Psych 474: Ch.2 The Systems of the Body

Disorders Associated with the Respiratory System

.

Dealing with Respiratory Disorders

A number of respiratory disorders can be addressed by health psychologists. For example, smoking is implicated in both pulmonary emphysema and lung cancer. Dangerous substances in the workplace and air pollution are also factors that contribute to the incidence of respiratory problems. As we will see in Chapters 3-5, health psychologists have conducted research on many of these problems and discussed the clinical issues they raise. Some respiratory disorders are chronic conditions. Consequently, issues of long-term physical, vocational, social, and psychological rehabilitation become important.

Peptic Ulcer

A peptic ulcer is an open sore in the lining of the stomach or the duodenum. It results from the hypersecretion of hydrochloric acid and occurs when pepsin, a protein-digesting enzyme secreted in the stomach, digests a portion of the stomach wall or duodenum. A bacterium called H. pylori is believed to contribute to the development of many ulcers. Once thought to be primarily psychological in origin, ulcers are now believed to be aggravated by stress, but not caused by it.

The Structure & Function of the Respiratory System

Air is inhaled through the nose and mouth and then passes through the pharynx and larynx to the trachea. The trachea, a muscular tube extending downward from the larynx, divides at its lower end into two branches called the primary bronchi. Each bronchus enters a lung, where it then subdivides into secondary bronchi, still-smaller bronchioles, and, finally, microscopic alveolar ducts, which contain many tiny clustered sacs called alveoli. The alveoli and the capillaries are responsible for the exchange of oxygen and carbon dioxide.

Multiple Sclerosis (MS)

Approximately 2.3 million people worldwide have multiple sclerosis. This degenerative disease can cause paralysis and, occasionally, blindness, deafness, and mental deterioration. Early symptoms include numbness, double vision, dragging of the feet, loss of bladder or bowel control, speech difficulties, and extreme fatigue. Symptoms may appear and disappear over a period of years; after that, deterioration is continuous. The effects of multiple sclerosis result from the disintegration of myelin, a fatty membrane that surrounds nerve fibers and facilitates the conduction of nerve impulses. Multiple sclerosis is an autoimmune disorder, so called because the immune system fails to recognize its own tissue and attacks the myelin sheath surrounding nerve fibers.

Disorders of the Nervous System

Approximately 25 million Americans have some disorder of the nervous system. The most common forms of neurological dysfunction are epilepsy and Parkinson's disease. Cerebral palsy, multiple sclerosis, and Huntington's disease also affect substantial numbers of people.

Parkinson's Disease

Patients with Parkinson's disease have progressive degeneration of the basal ganglia, a group of nuclei in the brain that control smooth motor coordination. The result of this deterioration is tremors, rigidity, and slowness of movement. As many as one million Americans have Parkinson's disease, which primarily strikes people age 50 and older; men are more likely than women to develop the disease. Although the cause of Parkinson's is not fully known, depletion of the neurotransmitter dopamine may be involved. Parkinson's patients may be treated with medication, but large doses, which can cause undesirable side effects, are often required for control of the symptoms.

The Heart

The heart functions as a pump, and its pumping action causes the blood to circulate throughout the body. The left side of the heart, consisting of the left atrium and left ventricle, takes in oxygenated blood from the lungs and pumps it out into the aorta (the major artery leaving the heart), from which the blood passes into the smaller vessels (the arteries, arterioles, and capillaries) to reach the cell tissues. The blood exchanges its oxygen and nutrients for the waste materials of the cells and is then returned to the right side of the heart (right atrium and right ventricle), which pumps it back to the lungs via the pulmonary artery. Once oxygenated, the blood returns to the left side of the heart through the pulmonary veins.

the cardiac cycle.

The heart performs these functions through regular rhythmic phases of contraction and relaxation known as the cardiac cycle. There are two phases in the cardiac cycle: systole and diastole. During systole, blood is pumped out of the heart, and blood pressure in the blood vessels increases. As the muscle relaxes during diastole, blood pressure drops, and blood is taken into the heart.

Increase in the prevalence of allergic disorders

The numbers are increasing, especially in industrialized countries and in urban as opposed to rural areas. Asthma rates are especially high in low income areas, and psychosocial stressors may play a role in aggravating an underlying vulnerability. However, the reasons for these dramatic changes are not yet fully known. Children who have a lot of infectious disorders during childhood are less likely to develop allergies, suggesting that exposure to infectious agents plays a protective role. Thus, paradoxically, the improved hygiene of industrialized countries may actually be contributing to the high rates of allergic disorders currently seen.

Tuberculosis and Pleurisy

Tuberculosis (TB) is an infectious disease caused by bacteria that invade lung tissue. When the invading bacilli are surrounded by macrophages (white blood cells of a particular type), they form a clump called a tubercle. Eventually, through a process called caseation, the center of the tubercle turns into a cheesy mass, which can produce cavities in the lung. Such cavities, in turn, can give rise to permanent scar tissue, causing chronic difficulties in oxygen and carbon dioxide exchange between the blood and the alveoli. Once the leading cause of death in the United States, it has been in decline for several decades. However, worldwide, it remains common and deadly, affecting one-third of the world's population (Centers for Disease Control, 2015). Pleurisy is an inflammation of the pleura, the membrane that surrounds the organs in the thoracic cavity. The inflammation, which produces a sticky fluid, is usually a consequence of pneumonia or tuberculosis and can be extremely painful.

Fertilization and Gestation .

When sexual intercourse takes place and ejaculation occurs, sperm are released into the vagina. These sperm, which have a high degree of motility, proceed upward through the uterus into the fallopian tubes, where one sperm may fertilize an ovum. The fertilized ovum then travels down the fallopian tube into the uterine cavity, where it embeds itself in the uterine wall and develops over the next 9 months into a human being.

