Bio 530 Module 4

colon cells and glands

Because there are no villi in the colon, all the lining cells are in the glands. The same cells are found here as in the small intestine except you will note that there are no enzyme producing cells for digestion. The ratio of goblet cells to lining cells is very high. The absorptive cells are only located at the lumen surface. These cells participate in the absorption of water that helps to compact the feces.

overview

First an overview of the respiratory system is presented to emphasize the parts of the respiratory tract that conduct air and the parts that act upon the air to exchange carbon dioxide for oxygen. Thehistologicalstructureofthe respiratory epithelium and how it forms an escalator to trap and move foreign substances like dust and bacteria out of the lung, and, the histology of the air-blood diffusion membrane (barrier) of the alveoli is emphasized. Three examples of pathology of the respiratory tract and lung are also included in this lecture, namely, cystic fibrosis, squamous metaplasia due to smoking, and pneumonia.

appendix

Observe the gross anatomy illustration of the cecum and the appendix. The arrows indicated the opening from the cecum into the appendix and the worm- like shaped appendix. Histologically, the appendix resembles the colon in every way except for two important differences. First the appendix outer layer of the muscularis externa is continuous, i.e. no taenia coli. Second, the appendix has many large and prominent lymphatic nodules in its mucosa and submucosa.

bicarbonate flux

Observe the relationship between the lumen, the surface epithelial cells, the mucus layer, the gastric pit, and the cells of a single tubular fundic gland. To prevent self-digestion, the stomach utilizes the other ion in the breakdown of carbonic acid- the bicarbonate ion. After release into the interstitium, the bicarbonate is taken up in the capillary beds which transport it to the apical region of the pits. Here it is released for incorporation into the mucus layer of the stomach to help neutralize the effects of the HCl in the lumen. The alkaline bicarbonate in combination with mucus secreted by mucus neck cells and surface lining cells of the stomach mucosa, in normal conditions, successfully neutralizes the acid at the surface lining so that the delicate cells of the gastric mucosa are not destroyed.

the large intestine (colon)

The colon begins at the end of the ileum at the ileocecal junction and extends to the anus. It is about 5 feet long. The colon consists of 4 parts: 1) the ascending colon (A), 2) the transverse colon, 3) the descending colon, and 4) the sigmoid colon (s- shaped). The enlargement on the left shows the detail of this junction. Observe that the appendix extends out of the cecum. The appendix (also vermiform appendix) is a worm like structure (vermiform is a Latin adjective used to denote this shape). The cecum of humans is small and rudimentary; however, in animals that are herbivores the cecum is very large. The large intestine differs most obviously from the small intestine in that it is much wider and that the longitudinal layer of the muscularis externa is reduced to 3 strap-like structures known as the taenia coli as will be illustrated.

bladder epithelium

The epithelium of the urinary bladder is transitional epithelium. It is a very unique structure arrangement. The surface cells are dome shaped when the bladder is not full or stretched. These cells are called facet cells as they face and border the lumen. We shall examine these cells in more detail.

The esophagus

The esophagus connects the pharynx with the stomach. It is lined with stratified squamous non-keratinized epithelium that provides a smooth surface for passage swallowed food. The technical term for swallowed food is 'bolus'.

Paneth Cells - secrete lysozyme

The arrows point to the bright red granules of the Paneth cells in the intestinal gland (crypt of Lieberkuhn). The granules contain mostly lysozyme which aids in keeping the bacterial flora in check in the lumen of the intestine. How can you differentiate a Paneth cell from a mast cell (both have bright red granules)? Ans: Paneth cells are always in the intestinal epithelium while mast cells are in the lamina propria. Mast cells have their nucleus located in the center of the cell.

submucosa supports the plicae

The blue ovals outline plicae circulares that illustrates the submucosal support of these structures in a histological section.

Classic Liver Lobule Central Vein & Portal Area

The center of a classic liver lobule is the central vein. The peripheral extent of the lobule is determined by lines drawn between the portal areas that contain the hepatic arteries, bile ducts and portal veins. In human liver there is very little connective tissue surrounding the structures in the portal areas and even less extending from one portal area to another. One has to visualize the liver lobule by connecting the portal areas drawing imaginary lines as was done in this specimen. Observe that only 4 portal areas could be observed as is often the case. It is very difficult to find an ideal liver lobule with 6 portal areas surrounding a central vein in a typical histological section. An enlargement of the central vein area shows the central vein that is lined by endothelial cells as are the sinusoids that connect to the central vein. An enlargement of a portal area shows a portal vein containing blood cells, a bile duct lined by simple cuboidal epithelium and a hepatic artery. Observe that there is very little connective tissue in this portal area. To be precise the hepatic artery in the portal areas surrounding the central vein in a liver lobule should be called a hepatic arteriole because technically it is an arteriole. Text books and the literature often just refer to the vessel as hepatic artery.

Mucociliary escalator: cilia and layer of mucus on surface of epithelium

The ciliated cells and the goblet cells create an escalator belt, so-to-speak. The layer of mucus with just the correct amount of water forms a "belt" of mucus moved by the billions of cilia that rids the airway of particles consisting of dust, bacteria and other particulate matter. This moving belt of mucus is called the 'mucociliary escalator'. Mucus moved by billions of coordinated cilia In the yellow frame is a view of the apical ends of a series of ciliated epithelial cells with a layer of mucus at the tips of the cilia as seen in a scanning electron microscope. The cilia constitute the motor that moves the mucus (similar to a motor moving an escalator belt or steps). The cilia move in coordinated waves similar to the way in which winds sweeps over a wheat field where you can see the wheat bending in waves as the wind moves over the field. In a wheat field, the wind is the motor. In the case of respiratory epithelium the billions of cilia are the motor that moves the mucus layer that has entrapped foreign substances.

the esophagus organization

The esophagus is a hollow organ consisting of 4 layers. If the tube is cut across, the first layer seen surrounding the lumen is the mucosa composed of epithelium, lamina propria and a smooth muscle layer called the muscularis mucosa. The next layer is composed of loose connective tissue that may contain glands and adipose tissue and it is termed the submucosa. The next layer is composed of muscle organized in two layers, an inner circular oriented and an outer longitudinal oriented layer. The muscularis externa of the upper 1/3 of the esophagus is striated skeletal muscle, in the middle 1/3 it is a mixture of striated skeletal and smooth muscle while in the lower 1/3 it is all smooth muscle. The outermost layer is composed of loose connective tissue and is named the adventitia.

gingiva and teeth

The extent of the gingiva is bounded by the dotted lines. The arrow on the left tooth indicates the point at which the dentist probes to determine if there is a normal depth before the gingival epithelium is fused to the enamel of the tooth. This is called the gingival sulcus. An abnormally deep gingival sulcus places the patient in danger of having infection in the tissue below the epithelium surrounding the tooth. The gingival mucosa is masticatory mucosa with a parakeratinzed epithelium. Observe the teeth. Normally the exposed surfaces of the tooth are covered with enamel as can be seen here.

gallbladder

The gall bladder is a pear-shaped, distensible sac with a volume of about 50 ml in humans. It is attached to the visceral surface of the liver.

gallbladder wall structure

The gallbladder is a hollow organ that has three different layers surrounding its lumen. The mucosa does not have a muscularis mucosa. The simple columnar epithelium of the mucosa has NO GOBLET CELLS. The folded mucosa resembles villi, but these are not villi. There are no glands at the base of the folds. The absence of a muscularis mucosa, goblet cells and intestinal glands helps distinguish the gall bladder from the jejunum and ileum of the small intestine. The muscularis externa contains bands of smooth muscle that function to squeeze bile out of the gallbladder into the duodenum via of the common bile duct. A serosa wraps the gallbladder.

the salivon

The secretory unit of a salivary gland is composed of the acinus, the intercalated duct, the striated duct and the excretory duct. Another term for the secretory unit is 'salivon'. The diagram illustrates the variation in function of each component of the secretory units in the parotid, submandibular or sublingual gland. The initial product whether mucous, serous or mixed is synthesized and secreted by the cells of the acinus. The intercalated ducts secrete bicarbonate ion into the duct and absorb chloride ions. Clearly, the parotid gland contributes most to this function. Striated ducts reabsorb sodium from the lumen and add potassium. The submandibular gland contributes most to this function. The excretory ducts in all three glands have the same level of function and that is simply to transport the saliva to the oral cavity.

