wakes up from the general anesthesia. This can make the animal's postoperative pain level even more severe than the tissue damage caused by the surgery would seem to warrant. This exaggerated pain response is referred to as wind-up, and it can cause significant stress on a postsurgical patient. Wind-up is much easier to prevent than it is to treat. It is difficult to bring the exaggerated pain response produced by wind-up under control with drugs. On the other hand, if we can decrease the painful stimuli received by the spinal cord during surgery, we can often prevent wind-up from developing in the first place. This can be done by administering analgesic and possibly local anesthetic drugs before, and even during, surgery. Using small amounts of several drugs with different analgesic/anesthetic mechanisms is often more effective than using a large dose of a single drug. This strategy of heading off the effects of severe surgical pain before it occurs can make pain control during the postoperative period much more effective, and it can actually speed a patient's recovery from surgery.

Mucous Membranes: Keys to a Diagnosis

When animals are sick, they show signs of illness in many ways. We know that they may become depressed and lethargic. They may stop eating and drinking, may vomit, have diarrhea or bloody urine, or stop urinating entirely. Animals may show signs of illness through changes in the appearance of their mucous membranes. The easiest mucous membranes to examine are those located on the inside of the mouth and on the gums. Here, a veterinarian or veterinary technician can gain clues about the general state of the animal. For example, dehydrated animals have dry, tacky mucous membranes. Animals with wet mouths are less likely to be dehydrated. The color of mucous membranes is also very important. A yellow tinge, for example, may indicate elevation of bilirubin in the blood. This condition is known as icterus, and the yellow appearance of an animal is called jaundice. There are many causes of increased levels of bilirubin, such as liver failure and hemolytic anemia. For this reason, additional tests are needed to determine the cause of the jaundice. Blue mucous membranes occur in animals that cannot provide their tissues with adequate amounts of oxygen. These animals develop a condition called hypoxia (hypo meaning below [normal] and oxia meaning oxygen). Animals with tracheal obstruction, severe pneumonia, or circulatory collapse may all show signs of hypoxia. Bright red mucous membranes may be evident in animals that are hyperperfused, a condition in which blood flow to peripheral tissues is increased. Febrile and hypertensive animals and animals undergoing an allergic reaction may have hyperemia or bright red mucous membranes. In contrast, pale or white mucous membranes may indicate anemia, shock, or hypothermia. Finally, the clinician may gain additional clues about the state of the circulatory system by examining the gums. If pressed firmly, the pink region of a animal's gum blanches white. When released, the gum changes from white back to pink relatively quickly. The time that it takes for blood to return to the capillaries and turn the gum pink again is called the capillary refill time (CRT). Normal CRT is 1 to 2 seconds. In animals that have compromised cardiac output, low blood pressure, or severe peripheral vasoconstriction, the CRT will be prolonged. Animals with high blood pressure and those in hypercompensatory states may have shortened CRTs, lasting less than 1 second. Thus examination of the mucous membranes in an animal is very important and may lead to a greater understanding of the animal's condition.

Allergies: Itchy Business

When cats and dogs develop allergies, they do not usually develop congested sinuses and runny eyes and noses the way people do. Instead, dogs and cats develop itchy skin and ears. Like people, animals can develop an allergy to just about anything, including human dander. Imagine finding out your pet is allergic to you! Allergies to inhalant particles such as pollen, dust, and mold spores are common. This type of allergy is called atopy and can cause seasonal itchiness, as in the case of ragweed pollen, or year-round itchiness like that caused by house dust. Atopic dogs tend to rub their faces on the carpet, scratch in the axillae (armpits) with their hind feet, and lick the tops of their paws. Food allergies and allergies to ectoparasites, such as fleas, are also very common. Dogs with flea allergies tend to "corncob chew" the base of their tail and the medial sides of their hind legs. Cats rarely chew but exhibit itchiness by excessive licking, grooming, and scratching their face with a hind leg. Facial excoriations are evident in the photo on the left, and excessive grooming causes hair loss and redness on the abdomen of a cat in the photo on the right. Notice the lines of normal skin, which fall into folds when the cat is curled to lick its abdomen. To some extent the veterinarian can distinguish between the various types of allergies by the pattern of pruritus or itchiness on the body. Areas that have been scratched or licked excessively will be excoriated, raw, and hairless. In chronic cases the skin may become hyperpigmented and turn black, or areas of white fur may exhibit salivary staining by turning the hairs yellow.