The Nervous System

a complex network of interconnected nerve fibers. made up of the central nervous system, which consists of the brain and the spinal cord, and the peripheral nervous system, which consists of the rest of the nerves in the body, including those that connect to the brain and spinal cord. Sensory nerve fibers provide input to the brain and spinal cord by carrying signals from sensory receptors; motor nerve fibers provide output from the brain or spinal cord to muscles and other organs, resulting in voluntary and involuntary movement.

Ischemia

a condition characterized by lack of blood flow and oxygen to the heart muscle. As many as 3 to 4 million Americans have silent ischemic episodes without knowing it, and they may consequently have a heart attack with no prior warning

Chronic traumatic encephalopathy (CTE)

a degenerative brain disorder that strikes people who have had repeated or serious head injuries. Former boxers and football players, for example, have high rates of CTE. In CTE, an abnormal form of a protein accumulates and eventually destroys cells in the brain, including the frontal and temporal lobes, which are critical for decision making, impulse control, and judgment.

Kidney Failure

a severe disorder because the inability to produce an adequate amount of urine will cause the waste products of metabolism, as well as surplus inorganic salts and water, to be retained in the body. An artificial kidney, a kidney transplant, or kidney dialysis may be required in order to rid the body of its wastes. Although these technologies can cleanse the blood to remove the excess salts, water, and metabolites, they are highly stressful medical procedures. Kidney transplants carry many health risks, and kidney dialysis can be extremely uncomfortable for patients. Consequently, health psychologists have been involved in addressing these problems.

Respiratory movements

are controlled by a respiratory center in the medulla. The functions of this center depend partly on the chemical composition of the blood. For example, if the blood's carbon dioxide level rises too high, the respiratory center will be stimulated and respiration will be increased. If the carbon dioxide level falls too low, the respiratory center will slow down until the carbon dioxide level is back to normal.

Red Blood Cells

are important mainly because they contain hemoglobin, which is needed to carry oxygen and carbon dioxide throughout the body. Anemia, which involves below-normal numbers of red blood cells, can interfere with this transport function.

The Parasympathetic Nervous System

controls the activities of organs under normal circumstances and acts antagonistically to the sympathetic nervous system. When an emergency has passed, the parasympathetic nervous system helps to restore the body to a normal state. Parasympathetic functioning is a counterregulatory system that helps restore homeostasis following sympathetic arousal. The heart rate decreases, the heart's capillaries constrict, blood vessels dilate, respiration rate decreases, and the metabolic system resumes its activities. .

The Cerebellum

coordinates voluntary muscle movement, the maintenance of balance and equilibrium, and the maintenance of muscle tone and posture. Damage to this area can produce loss of muscle tone, tremors, and disturbances in posture or gait.

The Hypothalamus

example, embarrassment can lead to blushing via the hypothalamus through the vasomotor center in the medulla to the blood vessels. Together with the pituitary gland, the hypothalamus helps regulate the endocrine system, which releases hormones that affect functioning in target organs throughout the body.

The Adrenal Glands

glands that help the body recover from stress and respond to emergencies. The adrenal glands are critically involved in physiological and neuroendocrine reactions to stress. Catecholamines, secreted in conjunction with sympathetic arousal, and corticosteroids are implicated in biological responses to stress.

Each lobe

has a role in associative memory but also each lobe is generally associated with particular functions.

The Hindbrain and the Midbrain

has three main parts: the medulla, the pons, and the cerebellum.

The Forebrain

includes the thalamus and the hypothalamus.

Cancer in the Reproductive System

including testicular cancer in men and gynecologic cancers in women. Every 6 minutes, a woman in the United States is diagnosed with a gynecologic cancer, including cancer of the cervix, uterus, and ovaries (American Cancer Society, 2012a). Endometrial cancer is the most common female pelvic malignancy, and ovarian cancer is the most lethal.

The inspiration of air

is an active process, brought about by the contraction of muscles. Inspiration causes the lungs to expand inside the thorax (the chest wall). Expiration, in contrast, is a passive function, brought about by the relaxation of the lungs, which reduces the volume of the lungs within the thorax. The lungs fill most of the space within the thoracic cavity and are very elastic, depending on the thoracic walls for support. If air gets into the space between the thoracic wall and the lungs, one or both lungs will collapse.

The Thalamus

is involved in the recognition of sensory stimuli and the relay of sensory impulses to the cerebral cortex.

The medulla

is responsible for the regulation of heart rate, blood pressure, and respiration. Sensory information about the levels of carbon dioxide and oxygen in the body also comes to the medulla, which, if necessary, sends motor impulses to respiratory muscles to alter the rate of breathing.

Immunity

is the body's resistance to invading organisms. It may develop either naturally or artificially. Some natural immunity is passed from the mother to the child at birth and through breast-feeding, although this type of immunity is only temporary. Natural immunity is also acquired through disease. For example, if you have measles once, you are unlikely to develop it a second time; you will have built up an immunity to it. Artificial immunity is acquired through vaccinations and inoculations. For example, most children and adolescents receive shots for a variety of diseases— among them, diphtheria, whooping cough, smallpox, poliomyelitis, and hepatitis—so that they will not contract these diseases, should they be exposed.

The pons

serves as a link between the hindbrain and the midbrain and also helps control respiration.

Epilepsy

A disease of the central nervous system affecting 1 in 26 people in the United States (Epilepsy Foundation, 2014), epilepsy is often idiopathic, which means that no specific cause for the symptoms can be identified. Symptomatic epilepsy may be traced to harm during birth, severe injury to the head, infectious disease such as meningitis or encephalitis, or metabolic or nutritional disorders. Risk for epilepsy may also be inherited. Epilepsy is marked by seizures, which range from barely noticeable to violent convulsions accompanied by irregular breathing and loss of consciousness. Epilepsy cannot be cured, but it can often be controlled through medication and behavioral interventions designed to manage stress

Huntington's Disease

A hereditary disorder of the central nervous system, Huntington's disease is characterized by chronic physical and mental deterioration. Symptoms include involuntary muscle spasms, loss of motor abilities, personality changes, and other signs of mental disintegration. The disease affects about 30,000 people directly, and 200,000 more are at risk in the United States. The gene for Huntington's has been isolated, and a test is now available that indicates not only if one is a carrier of the gene but also at what age (roughly) one will succumb to the disease. As will be seen later in this chapter, genetic counseling with this group of at-risk people is important.