Small Intestine Surface Area Amplification Structures

The small intestine is designed at several levels to provide a large surface area for food undergoing digestion to have maximal contact with the surface epithelial cells for absorption. First the small intestine is very long, including the duodenum, a total of nearly 21 feet. Second, the mucosa, including all three layers, is folded with the submucosa at the core. These folds are called Plicae Circulares (singular - plica circularis). Observe that the jejunum has the largest number of folds per unit length and this is the segment of the small intestine where most of the amino acids, fatty acids, glycerol, glucose and other nutrients are absorbed.

intestines gross anatomy

The small intestine is divided into three structural parts: 1) the duodenum approximately 10 inches in length, 2) the jejunum approximately 8 feet in length and 3) the ileum approximately 12 feet in length. The colon consists of ascending, transverse and descending parts and is about 5 feet long. The diameter of the small intestine averages 1 inch compared to 2.5 inches for the colon. Although the small intestine is much longer than the large intestine (typically around 3 times longer), it gets its name from its comparatively smaller diameter. As a simple tube the length and diameter of the small intestine would have a surface area of only about 0.5 m2. However, special structures that you learn about like villi, microvilli and folds of the mucosa increase the surface area about 500 times greater than a smooth bore tube would have. The surface area of the small intestine is on the order of 200 square meters (the size of a tennis court).

stomach

The stomach begins at the esophageal-stomach junction and ends at the stomach-duodenal junction. The stomach has mucosal glands but does not have any submucosal glands

stomach histology organization

The stomach is a hollow organ with four distinct layers making up its wall. The mucosa is composed of simple columnar epithelium the cells lining the surface, gastric pits and glands the cells of which are continuous with the lining epithelial cells, a lamina propria of loose connective tissue that surrounds the gastric mucosal glands, the submucosa composed of loose connective tissue with blood vessels, nerves and adipose tissue, the muscularis externa that, unlike the esophagus, the smooth muscle of the stomach muscularis externa is arranged in three layers. The outermost layer is a serosa.

Respiratory Region Nasal Cavity Mucosa

This slide illustrates the mucous membrane of the respiratoryregionofthenasalcavity. The pseudostratified ciliated columnar epithelium of the mucous membrane contains goblet cells that provide mucus and the serous glands located in the lamina propria produce a protein rich watery secretion that reaches the surface via ducts. Throughout the respiratory tract, GI tract, urinary tract, and reproductive tracts there is a close association of the epithelial lining with the layer of loose connective tissue just beneath (called the Lamina Propria). The epithelium and this layer of connective tissue is known as the Mucosa, which also can be appropriately referred to as a Mucous Membrane, a named derived from the fact that the cells of the mucosa produce mucus (Mucus is a noun, Mucous is an adjective).

Pattern of Ciliary Force Nasal Cavity

This slide illustrates the pattern of ciliary movement of the mucus layer in the nasal cavity. The beat of the cilia in the nasal cavity is orchestrated to move the layer of mucus containing any contaminates from the environment toward the nasal pharynx.

cilium

This slide is intended to remind you of the structure of a single cilium. Note how the cilium is anchored into the apical part of the ciliated cell. Observe the internal structure of the cilium consisting of 9 pairs of microtubules at the perimeter and two microtubules in the center - correctly referred to as the '9 + 2" arrangement of microtubules. The next slide will illustrate the internal structure of a cilium in a transmission electron micrograph.

nephrons and uriniferous tubules

nephrons component -renal corpuscle Bowman's capsule Containing a glomerulus Proximal Convoluted Tubule Loop of Henle Distal Convoluted Tubule Connecting Tubule Uriniferous Tubule Components A nephron a collecting duct to which it connects A nephron consists of the renal corpuscle (made up of Bowman's capsule enclosing several capillary loops called a glomerulus), a proximal convoluted tubule, a loop of Henle (consisting of a descending straight portion of the thick proximal tubule, the thin segment of tubule, and the ascending straight portion of the distal tubule) and the tubule segment that connects to a collecting duct. From Bowman's capsule and it lumen throughout to the collecting duct the lumen is continuous between the components of the nephron. The nephron is the functional unit of the kidney. The nephron and the collecting duct that it connects to make up the uriniferous tubule. Many nephrons connect to a single collecting duct. The number of nephrons for each kidney in normal adult humans ranges from as low as 230,000 to over 2 million. Studies have suggested that an inborn deficit of nephrons predisposes an individual to acquired kidney disease, including hypertension.

cross section of a trachea with a light micrograph at low mag

ory Organs Observe that the wall of the trachea is supported by hyaline cartilage that is C-shaped with the ends of the cartilage always facing the posterior aspect. A significant bundle of smooth muscle cells spans the space between the ends of the cartilage. When this muscle contracts the trachea lumen diameter decreases causing an increase in the resistance of airflow. The trachea is lined with the respiratory type of epithelium (pseudostratified ciliated columnar epithelium). Between the epithelium and the cartilage and also distributed among the smooth muscle are glands composed of serous and mucous cells.

stomach muscle

3 layers of smooth muscle Outer longitudinal Middle circular Inner oblique Pyloric sphincter Anatomic and physiologic Parasympathetics inhibit (relax) Sympathetics constrict The stomach has three layers of smooth muscle; an outer arranged longitudinally, a middle layer arranged in a circular direction around the stomach, and an inner layer that has fibers that run obliquely to the long axis of the stomach. At the pyloric end just before the stomach joins the duodenum the circular muscle layer is dominate forming a sphincter that is under the control of the autonomic nervous system. Parasympathetic fibers cause the sphincter muscles to relax thereby allowing the stomach contents to flow into the duodenum. Sympathetic fibers constrict the sphincter muscles preventing entrance of stomach contents into the duodenum. Parasympathetic action facilitates digestion. Sympathetic action inhibits digestion.

nerve plexi in the intestine

Auerbach's plexus myenteric between the 2 layers of smooth muscle of muscularis externa Meissner's plexus submucosal Within the submucosa The GI tract is controlled by the autonomic nervous system(sympathetic/parasympathetic). Nerveplexi are located in two regions: the myenteric plexus (Auerbach's) is situated between the layers of smooth muscle in the muscularis externa layer and the Meissner's plexus is located in the submucosa.

Liver Blood Supply/Drainage & Bile Secretion/Storage

Blood Supply Hepatic artery from the aorta Oxygenated blood to supply parenchyma and stroma Portal Vein from the intestines 75% of blood supply from portal vein Brings absorbed nutrients Blood drainage All by the hepatic veins Bile secretion and storage Bile is secreted by liver cells Drains to the intestines by common bile duct Concentrated and stored in the gall bladder This drawing illustrates the blood supply/drainage & the storage and drainage of bile from the liver. Observe that the liver has two vessels supplying it with blood and one draining it. One is the hepatic artery supplying the liver with oxygen and the other is the portal vein that brings blood from the intestines carrying molecules absorbed after digestion to the liver. Blood is collected / drained from the liver by the hepatic vein that returns blood to the heart. Bile is collected from the liver and stored in the gallbladder where it is concentrated and released on demand into the duodenum via the common bile duct. From this point on in the lecture please take note of the names of two vessels and a duct - 1) portal vein, 2) hepatic (portal) artery (arteriole), and 3) bile duct. As you learn the histology of the liver you will see that these three structures form a 'triad' that is integral in understanding liver histology.

the portal system

Brings nutrient rich blood from gut Accounts for high incidence of liver metastasis from cancers of the intestine. This is an illustration of the portal system that brings blood from the intestine and delivers it to the liver. The portal system begins in capillaries in the lamina propria of the intestine, continues in the different portal veins draining different parts of the intestine and ends in sinusoids in the liver. The blood is rich is nutrients from the intestine. Malignant cancer in the intestine can easily metastasize to the liver by the portal system.

lower respiratory tract conducting airways

Bronchial Tree Primary Bronchi Respiratory Epithelium Cartilage Plates & Seromucous glands Complete Layer of Smooth Muscle Secondary Bronchi Same as Primary, less cartilage more muscle Bronchioles 0.5 - 1.0 mm in diameter Terminal portion of conducting airways No cartilage but complete layer of smooth muscle No glands but goblet cells persist in epithelium Epithelium includes Clara cells The conducting airways continue after the trachea into branches of the trachea called the right and left primary bronchi. These bronchi branch in severalgenerations. Allofthebronchicontain cartilage but it is in the form of plates rather than C-shaped rings as was the case in the trachea. After several generations of bronchi, the diameters of which become smaller and smaller, the conducting airways continue as bronchioles that contain no cartilage but have a continuous coat of smooth muscle as part of their wall structure.