Skin Cancer

With the increasing deterioration of the protective ozone layer that surrounds the earth, people are becoming more aware of the growing risk of skin cancer and the importance of protecting the skin from excessive exposure to the sun. However, we are less likely to consider skin cancer in animals, though cancer of the skin, particularly in certain species and breeds, is very common. Because cancer is the aberrant growth of cells, skin cancer can stem from any of the cell types found in the epidermis or dermis. As you have learned, many different cell types make up these layers; however, three types of particular importance in cancer are the squamous cells, melanocytes, and basal cells. Abnormal changes in the genetic programming of melanocytes, for example, can induce a deadly form of skin cancer called malignant melanoma. Malignant melanoma commonly occurs in aged gray horses and initially appears as nodules under the tail base, in the perianal area, and in the scrotum. Later, these nodules will grow, ulcerate, and spread to multiple internal locations in the horse. Although melanomas may appear on any area of the body in dogs and cats, they are most malignant in the oral cavity. Among pigs in general the disease is rare, but malignant melanoma commonly occurs in the Duroc-Jersey breed. Squamous cell carcinoma is another deadly form of skin cancer, because it spreads rapidly to local lymph nodes and is aggressively invasive locally. It tends to form circular, ulcerated lesions that seem to eat away the surrounding tissue. Squamous cell carcinoma commonly appears on the eyeball, nictitating membrane, and surrounding the eyelids of cattle and horses. It is also seen on the planum nasale, earflaps, and nose of white cats and in the vulvar regions of Merino ewes. It is one of the most common skin tumors in dogs over the age of 5. Areas of skin that receive prolonged sun exposure are most vulnerable to squamous cell carcinoma. The basal cell tumor stems from the cells found in the basal layer of the epidermis, in hair follicles, and in sebaceous glands. They do not spread to other areas of the body and therefore are considered benign; however, they do recur after removal. Basal cell tumors grow slowly and are found on the head and neck in dogs. They are thought to be one of the most common tumors found in cats but account for only 6% of the neoplasms in dogs.

Pneumothorax and Lung Collapse

Without negative intrathoracic pressure, normal breathing cannot take place. If air leaks into the pleural space (the space between the lungs and the thoracic wall), the partial vacuum is lost. The presence of free air in the thorax is called pneumothorax. It results in the lung in that area falling away from the thoracic wall because nothing is holding it in place any longer. This causes the lung to collapse, which can be a serious, life-threatening situation. The possible causes of pneumothorax and lung collapse are numerous. Generally, the air comes either from the outside, as in the case of a penetrating wound into the thorax, or from the lung itself, due to the rupture of some air-containing structure as a result of lung disease or injury. Regardless of the cause, the treatment for a collapsed lung consists of re-establishing the partial vacuum within the pleural space. This can be done in an emergency situation either by sucking the air out with a needle and syringe or by placing a chest tube that is connected to some sort of suction device into the thorax. The cause of the original air leak must be identified and corrected.

Diabetes Mellitus

Without sufficient insulin in the body, glucose does not move into body cells. It builds up in the blood, resulting in excessively high blood glucose levels (hyperglycemia), which spill over into the urine, thereby producing glycosuria, or glucose in the urine. At the same time, the body's cells are starved of energy, because they cannot absorb and use the glucose that surrounds them. Diabetes mellitus is a disease caused by a deficiency of the hormone insulin. The clinical signs of diabetes mellitus usually develop gradually. They include polyuria, polydipsia, polyphagia, weight loss, and weakness. Laboratory tests reveal hyperglycemia (too high a level of glucose in the blood) and glycosuria. The condition can be fatal if left untreated. Diabetes mellitus is not presently curable, but it often can be controlled effectively through appropriate treatment. This approach usually involves careful management of the animal's diet and amount of exercise, administration of insulin injections once or twice a day, and frequent monitoring of the animal's urine and blood glucose levels. The dose of insulin must be carefully controlled, because an overdose can result in hypoglycemia (too low a level of glucose in the blood), which can lead to weakness and collapse.