The Blood

An adult's body contains approximately 5 liters of blood, which consists of plasma and cells. Plasma, the fluid portion of blood, accounts for approximately 55 percent of the blood volume. The remaining 45 percent of blood volume is made up of cells. The blood cells are suspended in the plasma, which contains plasma proteins and plasma electrolytes (salts) plus the substances that are being transported by the blood (oxygen and nutrients or carbon dioxide and waste materials). The blood also helps to regulate skin temperature. Blood cells are manufactured in the bone marrow in the hollow cavities of bones. Bone marrow contains five types of blood-forming cells: myeloblasts and monoblasts, both of which produce particular white blood cells; lymphoblasts, which produce lymphocytes; erythroblasts, which produce red blood cells; and megakaryocytes, which produce platelets. Each of these types of blood cells has an important function.

Appendicitis

Appendicitis is a common condition that occurs when wastes and bacteria accumulate in the appendix. If the small opening of the appendix becomes obstructed, bacteria can easily proliferate. Soon this condition gives rise to pain, increased peristalsis, and nausea. If the appendix ruptures and the bacteria are released into the abdominal cavity or peritoneum, they can cause further infection (peritonitis) or even death.

Fertility Problems

Approximately 10 percent of U.S. couples experience fertility problems, defined as the inability to conceive a pregnancy after 1 year of regular sexual intercourse without contraception. Although physicians once believed that infertility has emotional origins, researchers now believe that distress may complicate but does not cause infertility. Fortunately, over the past few decades, the technology for treating infertility has improved. A variety of drug treatments have been developed, as have more invasive technologies. In vitro fertilization (IVF) is the most widely used method of assistive reproductive technology, and the success rate for IVF can be as high as 40% per cycle

The Course of Infection

Assuming that the invading organism does gain a foothold, the natural history of infection follows a specific course. First, there is an incubation period between the time the infection is contracted and the time the symptoms appear. Next, there is a period of nonspecific symptoms, such as headaches and general discomfort, which precedes the onset of the disorder. During this time, the microbes are actively colonizing and producing toxins. The next stage is the acute phase, when the illness and its symptoms are at their height. Unless the infection proves fatal, a period of decline follows the acute phase. During this period, the organisms are expelled from the mouth and nose in saliva and respiratory secretions, as well as through the digestive tract and the genitourinary system in feces and urine. Infections may be localized, focal, or systemic. Localized infections remain at their original site and do not spread throughout the body. Although a local infection is confined to a particular area, it sends toxins to other parts of the body, causing other disruptions. Systemic infections affect a number of areas or body systems. The primary infection initiated by the microbe may also lead to secondary infections. These occur because the body's resistance is lowered from fighting the primary infection, leaving it susceptible to other invaders. In many cases, secondary infections, such as pneumonia, pose a greater risk than the primary one.

Asthma

Asthma is a severe allergic reaction typically to a foreign substance, including dust, dog or cat dander, pollens, or fungi. An asthma attack can also be touched off by emotional stress or exercise. These attacks may be so serious that they produce bronchial spasms and hyperventilation. During an asthma attack, the muscles surrounding air tubes constrict, inflammation and swelling of the lining of the air tubes occur, and increased mucus is produced, clogging the air tubes. The mucus secretion, in turn, may then obstruct the bronchioles, reducing the supply of oxygen and increasing the amount of carbon dioxide

chronic obstructive pulmonary disease (COPD)

Chronic obstructive pulmonary disease (COPD), including chronic bronchitis and emphysema, is the fourth-leading killer of people in the United States. Some 12 million Americans have COPD (COPD International, 2015). Although COPD is not curable, it is preventable. Its chief cause is smoking, which accounts for over 80 percent of all cases of COPD.

Clotting Disorders

Clots (or thromboses) can sometimes develop in the blood vessels. This is most likely to occur if arterial or venous walls have been damaged or roughened because of the buildup of cholesterol. Platelets then adhere to the roughened area, leading to the formation of a clot. A clot can have especially serious consequences if it occurs in the blood vessels leading to the heart (coronary thrombosis) or brain (cerebral thrombosis), because it will block the vital flow of blood to these organs. When a clot occurs in a vein, it may become detached and form an embolus, which can become lodged in the blood vessels to the the lungs, causing pulmonary obstruction. Death is a common consequence of these conditions.

Cerebral Palsy

Currently, more than 764,000 people in the United States have or experience symptoms of cerebral palsy. Cerebral palsy is a chronic, nonprogressive disorder marked by lack of muscle control. It stems from brain damage caused by an interruption in the brain's oxygen supply, usually during childbirth. In older children, a severe accident or physical abuse can produce the condition. Apart from being unable to control motor functions, those who have the disorder may (but need not) also have seizures, spasms, mental retardation, difficulties with sensation and perception, and problems with sight, hearing, and/or speech.

Dementia

Dementia (meaning "deprived of mind") is a serious loss of cognitive ability beyond what might be expected from normal aging. A history of brain injuries or a genetically-based propensity may be involved in long-term decline. Although dementia is most common among older adults, it may occur at any stage of adulthood. Memory, attention, language, and problem solving are affected early in the disorder and often lead to diagnosis. The most common form of dementia is Alzheimer's, accounting for 60-70% of the cases. In most people, symptoms appear in their mid-60s, and the disease progresses irreversibly, due to plaques and tangles in the progressively shrinking brain. In addition to the early signs of cognitive decline, especially difficulty with short term memory, social functioning, and use of language, are disrupted as the disease progresses. About 48 million people worldwide have Alzheimer's.