Duodenum Brunner's Glands - Intestinal Glands - Villi

Brunner's glands in the submucosa of the duodenum secrete mucus to neutralize acid from stomach Villi are projections of the mucosa into the lumen to increase surface area Intestinal glands are simple tubular glands located in the mucosa The duodenal mucosa is organized into villi and intestinal glands. The submucosa contains Brunner's Glands (mucous glands). This enlarged view of Brunner's glands displays the mucous cells of Brunner's glands that secrete mucus into the lumen of the duodenum. They produce a highly alkaline secretion which helps to neutralize the acid contents coming from the pyloric region of the stomach. The only other area of the GI tract where you will find submucosal glands is in the esophagus. Villi are long projections into the lumen of the intestine. This enlargement illustrates several villi, one of which is labeled. Each villus is covered by simple columnar epithelium with a mix of absorptive cells with many microvilli and goblet cells. Beneath the epithelium is a core of loose connective tissue containing fibroblasts, lymphocytes, plasma cells, blood vessels and a lymphatic capillary (a lacteal). Intestinal glands are simple tubular glands that are included as a part of the mucosa, not the submucosa. They are mucosal glands. Details of villi and intestinal glands are presented in the following slides.

larynx

Cartilaginous Components Hyaline Cartilage: thyroid, cricoid, arytenoid Elastic Cartilage: cuneiform, corniculate, epiglottis and tip of arytenoids Mucosa Epithelium & Loose Connective Tissue Vocal Cords False - respiratory epithelium True - stratified squamous non- keratinized epithelium Vocal ligament: dense band of elastic fibers Vocal muscle: thyroarytenoid (striated muscle) There are three components of the Larynx; the wall with cartilage for support, the mucosa and the vocal cords. The larynx is lined with pseudostratified ciliated columnar epithelium everywhere except over the true vocal cords. The constant rush of air and vibration of these cords induces an epithelial reaction early in life transforming that epithelium into stratified squamous non-keratinized epithelium.

summary

This lecture began with a presentation of the general plan of organization of the wall of the intestines. The small intestine was presented with explanations and illustrations of the difference between plicae circulares, villi and microvilli. The cells of the intestinal gland were presented and how they are renewed by stem cells dividing in the crypts of Lieberkuhn. The histology of the colon was presented that included illustrated examples of colon polyps and adenocarcinoma of the colon. The histology of the appendix, rectum and anal canal were presented emphasizing their similarities and differences.

Esophagus Nerve Plexi & Ganglia

Enteric Nervous System Meissner's plexi Located in the submucosa Sympathetic terminal nerve fibers Parasympathetic ganglia and nerve fibers Auerbach's (myenteric) Plexi Located between muscularis externa layers Sympathetic terminal nerve fibers Parasympathetic ganglia and nerve fibers Nerves and ganglia of the autonomic nervous system function in the GI tract to cause muscle contraction to move food and to control blood flow through action on the smooth muscle of arteries and arterioles. The autonomic nerves and ganglion found in the GI tract are known as the enteric nervous system. In this slide two ganglia and nerve plexi of the enteric nervous system will be presented. Meissner's plexi are located in the submucosa. If an area as enclosed by the rectangle is enlarged the cell bodies of parasympathetic neurons can be seen. The nerves present would be both sympathetic and parasympathetic. The sympathetic nerve terminals would have arisen from neuron cell bodies alongside the spinal cord in paraganglia. The parasympathetic nerve fibers would be connected to the cell bodies of parasympathetic neurons as seen here. The other plexi are Auerbach's (also myenteric) located between the inner and outer layers of the muscularis externa. If an area as outlined is enlarged the plexi with neuron cell bodies would look like this. In both the submucosal Meissner's and the Auerbach's (myenteric) plexi, the sympathetic innervation is inhibitory to peristalsis (the wave like contraction of muscle down the GI tract to propel the food bolus and digesting food). The parasympathetic component in both plexi facilitates peristalsis.

Liver to Anatomical Location & General Information

Location Upper right quadrant abdomen, on top of stomach, right kidney & intestines - small part in upper left quadrant General Information Weighs 1500 grams Largest internal organ Performs on order of 500 functions Liver functions remain normal even if 70% is removed Only organ in the body that can regenerate itself Small remnants of liver grow back to normal size within a few weeks The liver is located in the upper right quadrant of the abdomen as you can see in this photograph of a 'transparent' man found on the Internet as a part of an ABC news report. The liver is the largest mass of glandular tissue in the body. The liver performs over 500 functions. Even if 70% of the liver is destroyed it can maintain normal function. It is the only organ in the body that can regenerate itself. Observe the encircled light pink areas in the liver of this man. The light pink areas in this liver of the 'transparent' man suggest fatty change due to alcohol. Too much beer / liquor drinking causes liver cells to be engorged with fat that compromises liver function. This eventually leads to cirrhosis (scar tissue) that permanently damages the liver. Cirrhosis can eventually overcome the liver's ability to regenerate. Liver cancer and infection of the liver are also very damaging to the liver. While the liver has the ability to regenerate itself, it does have limits. For example bacterial infection of the liver can completely overwhelm it. The blood sinuses of the liver contain cells that have great phagocytic properties and normally clear the blood coming from the intestines of any bacteria in one pass of the blood through the liver. However, interestingly enough, chronic alcohol drinking depresses the function of these cells that sets the stage for vulnerability to infection.

trachea

Mucosa Respiratory Epithelium and lamina propria Submucosa Serous-Mucous Glands Fibromusculocartilaginea C shaped hyaline cartilage rings and smooth muscle Adventitia Loose connective tissue The next segment of the conducting airways is the trachea. The trachea is a hollow organ consisting of four layers of tissue- the mucosal layer, submucosal layer, fibrous-muscular- cartilage layer and an outer layer of loose connective tissue, the adventitia.

overview of urinary system

Paired Kidneys Excretes waste products & water (urine), control water & electrolytes in tissues, maintains pH of blood, contributes to the regulation of blood pressure and helps to regulate the density of erythrocytes in circulating blood (hematocrit) Paired Ureters Delivers urine made by the kidneys to the urinary bladder Urinary Bladder Stores urine Urethra (presented in lectures on male and female reproductive tract and organs) Delivers urine to the external environment. The urinary system consists of three organs - kidneys, right and left ureters and the urinary bladder. The kidneys have multiple functions that include excreting waste products, controlling hydration of the cells and tissues of the body, maintaining the proper concentration of electrolytes like sodium chloride, calcium chloride etc, playing an important role in maintaining normal blood pressure and even secreting a hormone, erythropoietin, that stimulates the bone marrow to produce and release more erythrocytes if the hematocrit falls below the normal range. Under hypoxic conditions such as going to a high altitude, an increased level of erythropoietin is secreted by cells in the kidney that causes the production of more red blood cells. This helps one adapt to high altitude by increasing the number of oxygen carrying cells. The ureters deliver urine to the urinary bladder, the urinary bladder stores urine to be later expelled by the act of urination, and the urethra is the conduit that carries the urine outside of the body. The urethras of the male and female will be presented in the lectures on the male and female reproductive tracts and organs.

liver functions

Produces most of plasma proteins Albumins, lipoproteins, glycoproteins, prothrombin, fibrinogen, nonimmune alpha and beta globulins Stores and converts vitamins and iron Vitamins A, D and K Clears blood of undesirable chemicals/drugs and microorganisms Oxidation and conjugation of chemicals/drugs to make them water soluble so they can be secreted by the kidney E-coli bacteria, for example, that can gain entrance to blood by defective intestine epithelial lining, are removed by special cells lining the blood vessels of the liver Secretes bile into the intestine. Bile is essential for digestion of fats Converts and stores extra sugar (glucose) in the form of starch (glycogen) that can be returned to glucose in times of starvation With 500 different functions of the liver it is not possible to list them all. These presented are some of the most important functions.