Disorders Involving the Endocrine System

Diabetes is a chronic endocrine disorder in which the body is not able to manufacture or properly use insulin. It is the fourth most common chronic illness in this country and one of the leading causes of death. Diabetes consists of two primary forms. Type I diabetes is a severe disorder that typically arises in late childhood or early adolescence. At least partly genetic in origin, Type I diabetes is an autoimmune disorder, possibly precipitated by an earlier viral infection. The immune system falsely identifies cells in the islets of Langerhans in the pancreas as invaders and destroys those cells, compromising or eliminating their ability to produce insulin. Type II diabetes, which typically occurs after age 40, is the more common form. In Type II diabetes, insulin may be produced by the body, but there may not be enough of it, or the body may not be sensitive to it. It is heavily a disease of lifestyle, and risk factors include obesity and stress, among other factors. Diabetic patients have high rates of coronary heart disease, and diabetes is the leading cause of blindness among adults. It accounts for almost 50 percent of all the patients who require renal dialysis for kidney failure. Diabetes can also produce nervous system damage, leading to pain and loss of sensation. In severe cases, amputation of the extremities, such as toes and feet, may be required. As a consequence of these complications, people with diabetes have a considerably shortened life expectancy.

THE IMMUNE SYSTEM

Disease is caused by a variety of factors. In this section, we address the transmission of disease by infection, that is, the invasion of microbes and their growth in the body. The microbes that cause infection are transmitted to people in several ways: ∙ Direct transmission involves bodily contact, such as handshaking, kissing, and sexual intercourse. For example, genital herpes is typically contracted by direct transmission. ∙ Indirect transmission (or environmental transmission) occurs when microbes are passed to an individual via airborne particles, dust, water, soil, or food. Influenza is an example of an environmentally transmitted disease. ∙ Biological transmission occurs when a transmitting agent, such as a mosquito, picks up microbes, changes them into a form conducive to growth in the human body, and passes them on to the human. Yellow fever, for example, is transmitted by this method. ∙ Mechanical transmission is the passage of a microbe to an individual by means of a carrier that is not directly involved in the disease process. Dirty hands, bad water, rats, mice, and flies can be implicated in mechanical transmission. Box 2.2 tells about two people who were carriers of deadly diseases.

the rate at which the heart contracts and relaxes.

During exercise, emotional excitement, or stress, for example, the heart speeds up, and the cardiac cycle is completed in a shorter time. A chronically or excessively rapid heart rate can decrease the heart's strength, which may reduce the volume of blood that is pumped.

The Functioning of the Digestive System

Food is first lubricated by saliva in the mouth, where it forms a soft, rounded lump called a bolus. It passes through the esophagus by means of peristalsis, a unidirectional muscular movement toward the stomach. The stomach produces various gastric secretions, including pepsin and hydrochloric acid, to further the digestive process. The sight or even the thought of food starts the flow of gastric juices.

THE DIGESTIVE SYSTEM AND THE METABOLISM OF FOOD

Food, essential for survival, is converted through the process of metabolism into heat and energy, and it supplies nutrients for growth and the repair of tissues. But before food can be used by cells, it must be changed into a form suitable for absorption into the blood. This conversion process is called digestion.

Gastroenteritis, Diarrhea, and Dysentery

Gastroenteritis is an inflammation of the lining of the stomach and small intestine. It may be caused by excessive amounts of food or drink, contaminated food or water, or food poisoning. Symptoms appear approximately 2-4 hours after the ingestion of food and include vomiting, diarrhea, abdominal cramps, and nausea. Diarrhea, characterized by watery and frequent bowel movements, occurs when the lining of the small and large intestines cannot properly absorb water or digested food. Chronic diarrhea may result in serious disturbances of fluid and electrolyte (sodium, potassium, magnesium, calcium) balance. Dysentery is similar to diarrhea except that mucus, pus, and blood are also excreted. It may be caused by a protozoan that attacks the large intestine (amoebic dysentery) or by a bacterial organism. Although these conditions are only rarely life threatening in industrialized countries, in developing countries, they are among the most common causes of death.

Gastroesophageal reflux disease

Gastroesophageal reflux disease (GERD), also known as acid reflux disease, results from an abnormal reflux in the esophagus. This is commonly due to changes in the barrier between the esophagus and the stomach. As much as 60 percent of the U.S. adult population experiences acid reflux at least occasionally

Genetics and Susceptibility to Disorders

Genetic studies have provided valuable information about the inheritance of susceptibility to disease. For example, scientists have bred strains of rats, mice, and other laboratory animals that are sensitive or insensitive to the development of particular diseases and then used these strains to study illness onset and the course of illness. For example, a strain of rats that is susceptible to cancer may shed light on the development of this disease and what other factors contribute to its occurrence. The initial susceptibility of the rats ensures that many of them will develop malignancies when implanted with carcinogenic (cancer-causing) materials. In humans, several types of research help demonstrate whether a characteristic is genetically acquired. Studies of families, for example, can reveal whether members of the same family are more likely to develop a disorder, such as heart disease, than are unrelated individuals in a similar environment. If a factor is genetically determined, family members will show it more frequently than will unrelated individuals. Twin research is another method for examining the genetic basis of a characteristic. If a characteristic is genetically transmitted, identical twins share it more commonly than do fraternal twins or other brothers and sisters. This is because identical twins share the same genetic makeup, whereas other brothers and sisters have only partially overlapping genetic makeup. their adoptive parents, but they may manifest environmentally transmitted characteristics. Consider, for example, obesity, which is a risk factor for a number of disorders, including coronary artery disease and diabetes. If twins reared apart show highly similar body weights, then we would suspect that body weight has a genetic component. If, on the other hand, weight within a family is highly related, and adopted children show the same weight as their parents and any natural offspring, then we would look to the family diet as a potential cause of obesity. For many attributes, including obesity, both environmental and genetic factors are involved. Research like this has increasingly uncovered the genetic contribution to many health disorders and behavioral factors that may pose risks to health. Such diseases as asthma, Alzheimer's disease, cystic fibrosis, muscular dystrophy, Tay-Sachs disease, and Huntington's disease have a genetic basis. There is also a genetic basis for coronary heart disease and for some forms of cancer, including some breast and colon cancers. This genetic basis does not preclude the important role of the environment, however. Genetics will continue to be of interest as the contribution of genes to health continues to be uncovered. For example, genetic contributions to obesity and alcoholism have emerged in recent years. Moreover, the contributions of genetics studies to health psychology are broadening. Even some personality characteristics, such as optimism, which is believed to have protective health effects, have genetic underpinnings

Infection

Once a microbe has reached the body, it penetrates into bodily tissue via any of several routes, including the skin, the throat and respiratory tract, the digestive tract, or the genitourinary system. Whether the invading microbes gain a foothold in the body and produce infection depends on three factors: the number of organisms, the virulence of the organisms, and the body's defensive capacities. The virulence of an organism is determined by its aggressiveness (i.e., its ability to resist the body's defenses) and by its toxigenicity (i.e., its ability to produce poisons, which invade other parts of the body).