summary

This lecture began with a presentation of the general plan of the gastrointestinal tract emphasizing the four layers: mucosa, submucosa, muscularis externa and serosa / adventitia components. Next the oral cavity was presented as having an entrance, the oral vestibule, bounded by the lips and the teeth, and the oral cavity proper, bounded by the hard palate, oropharynx, teeth and mucosal covered muscle beneath the tongue forming the floor of the oral cavity. Oral cavity and mouth are synonymous Then the histology of the tongue was presented that included the taste buds and their distribution throughout the tongue. The geographical location of the taste modalities of sweet, salty, bitter & sour was shown on the tongue. The location, duct openings and histology of the parotid, submandibular and sublingual glands were presented with a comparison of the histology in the different glands. Finally, the cellular basis of immune function by the salivary glands was presented along with the composition of saliva

rectum- anal canal- anus

Rectum Histology is similar to colon Simple columnar epithelium with mucosal glands Anal Canal Epithelium transitions from simple columnar to stratified squamous non-keratinzed Hemorrhoidal veins in the lamina propria The rectum (from the Latin rectum intestinum, meaning straight intestine) is the final straight portion of the large intestine terminating in the anus. The rectum has a mucosa similar to the colon - simple columnar epithelium at the surface with tubular intestinal mucosa glands containing many goblet cells. The submucosa, muscularis externa and serosa are also similar to the colon. The human rectum is about 12 cm long. Its caliber is similar to that of the sigmoid colon at its commencement, but it is dilated near its termination, forming the rectal ampulla. Just beyond the rectal ampulla, the mucosa is folded forming the anal columns. The mucosa continues as in the rectum, however, at a certain line called the pectinate line, the epithelium begins to transition from simple columnar to stratified squamous non-keratinized epithelium. In the transition zone for a short segment the epithelium is stratified columnar. At the end of the anal canal is an opening, the anus. At this point the epithelium becomes slightly keratinized and then merges with the skin epidermis that is characteristically keratinized. Observe the large veins in the lamina propria of the anal canal. These are the internal hemorrhoidal veins that frequently become so distended that they cause the mucosa to protrude into the lumen reducing its diameter. They can rupture to cause temporary bleeding. The rectum acts as a temporary storage site for feces. As the rectal walls expand due to the materials filling it from within, stretch receptors from the nervous system located in the rectal walls stimulate the desire to defecate. If the urge is not acted upon, the material in the rectum is often returned to the colon where more water is absorbed. If defecation is delayed for a prolonged period, constipation and hardened feces results. When the rectum becomes full, the increase in intrarectal pressure forces the walls of the anal canal anal apart, allowing the fecal matter to enter the canal. The rectum shortens as material is forced into the anal canal and peristaltic waves propel the feces out of the rectum. The internal and external sphincter allows the feces to be passed by muscles pulling the anus up over the exiting feces.

respiring airways

Respiratory Bronchioles Alveoli alternating with ciliated cuboidal epithelium Interlacing network of smooth muscle Alveolar Ducts Wall is a series of alveoli interrupted by thin bands of smooth muscle lined by squamous cells Alveolar Sacs Group of alveoli opening into a common area (an atrium) Alveoli Thin walled polyhedral sacs open on one side Dense capillary network Lined by simple squamous and secretory cells Note the airways generated and supplied by a respiratorybronchiole. Respiratorybronchioles and alveolar ducts are like hallways having an increased number of open and wide doors into rooms (alveoli) the further you walk down them. An alveolar sac is at the end of the road, consisting of the terminal portion of the airways, a large room with many alcoves (alveoli).

salivary gland immune function

Salivary Glands contain antibodies Salivary glands participate in the humoral immune response Source of antibodies are Plasma Cells Located in the connective tissue Secrete secretory immunoglobulin A (IgA) Acinar cells have a secretory glycoprotein that binds with IgA from the plasma cell The secretory molecule aids in the passage of IgA from the plasma cell through the acinar cell to the lumen salivary glands contribute to an immune response in the oral cavity. Plasma cells are distributed throughout the connective tissue surrounding the secretory acini of the salivary gland. Observe three plasma cells that are indicated in this specimen of a parotid gland. Therefore by the presence of plasma cells that secrete antibodies saliva contains antibodies and salivary glands participate in the humoral immune response. The antibody secreted by plasma cells in this case is called 'secretory IgA'. When secretory IgA leaves a plasma cell it binds to a secretory glycoprotein molecule that resides in the basal membrane of acinar cells. This molecule aids the transport of IgA through the acinar cell by facilitating the endocytosis of the antibody at the acinar cell basal surface and the exocytosis of the antibody to the lumen of an acinus. The mouth is an endangered entrance into the gastrointestinal tract. Salivary gland antibodies function to neutralize foreign bacteria before they enter the esophagus.

stomach regions

Stomach is J shaped 2 surfaces anterior & posterior 2 curvatures lesser & greater 4 regions cardiac fundus body pylorus The stomach is J shaped. It has two curvatures, a lesser and a greater. It has two surfaces, anterior (facing you) and posterior. It has 4 parts: 1) the cardiac region where the esophagus joins the stomach 2) the fundus that is the blind top of the stomach 3) the body region that makes up most of the mass of the stomach and 3) the pyloric region the end of which connects to the duodenum.

summary

The lecture began by presenting an overview of the respiratory system in which the organs that encounter breathed in air from the nose to the alveoli within the lung were outlined. Next, the specialize epithelium lining the nasal cavity, larynx, trachea, bronchi and larger bronchioles was presented along with the structure of the respiratory epithelium. The role of its specialized cells-goblet cells and ciliated cells, were explained as to how they create a type of escalator, the muco-ciliary escalator to rid the lung of bacteria, viruses, dusts and other foreign substances. Cystic fibrosis was given as an example for what occurs when this escalator cannot function properly. Then, the histology of the conducting airways was presented. The induction of metaplasia in the respiratory epithelium by chronic smoking was illustrated and explained. Finally, the respiring airways and the specific structure of alveoli, including the blood-air diffusion membrane was presented. The lecture concluded with a demonstration of histopathology of pneumonia

summary

This lecture began with a presentation of an important concept: an explanation of the difference between a mucosal gland (glandular cells within the mucosa epithelium) and a submucosal gland (glandular cells within the submucosa) Next the histology of the esophagus was presented emphasizing the non- keratinized stratified squamous epithelium and the presence of submucosal glands. Squamous cell carcinoma was presented as an example of pathology of the esophagus. The stomach was presented next with an explanation of how the secretions of mucus and bicarbonate protect the stomach mucosa from self digestion. Each of the cell types that make up the branched tubular glands of the stomach were presented and their function given.

summary

This lecture began with a presentation of liver histology emphasizing the lobular organization of the liver. The blood supply and drainage of the liver were described and illustrated emphasizing the portal triad that consists of the hepatic artery, portal vein and bile duct. The relationship between the neighboring hepatocytes was presented and bile duct formation was demonstrated. The effect of fatty change on liver histology and function was presented and illustrated. The three ways to view liver organization, the classic lobule, the portal lobule and the acinus were presented to emphasize different functions of the liver. Gallbladder histology was presented with the emphasis on its role in taking up water to store bile in a concentrated form until needed for fat emulsification in the duodenum Finally, the histology of the endocrine and exocrine parts of the pancreas was presented.

summary

This lecture began with an overview of the urinary system., followed by a presentation of the location and gross structure of the kidneys. Next the renal lobe was illustrated and defined in the context of a low magnification histological section through the kidney. Then, the blood vessels that enter, course through and leave the kidney were illustrated and the sequence of blood flow was described. After that, the segments and histology of the nephron were presented. The lecture continued with a presentation of the renal corpuscle showing the relationship of its parts; Bowman's capsule and the glomerulus. Following that the filtration apparatus, the glomerular filtration membrane was presented. The special arrangement involving the end of the distal tubule (macula densa) and afferent arteriole, the juxtaglomerular appratus was presented. Finally, the histology of the urinary tract was illustrated and explained.

Vestibule of the Oral Cavity Entrance to Oral Cavity Proper

Transition from external keratinizing stratified squamous epithelium to inner non-keratinized squamous epithelium Inner surface of cheek is referred to as the buccal region As we begin it is helpful to understand the transition that takes place as we enter the oral cavity / mouth. Here we see the oral vestibule that is defined as the area between the teeth and the lips. The area between the inner surface of the cheeks and teeth is an extension of the oral vestibule, but has a different name, the buccal region. A dentist describes the front surface of the upper and lower incisor teeth as the labial surface. The outer surface of the molar teeth is termed the buccal surface. The keratinized epithelium of the skin is oily. At the vermilion border the epithelium changes to a lining of non-keratinized epithelium that is wetted with a mixture of water and mucus.

tongue

Uvula (U) Palatine Tonsil (PT) Tongue Body (ant 2/3) Median sulcus (MS) Papillae Filiform (FI) Fungiform (FU) Circumvallate (V) The tongue occupies a large part of the oral cavity. When the tongue is protruded from the mouth as during an examination by a physician, the uvula can be seen as a downward projection from the soft palate in the midline. On either side about at the level of the uvula are palatine arches in which the palatine tonsils are located. Filiform papillae cover most of the tongue. They appear whitish. Fungiform papillae are not as numerous and they appear as tiny red circular areas. Circumvallate papillae are located at the border between the body and the root of the tongue. They are round and large structures that project a little above the surface. One can be seen back on the left.

nasal cavities

Vestibule Skin Sebaceous Glands & Hair Follicle Nasal Cavity Respiratory Region Pseudostratified ciliated columnar Epithelium Mucous & Serous Glands Nasal Cavity Olfactory Region Tall Columnar Epithelium with nerve cells GlandsofBowman: Serous The entrance into the right and left nasal cavities are called the nasal vestibules and they are lined with skin that includes sebaceous glands and hair. The respiratory region of the nasal cavities constitutes the largest area and it is lined with a mucous membrane consisting of pseudostratified ciliated columnar epithelium and loose connective tissue with mucous and serous glands in the lamina propria. A small area in each nasal cavity is lined by simple columnar epithelial cells with many interposed bipolar neurons that function to transduce chemical substances inhaled and dissolved into the surrounding water environment into a neuronal signal that the brain interprets as various odors. Serous glands in the lamina propria produce a watery secretion that keeps the components of the odors inhaled in solution.

lip histology

A histological section through the lower lip would appear Histology of the Lips oral vesitibule side: tooth, consisting of stratified squamous non- red area of the lip vermilion border skin side: epidermis, dermis includes hair follicles, sweat and sebaceous glands enamel (yellow) covering dentin gingiva (gum) surrounding the tooth keratinizing epithelium minor salivary glands orbiculis oris muscle (lip muscle consisting of striated muscle cells) S i d Lip: Histology Specimen red area tall papillae of red area red area of lip vermillion border mucous - serous cells lip muscle (orbiculus oris) gland SSNK propria labial labial lamina hair follicles & sebaceous glands duct with duct oral vestibule gland skin sebaceous glands surface like this specimen stained with hematoxylin and eosin. l Observe the oral vestibule and skin sides, and, the centrally e revealing deep invaginations of the epithelium between projections of the lamina propria connective tissue, a 1 structure arrangement that gives the red area its color. Still, a higher magnification reveals that the epithelium is very slightly keratinized because of exposure to the atmosphere 3 and sun. Next we examine the oral vestibule side. At this first magnification we see the mucosa, a duct passing located lip muscle (orbiculus oris muscle). The muscle is striated skeletal muscle and, as everyone knows is controlled at will. We will examine the three areas outlined in greater detail beginning with the red area of the lip through the mucosa and the outline of a minor salivary gland. At greater magnification the epithelium is seen to be stratified squamous non-keratinizing. If then the minor salivary gland is enlarged we can see that it is composed of both serous and mucous secretory units and therefore is a mixed gland, secreting water protein and mucus. The third area, the skin surface of the lip, when enlarged shows a keratinized epithelium, hair follicles and sebaceous glands. This is confirmed at this yet higher magnification.

precancerous colon polyp

A precancerous colon polyp is formed as a result of 'out of control' cell division of colon epithelial cells. The normal colon epithelium is indicated between the two dotted lines. In the precancerous polyp image the normal colon is also indicted between two dotted lines. The polyp formed by the proliferation of epithelial cells is located within the circle. You can see that the polyp is connected to the normal part of the colon by a stalk. This is what a physician is looking for when a colonoscopy is performed. If found during a colonoscopy, a wire loop is placed around the polyp and it is excised as a biopsy and submitted to a pathologist for examination. At this stage the polyp is a neoplastic growth. It is benign because it is still contained within the epithelial layer of the colon.

Villi and Intestinal Glands

A villus is a fold of the epithelium with the lamina propria as the core. The muscularis mucosa lies at the base of the villus. Villi project into the lumen and they are shaped like fingers. The villi in turn have a complex of capillaries (left drawing), a central lacteal (lymphatic capillary-middle drawing) & bands of smooth muscle (right drawing) that have contractile properties helping to keep nutrient molecules stirred up with the digestive enzymes between the villi by an alternating action of shortening and lengthening. A longitudinal section through a villus is shown on the right. The villus is covered with a simple columnar epithelium and the epithelium encloses the lamina propria as seen in the cross-section below. Villi are on the average 0.5 mm wide and range between 0.5 - 1.5 mm long. There are approximately 40 villi per square centimeter in the duodenum and jejunum and less in the ileum - about 10 villi per square centimeter. The intestinal glands are located between the villi. Intestinal glands are simple (no branching ducts) tubular (secretory cells arranged as a tube) glands.

Gomerulonephritis Acute post-streptococcal

Acute post-streptococcal glomerulonephritis is an infection of the glomerulus by streptococcal bacteria. A normal glomerulus is shown beside one with glomerulonephritis. Recall that bacteria attract neutrophils from the blood vessels. Several of many neutrophils are indicated by the arrows in the right image. Acute proliferative glomerulonephritis is a disorder of the glomeruli (glomerulonephritis), or small blood vessels in the kidneys. It is a common complication of infections, typically streptococcal skin infection (impetigo) and streptococcal pharyngitis, for which it is also known as post infectious or post streptococcal glomerulonephritis. The exact pathology remains unclear, but it is believed to be type III hypersensitivity reaction. Immune complexes (antigen-antibody complexes formed during an infection) become lodged in the glomerular basement membrane below the podocyte foot processes. This creates a lumpy bumpy appearance on light microscopy and subepithelial humps on electron microscopy. Complement activation leads to destruction of the basement membrane. It has also been proposed that specific antigens from certain nephrotoxic streptococcal infections have a high affinity for basement membrane proteins, giving rise to particularly severe, long lasting antibody response. This is an example of one of the complications that can occur as side effect of our body's immune response.

adenocarcinoma of the colon

Adenocarcinoma is a cancer the cells of which are derived from gland cells. In this case, the cells of the intestinal glands. The cancer term prefix is -adeno- because the cells were derived from gland cells and - carcinoma- because the cells were derived from epithelial gland cells. On the left is presented the normal epithelial lining of the colon where you can see many empty spaces that are actually single cells called goblet cells. On the right you see abnormal epithelial lining cells that no longer have empty spaces but are solid and are deeply stained. In the insets on the right and left, compare the normal epithelium on the left to the cancerous epithelium on the right. You can see in the adenocarincoma specimen that there are no goblet cells, the cells are darkly stained and the nuclei occupy more area in the cells. Finally, this cancer is malignant because the cancer cells have migrated through the basement membrane into the connective tissue as evidenced by the cells within the encircled region.

lung: visceral pleura

Air conducted down the trachea enters the right and left lungs via the primary bronchi (branches of the trachea). The entire lung is enclosed with a membrane consisting of a matt of connective tissue covered by simple squamous epithelium (mesothelium). Thiscombinationoftissues makes up the pleura, a serous membrane consisting of simple squamous epithelium (mesothelium), a basal lamina and loose connective tissue. The visceral pleura that covers the surface of the lung is seen here with a few alveoli at the edge of the lung. The visceral pleura reflects via the mediastinum to line the inside of the thoracic cavity. This is the parietal pleura. There is a small potential space between the two pleural membranes. The mesothelium of the parietal and visceral pleurae regulate the amount of fluid within the pleural space that exists between the lung pleura and the thoracic wall pleura so that the lung adheres to the thoracic wall because of capillary action. It is like two pieces of flat glass, like window glass, that are moist. They stick together whereas if they are dry then they do not stick together. In this way, when the thorax expands and the diaphragm lowers during inspiration the lung is pulled along thereby creating a negative pressure inside the lung so air rushes in through the airways to fill the lung.

intrapulmonary bronchus mucosa

All of the mucosa lining the bronchial tree (branches of the bronchi) has a rich population of lymphocytes. This is said to be the Bronchial Associated Lymphoid Tissue (BALT). The GI tract has a similar arrangement where it is termed Gut Associated Lymphoid Tissue or GALT. This provides a ready reserve of plasma cells and circulating T lymphocytes that guard the airway and react to airborne antigens.