Genetics and Health Psychology

Health psychologists have important roles to play with respect to genetic contributions to health disorders. One question concerns whether people need to be alerted to genetic risks. Many people think that genetic risks are immutable and that any efforts they might undertake to affect their positive represents an important role for health psychologists. For example, belief in a genetic cause can lead people to take medical actions that may be medically unwarranted . In addition, people who have a family history of genetic disorders, those who have already given birth to a child with a genetic disorder, or those who have recurrent reproductive problems, such as multiple miscarriages, often seek such counseling. In some cases, technological advances have made it possible to treat some of these problems before birth through drugs or surgery. However, if the condition cannot be corrected, the parents often must make the difficult decision of whether to abort the pregnancy. Children, adolescents, and young adults sometimes learn of a genetic risk to their health, as research uncovers such causes. Breast cancer, for example, runs in families, and among young women whose mothers, aunts, or sisters have developed breast cancer, vulnerability is higher. Families that share genetic risks may need special attention through family counseling . Some of the genes that contribute to the development of breast cancer have been identified, and tests are now available to determine whether a genetic susceptibility is present. Although this type of cancer accounts for only 5 percent of breast cancer, women who carry these genetic susceptibilities are more likely to develop the disease at an earlier age; thus, these women are at high risk and need careful monitoring and assistance in making

Hepatitis .

Hepatitis means "inflammation of the liver," and the disease produces swelling, tenderness, and sometimes permanent damage. When the liver is inflamed, bilirubin, a product of the breakdown of hemoglobin, cannot easily pass into the bile ducts. Consequently, it remains in the blood, causing a yellowing of the skin known as jaundice. Other common symptoms are fatigue, fever, muscle or joint aches, nausea, vomiting, loss of appetite, abdominal pain, and diarrhea. There are several types of hepatitis, which differ in severity and mode of transmission. Hepatitis A, caused by viruses, is typically transmitted through food and water. It is often spread by poorly cooked seafood or through unsanitary preparation or storage of food. Hepatitis B is a more serious form, with 2 billion people infected worldwide and 1 million deaths annually. Also known as serum hepatitis, it is caused by a virus and is transmitted by the transfusion of infected blood, by improperly sterilized needles, through sexual contact, and through mother-to-infant contact. It is a particular risk among intravenous drug users. Its symptoms are similar to those of hepatitis A but are far more serious. Hepatitis C, also spread via blood and needles, is most commonly caused by blood transfusions; 130-150 million people worldwide have the disorder, which accounts for half a million deaths annually. Hepatitis D is found mainly in intravenous drug users who are also carriers of hepatitis B, necessary for the hepatitis D virus to spread. Finally, hepatitis E resembles hepatitis A but is caused by a different virus.

Natural and Specific Immunity

How does immunity work? The body has a number of responses to invading organisms, some nonspecific and others specific. Nonspecific immune mechanisms are a general set of responses to any kind of infection or disorder; specific immune mechanisms, which are always acquired after birth, fight particular microorganisms and their toxins. Natural immunity is involved in defense against pathogens. The cells involved in natural immunity provide defense not against a particular pathogen, but rather against many pathogens. The largest group of cells involved in natural immunity is granulocytes, which include neutrophils and macrophages; both are phagocytic cells that engulf target pathogens. Neutrophils and macrophages congregate at the site of an injury or infection and release toxic substances. Macrophages release cytokines that lead to inflammation and fever, among other side effects, and promote wound healing. Natural killer cells are also involved in natural immunity; they recognize "nonself" material (such as viral infections or cancer cells) and lyse (break up and disintegrate) those cells by releasing toxic substances. Natural killer cells are believed to be important in signaling potential malignancies and in limiting early phases of viral infections. Natural immunity occurs through four main ways: anatomical barriers, phagocytosis, antimicrobial substances, and inflammatory responses. Anatomical barriers prevent the passage of microbes from one section of the body to another. For example, the skin functions as an effective anatomical barrier to many infections, and the mucous membranes lining the nose and mouth also provide protection.

Paraplegia and Quadriplegia

Paraplegia is paralysis of the lower extremities of the body; it results from an injury to the lower portion of the spinal cord. Quadriplegia is paralysis of all four extremities and the trunk of the body; it occurs when the upper portion of the spinal cord is severed. People who have these conditions usually lose bladder and bowel control and the muscles below the cut area may lose their tone, becoming weak and flaccid.

Pituitary Gland

Located at the base of the brain, the pituitary has two lobes. The posterior pituitary lobe produces oxytocin, which controls contractions during labor and lactation and is also involved in social affiliation, and vasopressin, or antidiuretic hormone (ADH), which controls the water-absorbing ability of the kidneys, among other functions. The anterior pituitary lobe of the pituitary gland secretes hormones responsible for growth: somatotropic hormone (STH), which regulates bone, muscle, and other organ development; gonadotropic hormones, which control the growth, development, and secretions of the gonads (testes and ovaries); thyrotropic hormone (TSH), which controls the growth, development, and secretion of the thyroid gland; and adrenocorticotropic hormone (ACTH), which controls the growth and secretions of the cortex region of the adrenal glands.