View of right nasal cavity from nasal septum (fresh specimen)

As viewed from the nasal septum that divides the nasal cavity into right and left components. Observe the conchae, mucosal covered bony projections into the nasal cavity. Also observe the tongue, the opening of the Eustachian tube that leads to the middle ear, and the sphenoid sinus (one of several mucosal lined spaces that communicate by small ducts with the nasal cavity). The hard palate forms the floor of the nasal cavity. The entrance way into the nasal cavity is called the vestibule. It is lined with epidermis containing hair that participates in filtering the air breathed in. The respiratory region occupies most of the nasal cavity. The respiratory region is covered with pseudostratified ciliated columnar (PSCC) epithelium which is also known as Respiratory Epithelium. The olfactory region is located in the uppermost part of the nasal cavity. This relatively small area is where the specialized nerve cells are located that sense the molecules that produce an odor. In other words this is where our smell receptors are located.

villi and intestinal glands

Between villi the epithelium forms downward projected tubes that form simple tubular glands. These are the intestinal glands (also called the crypts of Lieberkuhn because they resemble a crypt and Dr. Lieberkuhn long ago discovered them). Paneth cells lie at the base of the gland. They are exocrine cells with prominent eosinophilic granules which contain lysozyme. Presumably this helps to keep the bacterial flora in check in the lumen. Regenerative or stem cells are also located in these simple tubular glands. They differentiate into all the other cell types, including the intestinal absorptive cell (simple columnar cells covering the villus that contain many microvilli). Enteroendocrine cells are present and they secrete a variety of peptides. Goblet cells are interspersed among the absorptive cells lining the villi. They appear in the duodenum & increase in number as you move along the GI tract. They secrete mucus that lubricates the lining of the GI tract. Absorptive cells (also called enterocytes) are tall columnar cells which have numerous microvilli (3,000/cell) on their luminal surface (striated border). Glucose, amino acids, lipids and other molecules resulting from digestion of food are taken into the body by these cells.

Bile Canaliculi: 3 views

Bile is collected from several adjacent hepatocytes into a very tiny channel called a bile canaliculus. This slide shows three different views of a bile canaliculus by three different methods. The first view is a histological section stained with H&E where a cross-section of a single bile canaliculus is indicated by the arrow. The canaliculus is bordered by three hepatocytes, one of which has two nuclei, a not uncommon finding in normal hepatocytes. Recall that the diameter of a canaliculus is on the order of 2 micrometers. The next view is the bile canaliculi in a whole mount of liver cells where the liver cells are yellow and the bile canaliculi are black due to a histochemical reaction for alkaline phosphatase, a chemical that resides within that part of the plasma membrane of the hepatocytes forming the canaliculi. The third view is as seen with the aid of an electron microscope. Observe the microvilli projecting into the lumen of the canaliculus. The heptocytes forming a canaliculus are joined together by tight junctions as illustrated in the higher magnification in the inset.

nephron segment functions

Blood is filtered across two cells (endothelial and epithelial) and a basement membrane. The ultrafiltrate of blood does not include any formed elements, just water, proteins less than 100,000 molecular weight, uric acid, urea, glucose, amino acids, and various electrolytes. As you can see, much of the filtrate is reabsorbed. The proximal tubule resorbs water, proteins, glucose and sodium. The descending side of the loop of Henle is permeable to water and salts so these go out of the tubule and urea enters the tubule. The ascending side of the loop of Henle is impermeable to water, but Na and Cl are transported to the interstitium making the interstitium very hypertonic. The distal tubule is impermeable to water and the hormone aldosterone transports sodium and chloride out of the urine. Finally, in the collecting duct the water content of urine is modified depending on the level of ADH. Now the details of the filtration apparatus in the renal corpuscle will be presented,

Nasal Cavity Blood Vessels Swell Bodies

Blood vessels are important components of the nasal mucosa. The key concept here is to understand what an arteriovenous (AV) anastomosis makes possible. When smooth muscle in an AV anastomosis is relaxed blood is shunted directly from the arteries into the veins and bypasses the capillary bed. If the muscle is constricted the blood is directed into the capillary bed and small venule. In the nasal cavity lamina propria there is a rich capillary and venule complex that, when engorged with blood, causes the tissue to swell thus increasing its size and projecting into the nasal cavity. This will decrease the area for flow of air and divert air from one nostril to another; a normal mechanism which gives alternate nasal cavities the chance to recover from drying out. The common cold results in the release of histamine by mast and other cells. This causes a dilation of arterioles, capillaries and venules, but a constriction of the muscle in AV anastomoses. This in turn causes swelling of the mucosa resulting in a 'stuffy nose'. Treatment with 'antihistaminic substances' relieves this condition.

glomerular filtration membrane

Both images were created with a Scanning Electron Microscope. The left image shows the cell body of a podocyte with its primary and smaller secondary (foot processes) enveloping the outside of a glomerular capillary. The right image is taken of the inside of a glomerular capillary and the edge showing the relationship between the podocyte and its foot processes (P) and the endothelial cell (E). The view is as if the specimen in the left image was cracked open in a plane parallel to the red dotted line. In the upper right part of the right image observe the tiny holes. These are the fenestrations (little windows or openings) in the endothelial cell (EF). The next slide will display a section through a glomerular capillary and podocyte as viewed in a transmission electron microscope.

the liver lobule

Central veins Located at center of each lobule Drain lobule sinusoids Central veins are drained by interlobular veins Liver Lobule 2 mm long x 700 microns wide 2 dimensional shape is a hexagon Composed of liver cells (hepatocytes) and sinusoids lobules are separated by connective tissue (stroma) Liver Triads lobule triad Hepatic artery, portal vein & bile duct Located around the peripheral aspect of each lobule This drawing illustrates three liver lobules, their blood supply & drainage, and drainage of bile via the bile ducts. A liver lobule, the repeating unit of organization of the liver parenchyma, is 3 dimensional. Its dimensions average 2 mm long and 700 microns (0.7 mm) wide. In 2 dimensions as viewed in a histological section, the lobules are hexagonal in shape. Each lobule is composed of liver cells that are termed hepatocytes and sinusoids. The lobules are surrounded and separated from each other by connective tissue (stroma) that is continuous with the capsule of the liver. At the peripheral aspect of each lobule are triads commonly located at the points of the hexagon. The hepatic artery and portal veins of the triad supply the sinusoids of each lobule with blood and the bile duct drains bile secreted by the liver's cells from each lobule. Central veins are located in the center of each lobule. The sinusoids in each lobule drain into the central vein. Blood is collected from the central veins of several lobules by an interlobular vein. In the lobule, blood flows from the peripheral aspect and bile secreted by hepatocytes flows in the opposite direction, toward the peripheral aspect or the portal areas.

Circumvallate Papilla & Von Ebners Glands

Circumvallate papillae receive secretions from serous glands nearby. The glands, von Ebner's glands, are made up of exclusively serous secretory units. Their secretions flush the moats surrounding the circumvallate papilla to enable the taste buds to respond to the changing stimuli during eating. This enlargement shows the serous cells and a duct that is connected to the epithelium at the base of the moat. Observe the histological features of the serous cells - round nuclei and basophilic cytoplasm.

clara cells

Clara cells are identified by the dome like shape of their apical surface. They do not have any cilia. Clara cells make up about 80% of the epithelial cells lining the terminal bronchioles. Clara cells contain enzymes and much smooth endoplasmic reticulum that can detoxify chemicals that are breathed from the environment. Clara cells also synthesize and secrete surfactant, a surface tension reducing substance that is also secreted by type II pneumocytes in the alveoli. More about surfactant later in this lecture.