Lung Cancer

Lung cancer is a disease of uncontrolled cell growth in tissues of the lung. The affected cells begin to divide in a rapid and unrestricted manner, producing a tumor. Malignant cells grow faster than healthy cells. This growth may lead to metastasis, which is the invasion of adjacent tissue and infiltration beyond the lungs. The most common symptoms are shortness of breath, coughing (including coughing up blood), and weight loss. Smoking is one of the primary causes.

Polio

Poliomyelitis is a highly infectious viral disease that affects mostly young children. It attacks the spinal nerves and destroys the cell bodies of motor neurons so that motor impulses cannot be carried from the spinal cord outward to the peripheral nerves or muscles. Depending on the degree of damage that is done, the person may be left with difficulties in walking and moving properly, ranging from shrunken and ineffective limbs to full paralysis. Polio cases have decreased substantially worldwide, although polio is still a major health issue in Pakistan and Afghanistan.

hypothalamus and the pituitary gland.

Regulates the Endocrine System

The Respiratory System

Respiration, or breathing, has three main functions: to take in oxygen, to excrete carbon dioxide, and to regulate the composition of the blood. The body needs oxygen to metabolize food. During the process of metabolism, oxygen combines with carbon atoms in food, producing carbon dioxide (CO2). The respiratory system brings in oxygen through inspiration; it eliminates carbon dioxide through expiration.

Disorders of the Cardiovascular System

Some of these are due to congenital defects defects—that is, defects present at birth—and others, to infection. By far, however, the major threats to the cardiovascular system are due to lifestyle factors, including stress, poor diet, lack of exercise, and smoking.

The Reproductive System

The development of the reproductive system is controlled by the pituitary gland. The anterior pituitary lobe produces the gonadotropic hormones, which control development of the ovaries in females and the testes in males.

The Ovaries and the Testes

The female has two ovaries located in the pelvis. Each month, one of the ovaries releases an ovum (egg), which is discharged at ovulation into the fallopian tubes. If the ovum is not fertilized (by sperm), it remains in the uterine cavity for about 14 days and is then flushed out of the system with the uterine endometrium and its blood vessels (during menstruation). The ovaries also produce the hormones estrogen and progesterone. Estrogen leads to the development of secondary sex characteristics in females, including breasts and the distribution of both body fat and body hair. Progesterone, which is produced during the second half of the menstrual cycle to prepare the body for pregnancy, declines if pregnancy fails to occur. In males, testosterone is produced by the interstitial cells of the testes under the control of the anterior pituitary lobe. It brings about the production of sperm and the development of secondary sex characteristics, including growth of the beard, deepening of the voice, distribution of body hair, and both skeletal and muscular growth.

Genetics & Health

The fetus starts life as a single cell, which contains the inherited information from both parents that will determine its characteristics. The genetic code regulates such factors as eye and hair color, as well as behavioral factors. Genetic material for inheritance lies in the nucleus of the cell in the form of 46 chromosomes, 23 from the mother and 23 from the father. Two of these 46 are sex chromosomes, which are an X from the mother and either an X or a Y from the father. If the father provides an X chromosome, a female child will result; if he provides a Y chromosome, a male child will result.

Disorders of the Reproductive System

The reproductive system is vulnerable to a number of diseases and disorders. Among the most common and problematic are sexually transmitted diseases (STDs), which occur through sexual intercourse or other forms of sexually intimate activity. STDs include herpes, gonorrhea, syphilis, genital warts, chlamydia, and, most seriously, AIDS. For women, a risk from several STDs is chronic pelvic inflammatory disease (PID), which may produce severe abdominal pain and infections that may compromise fertility. Other gynecologic disorders to which women are vulnerable include vaginitis, endometriosis (in which pieces of the endometrial lining of the uterus move into the fallopian tubes or abdominal cavity, grow, and spread to other sites), cysts, and fibroids (nonmalignant growths in the uterus that may nonetheless interfere with reproduction). Women are vulnerable to disorders of the menstrual cycle, including amenorrhea, which is the absence of menses, and oligomenorrhea, which is infrequent menstruation.

Coughing

The respiratory system is also responsible for coughing. Dust and other foreign materials are inhaled with every breath. Some of these substances are trapped in the mucus of the nose and the air passages and are then conducted back toward the throat, where they are swallowed. When a large amount of mucus collects in the large airways, it is removed by coughing (a forced expiratory effort).

Bacterial Infections

The respiratory system is also vulnerable to bacterial disorders, including strep throat, whooping cough, and diphtheria. Usually, these disorders do not cause permanent damage to the upper respiratory tract. The main danger is the possibility of secondary infection, which results from lowered resistance. However, these bacterial infections can cause permanent damage to other tissues, including heart tissue.

Viral Infections

The respiratory system is vulnerable to infections, especially the common cold, a viral infection of the upper and sometimes the lower respiratory tract. The infection that results causes discomfort, congestion, and excessive secretion of mucus. The incubation period for a cold—that is, the time between exposure to the virus and onset of symptoms—is 12-72 hours, and the typical duration is a few days. Secondary bacterial infections may complicate the illness. These occur because the primary viral infection causes inflammation of the mucous membranes, reducing their ability to prevent secondary infection. Bronchitis is an inflammation of the mucosal membrane inside the bronchi of the lungs. Large amounts of mucus are produced in bronchitis, leading to persistent coughing. A serious viral infection of the respiratory system is influenza, which can occur in epidemic form. Flu viruses attack the lining of the respiratory tract, killing healthy cells. Fever and inflammation of the respiratory tract may result. A common complication is a secondary bacterial infection, such as pneumonia.

Pneumonia

There are two main types of pneumonia. Lobar pneumonia is a primary infection of the entire lobe of a lung. The alveoli become inflamed, and the normal oxygen-carbon dioxide exchange between the blood and alveoli can be disrupted. Spread of infection to other organs is also likely. Bronchial pneumonia, which is confined to the bronchi, is typically a secondary infection that may occur as a complication of other disorders, such as a severe cold or flu. It is not as serious as lobar pneumonia.