Classic Lobule vs. Portal Lobule vs. Liver Acinus

Classic Lobule Axis center = central vein Blood collection PortalLobule Axis center = portal area Bile collection Liver Acinus Axis center portal area to portal area Blood supply Alternate terminology Hepatic artery alsointerlobularartery/arteriole Portal vein Also interlobular vein/venule Bile duct Also interlobular duct Central Vein alsoIntralobularvein/venule There are 3 distinct ways to view the microscopic architecture of the liver. The first is the classic liver lobule with the central vein at the central point of the lobule. The portal areas lie at the periphery of the lobule & provide circulation into the sinusoids by way of the hepatic artery (arteriole) & portal vein (venule). Bile drains towards the portal area into the bile duct (interlobular duct). In the portal lobule concept, the morphologic axis is the portal area, specifically the bile duct, because the most important exocrine function of the liver is the formation of bile. In the portal acinus concept, we combine circulation & bile formation together. The long axis of the acinus is from central vein to central vein while the short axis runs between the portal areas at the periphery of the classic lobule & on either side of the long axis. This creates a functional zonation of the cells which is reflected in their physiology & pathology. The wedge of tissue from the short axis to the central vein is arbitrarily divided into three equal areas called zones. Zone 1 is closest to the short axis, zone 3 is farthest from the axis & closest to the central vein. Zone 2 is less distinct & lies between 1 & 2. Cells in zone 1 are located nearest the lobule perimeter (the center of the liver acinus). The hepatocytes in this zone are the first to receive both nutrients & toxins. The blood they are exposed to has a higher concentration of oxygen than the hepatocytes in the other two zones. They are the last to die & first to regenerate. The cells in zone 3 received the blood with the lowest concentration of oxygen. The hepatocytes in this zone are the last to respond to toxins & bile stasis but the first to show fat accumulation. They are also the first to show ischemic necrosis (necrosis due to low oxygen) if there is a general state in the body of hypoxia.

esophageal cancer

Esophageal cancers are typically carcinomas which arise from the epithelium of the esophagus. Difficulty in swallowing is one of the symptoms of esophageal cancer. Most esophageal cancers fall into one of two classes: squamous cell carcinomas and adenocarcinomas. Squamous cell carcinomas are similar to head and neck cancer in their appearance are usually associated with tobacco and alcohol consumption. Adenocarcinomas are often associated with a history of gastroesophageal reflux. Gastroesophageal reflux is the backing up of acid from the stomach into the esophagus. Continuous reflux on a regular basis irritates the esophagus causing it to undergo first metaplasia to a columnar epithelial lining to dysplasia (abnormal pattern of cells) of the epithelium when it no longer resembles any normal epithelium to finally cancerous cells. This slide illustrates squamous cell carcinoma. Observe the normal on the left compared to the carcinoma on the right. This carcinoma has invaded the lamina propria with masses of abnormal squamous cells and therefore it is malignant. The enlargement of this boxed in region shows normal epithelium on the left and carcinoma of the epithelium on the right. This smaller boxed in area shows a close-up of a small amount of normal epithelium together with the carcinoma. Observe that the cancerous epithelium bears no resemblance to the normal epithelium.

facet cells of bladder epithelium

Facet cells are large cells composing the superficial layer of the transitional epithelium lining the bladder. They face the lumen and that is why they are called facet cells. The cell membranes bordering the lumen of these cells are thickened forming a face or facet. The term facet can mean the surface of an object as in the facets of a diamond, or, it can mean any definable aspect of a subject. These cells frequently have two nuclei (bi- nucleated) and the cells can be polyhedral (many sided) when the bladder is empty, or, when the bladder is full, these cells are stretchable so that they become flattened. So, the facets of the superficial cells are the thickened cell membranes. The vesicles are thickened cell membrane stored inside of the superficial transitional epithelial cells in an empty bladder when the epithelium is not stretched. When the bladder fills with urine the epithelium is stretched. The cells enlarge via the vesicles fusing with the cell membrane to provide more area for the stretching cells. Thus the bladder can expand greatly with the epithelium still intact.

normal v fatty liver

Fatty liver is a condition in which the hepatocytes become engorged with lipid even to the extent that they can resemble adipocytes. Observe in the normal liver the relatively even reddish-bluish staining of the H&E stained specimen. Compare this to the fatty liver specimen in which many light stained discrete areas are present. An enlarged view of both specimens clearly shows that fat has replaced most of the normal liver cytoplasm so that the liver is beginning to look like adipose tissue. When spread throughout the liver, the function of the liver is severely compromised. Fatty liver is associated with diabetes, hypertension and obesity. Chronic alcohol drinking is definitely a cause. A fatty liver can lead to cirrhosis, a severe scarring of the liver where most of the hepatocytes are replaced by scar tissue. This has at least two results: 1) liver function is compromised and 2) due to the fact that the scarring obliterates many of the sinusoids, the resistance of blood flow through the liver dramatically increases causing a condition known as ascites, the build up of fluid in the abdominal cavity.

stomach histology

Here we see a histological section at low magnificationofthewallofthestomach. Notethe mucosa, muscularis mucosa - one of the components of the mucosa, the submucosa where you can observe loose connective tissue, adipose tissue, but no glands and the muscularis externa, that unlike the esophagus, it is organized in 3 layers. The outer layer is longitudinal, the middle layer is circular and the internal layer is oblique. At the pylorus, the middle layer is greatly thickened to form the pyloric sphincter.

Important Concept Mucosal Vs. Submucosal Gland

First, an important concept. All glands are composed of epithelial cells, specifically, glandular epithelial cells. Glands may be one cell or multicellular. Salivary glands are complex multicellular glands organized with a series of ducts and secretory acini. In the remainder of the GI tract we will encounter glands that are just merely tubes, or glands that have one or two ducts that branch at the end of which is a collection of secretory cells (e.g. mucous cells). A very important component of the esophagus, stomach and intestines are glands that reside within the wall of these segments of the gastrointestinal tract. The glands are located in either the mucosa or the submucosa or both. A mucosal gland is always located within the mucosa and is a part of the epithelial lining. Recall that the mucosa consists of the epithelial lining, the lamina propria (loose connective tissue) and the muscularis mucosa. Illustrated here in the left image are mucosal glands that are tubes. The secretory cells make up the wall of the tube and the product moves through the tube lumen to the lumen of the GI tract. The specimen on the left is from the colon. Observe the muscularis mucosa noting that the simple tubular glands are located in the epithelial layer surrounded by the lamina propria. The glandular cells here are goblet cells. The specimen on the right illustrates the submucosal gland. A submucosal gland is located in the submucosa and therefore by definition is not a part of the mucosa as it is located beneath or external to the muscularis mucosa. Observe the muscularis mucosa noting that the gland is located beneath or external to the muscularis mucosa. Although not shown in this specimen as the plane of section did not pass through it, all submucosal glands are connected to the lumen by a duct. Submucosal glands are found only in the esophagus and duodenum (first part of the small intestine). As you learn the histology of the GI tract stay alert as to whether the glands are mucosal or submucosal in the particular segment you are studying.

cystic fibrosis

For the escalator to run smoothly there has to be an optimal viscosity of the mucus determined by water concentration. Water is controlled by the amount of salt, the secretion of which by the ciliated epithelial cells is controlled by a certain transporter protein which is formed by the expression of a gene for a Transmembrane Conductance Regulator Protein. Defect in this gene is the cause of CYSTIC FIBROSIS Cystic Fibrosis is a genetic disease that results in the mucus of the respiratory tract being too stiff and therefore mucus tends to clog the airways interfering with easy flow of air. It only takes a slight alteration in the concentration of chloride in the lumen of the trachea and bronchi to disturb the viscosity of the mucus layer. If the concentration of chloride ions falls below normal, then less water is secreted into the lumen resulting in the mucus being so thick that the cilia cannot move it. Therefore the lumens become congested with mucus. This all happens because of the failure of a gene to express the correct instructions to a membrane protein.

accessory glands

Form from diverticuli of the digestive tube As we take our journey through the GI tract we will encounter glands that are connected by a duct whose lumen is continuous with the lumen of the GI tract. Although the gall bladder is not a gland, per se, it is in the sense that it does process the bile salts that it receives from the liver and therefore can be thought of as a gland because it delivers a different product to the GI tract then it receives from the liver. During embryonic development each of the glands is formed by out-pocketing of the epithelial lining of the embryonic GI tract accompanied by embryonic connective tissue. It is the proliferation of these tissues that form, for example the hepatocytes of the liver and all accompanying tissue to form the adult liver. The liver, gallbladder and pancreas will be presented in a separate lecture.

goblet cell

Goblet cells are interposed between the absorptive cells covering the villi. They synthesize and release mucus in cycles. They increase in density from the duodenum to the colon where they are dominant in the epithelium of the colon intestinal glands with only a few absorptive cells bordering the lumen. Mucus or mucins are a family of high molecular weight, heavily glycosylated proteins. Goblet cells store mucus until the cell is greatly distended so that the dimension of the cell above the nucleus is wider than the width at the nucleus and below. When the goblet cell is full of mucus it is shaped like a 'goblet' hence the name. Unlike stomach surface lining cells that also produce mucus, but continuously, goblet cells expel their gorge of mucins all at once. In the drawing note the mucus plug. At some point this plug is lost and the mucus just pours out onto the epithelial surface.