Most metabolic products

are water soluble and can be easily transported in the blood, but some substances, such as lipids, are not soluble in water and so must be transported in the blood plasma. Lipids include fats, cholesterol, and lecithin. An excess of lipids in the blood is called hyperlipidemia, a condition common in diabetes, some kidney diseases, hyperthyroidism, and alcoholism. It is also a causal factor in the development of heart disease.

the heart is controlled by valves

at the inlet and outlet of each ventricle. These heart valves ensure that blood flows in one direction only. The sounds that one hears when listening to the heart are the sounds of these valves closing. These heart sounds make it possible to time the cardiac cycle to determine how rapidly or slowly blood is being pumped into and out of the heart.

Atherosclerosis

caused by deposits of cholesterol and other substances on the arterial walls, which form plaques that narrow the arteries. These plaques reduce the flow of blood through the arteries and interfere with the passage of nutrients from the capillaries into the cells—a process that can lead to tissue damage. Damaged arterial walls are also potential sites for the formation of blood clots, which can obstruct a vessel and cut off the flow of blood.

THE ENDOCRINE SYSTEM

complements the nervous system in controlling bodily activities. The endocrine system is made up of a number of ductless glands that secrete hormones into the blood, stimulating changes in target organs. The endocrine and nervous systems depend on each other, stimulating and inhibiting each other's activities. The nervous system is chiefly responsible for fast-acting, short-duration responses to changes in the body, whereas the endocrine system mainly governs slow acting responses of long duration.

The Cardiovascular System

comprises the heart, blood vessels, and blood and acts as the transport system of the body. Blood carries oxygen from the lungs to the tissues and carbon dioxide from the tissues to the lungs. Blood also carries nutrients from the digestive tract to the individual cells so that the cells may extract nutrients for growth and energy. The blood carries waste products from the cells to the kidneys, from which the waste is excreted in the urine. It also carries hormones from the endocrine glands to other organs of the body and transports heat to the surface of the skin to control body temperature.

The temporal lobe

contains the cortical areas responsible for auditory and olfactory (smell) impulses, and the occipital lobe contains the visual cortex, which receives visual impulses.

The Frontal Lobe

contains the motor cortex, which coordinates voluntary movement.

The parietal lobe

contains the somatosensory cortex, in which sensations of touch, pain, temperature, and pressure are registered and interpreted.

Phagocytosis

is the process by which certain white blood cells (called phagocytes) ingest microbes. Phagocytes are usually overproduced when there is a bodily infection, so that large numbers can be sent to the site of infection to ingest the foreign particles. Antimicrobial substances are chemicals produced by the body that kill invading microorganisms. Interferon, hydrochloric acid, and enzymes such as lysozyme are some antimicrobial substances that help destroy invading microorganisms. The inflammatory response is a local reaction to infection. At the site of infection, the blood capillaries first enlarge, and a chemical called histamine is released into the area. This chemical causes an increase in capillary permeability, allowing white blood cells and fluids to leave the capillaries and enter the tissues; consequently, the area becomes reddened and fluids accumulate. The white blood cells attack the microbes, resulting in the formation of pus. Temperature response are the reddening, swelling, discharge, and clotting that result when you accidentally cut your skin and the sneezing, runny nose and teary eyes that result from an allergic response to pollen. Specific immunity is acquired after birth by contracting a disease or through artificial means, such as vaccinations. It operates through the antigenantibody reaction. Antigens are foreign substances whose presence stimulates the production of antibodies in the cell tissues. Antibodies are proteins produced in response to stimulation by antigens, which combine chemically with the antigens to overcome their toxic effects. Specific immunity is slower and, as its name implies, more specific than natural immunity. The lymphocytes involved in specific immunity have receptor sites on their cell surfaces that fit with one, and only one, antigen, and thus, they respond to only one kind of invader. When they are activated, these antigenspecific cells divide and create a population of cells called the proliferative response. Essentially, natural and specific immunity work together, such that natural immunity contains an infection or wound rapidly and early on following the invasion of a pathogen, whereas specific immunity involves a delay of up to several days before a full defense can be mounted. Figure 2.10 illustrates the interaction between lymphocytes and phagocytes.

chief functions of the kidneys

is to control the water balance in the body. For example, on a hot day, when a person has been active and has perspired profusely, relatively little urine will be produced so that the body may retain more water. On the other hand, on a cold day, when a person is relatively inactive or has consumed a good deal of liquid, urine output will be higher so as to prevent overhydration. Urine can offer important diagnostic clues to many disorders. For example, an excess of glucose may indicate diabetes, and an excess of red blood cells may indicate a kidney disorder. This is one of the reasons that a medical checkup usually includes a urinalysis. To summarize, the urinary system regulates bodily fluids by removing surplus water, surplus electrolytes, and the waste products generated by the metabolism of food.

The peripheral nervous system

made up of the somatic nervous system and the autonomic nervous system. The somatic, or voluntary, nervous system connects nerve fibers to voluntary muscles and provides the brain with feedback about voluntary movement, such as a tennis swing. The autonomic, or involuntary, nervous system connects the central nervous system to all internal organs over which people do not customarily have control.

The midbrain

major pathway for sensory and motor impulses moving between the forebrain and the hindbrain. It is also responsible for the coordination of visual and auditory reflexes.

The Role of Neurotransmitters

regulate nervous system functioning. Stimulation of the sympathetic nervous system prompts the secretion of two neurotransmitters, epinephrine and norepinephrine, together termed the catecholamines. These substances are carried through the bloodstream throughout the body, promoting sympathetic activation.

Platelets

serve several important functions. They clump together to block small holes that develop in blood vessels, and they also play an important role in blood clotting.

Disorders of the Renal System

nephritis involves the inflammation of the glomeruli in the nephrons of the kidneys that filter blood. Nephritis can be caused by infections, exposure to toxins, and autoimmune diseases, especially lupus. Nephritis is a serious condition linked to a large number of deaths worldwide. Another common cause of acute renal shutdown is tubular necrosis, which involves destruction of the epithelial cells in the tubules of the kidneys. Poisons that destroy the tubular epithelial cells and severe circulatory shock are the most common causes of tubular necrosis.

Menopause

of a variety of noxious symptoms that can occur during the transition into menopause, including sleep disorders, hot flashes, joint pain, forgetfulness, and dizziness, some women choose to take hormone therapy (HT), which typically includes estrogen or a combination of estrogen and progesterone. HT was once thought not only to reduce the symptoms of menopause but also to protect against the development of coronary artery disease, osteoporosis, breast cancer, and Alzheimer's disease. It is now believed that, rather than protecting against these disorders, HT may actually increase some of these risks. As a result of this new evidence, most women and their doctors are rethinking the use of HT, especially over the long term.

Angina pectoris

or chest pain, which occurs when the heart has insufficient supply of oxygen or inadequate removal of carbon dioxide and other waste products.

Myocardial infarction (MI)

or heart attack, which results when a clot has developed in a coronary vessel and blocks the flow of blood to the heart.

White Blood Cells

play an important role in healing by absorbing and removing foreign substances from the body. They contain granules that secrete digestive enzymes, which engulf and act on bacteria and other foreign particles, turning them into a form conducive to excretion. An elevated white cell count suggests the presence of infection.

The Limbic System

plays an important role in stress and emotional responses. The amygdala and the hippocampus are involved in the detection of threat and in emotionally charged memories, respectively. The cingulate gyrus, the septum, and areas in the hypothalamus are related to emotional functioning as well. Many health disorders implicate the brain. One important disorder that was overlooked until recently is chronic traumatic encephalopathy,

The Sympathetic Nervous System

prepares the body to respond to emergencies, to strong emotions such as anger or fear, and to strenuous activity. As such, it plays an important role in reaction to stress.

Lymphocytes

produce antibodies—agents that destroy foreign substances. Together, these groups of cells play an important role in fighting infection and disease.

release of catecholamines

prompts important bodily changes. Heart rate increases, the heart's capillaries dilate, and blood vessels constrict, increasing blood pressure. Blood is diverted into muscle tissue. Respiration rate goes up, and the amount of air flowing into the lungs is increased. Digestion and urination are generally decreased. The pupils of the eyes dilate, and sweat glands are stimulated to produce more sweat. These changes are critically important in responses to stressful circumstances. Chronic or recurrent arousal of the sympathetic nervous system can accelerate the development of several chronic disorders such as coronary artery disease and hypertension.

The Renal System

system consists of the kidneys, ureters, urinary bladder, and urethra. The kidneys are chiefly responsible for the regulation of bodily fluids; their principal function is to produce urine. The ureters contain smooth muscle tissue, which contracts, causing peristaltic waves to move urine to the bladder, a muscular bag that acts as a reservoir for urine. The urethra then conducts urine from the bladder out of the body. The anatomy of the renal system is pictured in Figure 2.8. Urine contains surplus water, surplus electrolytes, waste products from the metabolism of food, and surplus acids or alkalis. By carrying these products out of the body, urine maintains water balance, electrolyte balance, and blood pH. Of the electrolytes, sodium and potassium are especially important because they are involved in muscular contractions and the conduction of nerve impulses, among other vital functions.

The Absorption of Food

takes place primarily in the small intestine, which produces enzymes that complete the breakdown of proteins to amino acids. The motility of the small intestine is under the control of the sympathetic and parasympathetic nervous systems, such that parasympathetic activity speeds up metabolism, whereas sympathetic nervous system activity reduces it. Food then passes into the large intestine which acts largely as a storage organ for the accumulation of food residue and helps in the reabsorption of water. The entry of feces into the rectum leads to the expulsion of solid waste.

The Brain

the command center of the body. It receives sensory impulses from the peripheral nerve endings and sends motor impulses to the extremities and to internal organs to carry out movement.

Blood Pressure

the force that blood exerts against the blood vessel walls. During systole, the force on the blood vessel walls is greatest; during diastole, it falls to its lowest point. The measurement of blood pressure includes these two pressures. Blood pressure is influenced by several factors. The first is cardiac output—pressure against the arterial walls is greater as the volume of blood flow increases. A second factor is peripheral resistance, or the resistance to blood flow in the small arteries of the body (arterioles), which is affected by the number of red blood cells and the amount of plasma the blood contains. In addition, blood pressure is influenced by the structure of the arterial walls: If the walls have been damaged, if they are clogged by deposits of waste, or if they have lost their elasticity, blood pressure will be higher. Chronically high blood pressure, called hypertension, is the consequence of too high a cardiac output or too high a peripheral resistance.

Cerebral Cortex

the largest portion of the brain, involved in higherorder intelligence, memory, and personality. Sensory impulses that come from the peripheral areas of the body are received and interpreted in the cerebral cortex. The cerebral cortex consists of four lobes: frontal, parietal, temporal, and occipital. Each lobe has its own memory storage area or areas of association. Through these complex networks of associations, the brain is able to relate current sensations to past ones, giving the cerebral cortex its formidable interpretive capabilities.

As Food Progresses to the Stomach

to the duodenum (the intersection of the stomach and lower intestine), the pancreas becomes involved in the digestive process. Pancreatic juices, which are secreted into the duodenum, contain enzymes that break down proteins, carbohydrates, and fats. A critical function of the pancreas is the production of the hormone insulin, which facilitates the entry of glucose into the bodily tissues. The liver also plays an important role in metabolism by producing bile, which enters the duodenum and helps break down fats. Bile is stored in the gallbladder and is secreted into the duodenum as needed.

Other major disorders of the cardiovascular system include the following

∙ Congestive heart failure (CHF), which occurs when the heart's delivery of oxygen-rich blood is inadequate to meet the body's needs. ∙ Arrhythmia, irregular beatings of the heart, which, at its most severe, can lead to loss of consciousness and sudden death.