pancreas

Grossly the pancreas has a head and a tail. The head is the larger portion and it lies in the C-shaped curve of the duodenum. The pancreas is a mixed gland exhibiting both endocrine & exocrine functions. It is a histology look alike for parotid gland but can be distinguished based on 2 characteristics: no striated ducts in the pancreas but there are in the parotid & the endocrine function is delineated by the islets of Langerhans which are found only in the pancreas, not in parotid. The beginning of its duct system in the pancreas, the intercalated duct, is actually enveloped by the acinar cells not attached to the end of the acinus as in the parotid. Therefore in cross-sections of the acini in the pancreas a duct cell is often present and this is called the 'centroacinar' cell, a unique histological feature of the pancreas.

alveolar capillaries

Here are two views of capillary density and pattern in the alveolar septae of alveoli. The left image shows several alveoli and the right image shows one alveolus. The preparation was made by injecting the capillaries with a red plastic and then removing all of the tissue so that a cast of the capillaries remains. Blood flows across each alveolus through the capillaries as if the blood were a moving sheet of flow.

palate

Here we can see more detail of the roof of the oral cavity. The anterior most part of the hard palate epithelium is firmly bound to the underlying bone with no intervening tissue except for connective tissue, whereas the posterior aspect and continuing into the soft palate we see first a yellowish caste to the surface because adipose tissue constitutes a significant part of the tissue intervening between the epithelium and bone, after which we see an area of more pinkish caste to the epithelium with tiny red spots, the opening of the palatine glands (example of minor salivary glands).

colon histology detail

Here we see the many goblet cells in the intestinal glands of the colon mucosa and the surface cells that are absorptive. The detail of the submucosa reveals loose connective tissue, adipose tissue, blood vessels and a lymphatic nodule with a germinal center. The muscularis externa consists of an inner layer of smooth muscle that is oriented circularly and an outer layer of longitudinally oriented smooth muscle. An enlargement of the muscularis externa and the serosa reveals their detail. In this specimen the inner circular layer smooth muscle cells are sectioned in a plane parallel to their longitudinal axis as verified by this enlargement. Observe the myenteric plexus of Auerbach consisting of autonomic nerve cell bodies and processes between the inner and outer muscle layers. The outer longitudinal layer of smooth muscle cells are sectioned at right angles to their longitudinal axis (cross-sectioned). From this information you can determine whether this specimen, when prepared for microscopy, is a longitudinal or cross-section. So, which is it? It is a cross-section because the outer longitudinal oriented layer of the muscularis shows cross- sectional profiles of the smooth muscle cells. This can be determined for any segment of the small and large intestines. When a pathologist is cutting in a specimen to be examined the usual procedure is to cut a length of the intestine and then section it longitudinally because that provides more of a sample for inspection in the microscope. If this were that kind of section, the outer muscle cells would show longitudinal profiles.

Respiratory Mucosa: Respiratory Epithelium and Loose Connective Tissue

Illustrated in this slide is a short stretch of respiratory tract mucosa much as you would see it whether you encountered it lining the respiratory region of the nasal cavity, the trachea, bronchi or the larger bronchioles. It is composed of the Pseudostratified Ciliated Columnar Epithelium and loose connective tissue, otherwise known as the Lamina Propria. Ciliated cells, in addition to providing the force of moving cilia, also transport chloride ions from the underlying tissue to the lumen and this provides a flow of water into the lumen. There is an enormous population of cilia. Assuming 300 cilia per cell and an area of the end of each cell of 100 square micrometers. An extrapolation to the number of cilia per square mm (1,000,000 square micrometers /100 X 300) would estimate on the order of 3 million cilia per square mm, or up to 1 billion cilia/ square centimeter. This inset of a scanning electron micrograph viewing the epithelium from above shows goblet cells and the cilia of ciliated cells. If you think of the cilia as blades of grass covering a lawn, the cilia lining the conducting airways is very dense forms a very dense carpet of motile 'grass'. Goblet cells provide the mucus and stem cells near the basal lamina provide cells for renewal of the epithelium. Note the dividing cells in the population of basal cells of the epithelium on the right side of this image.

Review of Histology of Principal cells of the Fundic Gland Chief Cells (C), Parietal Cells (P) and Mucous cells (M)

In comparison to the highly eosinophilic (acidophilic) profile of the parietal cells (P) and the lightly stained mucous cells (M) that show rounded profiles containing the mucus, the chief cells (C) are deeply basophilic (cells with boundaries delineated by yellow lines) confirming the presence of large amounts of RER for protein synthesis. Chief cells synthesize and secrete pepsinogen into the lumen of the stomach. The action of hydrochloric acid produced by parietal cells converts pepsinogen (a pro-enzyme) to pepsin (the active enzyme) that hydrolyzes proteins into small peptides.

esophageal lining mucosa

In the right image we see how the esophagus looks if it is opened at an autopsy. The mucosa is white opaque because there are so many layers of epithelial cells in the stratified squamous non- keratinized epithelium that there is no possibility for the color of blood to be reflected. The left image is a histological specimen of the esophageal mucosa and submucosa. Observe the very thick epithelium that consists of nearly 40 layers of cells. Observe the muscularis mucosa composed of bundles of smooth muscle cells between the dotted lines. In the submucosa are two clumps of mucous type glands indicated by the arrows.

kidney blood vessels

In this drawing illustrating the blood vessels that supply and drain the kidney we shall follow the path of blood flow. Blood enters the kidney via the renal artery then flows into the interlobar arteries into the arcuate arteries that arch between the cortex and medulla. Smaller arteries, the interlobular arteries, branch at right angles from the arcuate arteries going straight into the cortex. Companion interlobular veins drain the cortex into the arcuate veins, then blood is collected in each inter lobar vein and finally blood flows out of the kidney through the renal vein. If we look closer at this rectangular area of a section of the cortex and medulla we see the details of the blood supply to one nephron (colored green) and a collecting duct (colored yellow). The nephron begins at the Renal Corpuscle (Bowman's capsule and a glomerulus). A nephron is composed first of a convoluted tubule, next the loop of Henle then, the distal convoluted tubule ending with a connection to a connecting tubule that then joins a collecting duct (yellow). Now observe the arcuate artery and vein gives rise and drains the interlobular artery and vein, respectively. The interlobular arteries and veins are always located between kidney lobules (lobules are subsections of the kidney lobes - more about that later). The capillaries in the glomerulus are supplied with blood from the afferent arteriole and drained of blood by the efferent arteriole. (This is a unique arrangement because the capillaries are supplied and drained of blood by arterioles). Finally, observe that there are two medullary capillary plexi, one in the interstitium between the tubules and the other surrounding the loop of Henle (LH). The interstitial capillary plexi are fed by a branch of the afferent arteriole and drain via a tributary into the arcuate vein. The cortical and medullary tubule plexi are fed by the efferent arterioles and drain via a tributary into the arcuate veins. As we will see in the next two slides, the interlobular arteries course between kidney lobules.

parotid duct

Note the gross anatomical location of the parotid gland and the excretory duct leading from it overlying the buccinator muscle and just inferior to the ear. Here we see in the photograph the site where the duct from the parotid gland (Wharton's duct) empties into the buccal aspect of the oral vestibule at the level of the 2nd molar tooth.

kidney lobules

In this low power view of the kidney cortex two lobules are shown. A lobule consists of all of the nephrons that connect and empty their product and contents into a collecting duct. The collecting ducts are located in regions running at right angles to the surface of the cortex. The loops of Henle components of the nephrons are located in this same region and the region is called a medullary ray. Note the location of the medullary rays in this image. When a portion of a medullary ray is enlarged one can see the longitudinal profiles of collecting ducts and the straight portions of the descending and ascending loops of Henle with a glomerulus and the convoluted portions of the nephron tubules on either side. The medullary ray is the center of a lobule. The convoluted tubules and glomeruli reside in the regions on either side and this is known as the cortical labyrinth (CL). The border between two kidney lobules is formed by an interlobular artery the branches of which are afferent arterioles supplying the glomeruli of the lobule located in the cortical labyrinth. Observe the example outlined in the low magnification and how the interlobular artery and one of its branches appears in the enlargement. In the next few slides the detailed histology of each segment of a nephron will be presented.

lungs in the thoracic cavity

It is helpful to know where the lungs are placed in the thoracic cavity with reference to the surface of the chest, side and back of the thorax. A frontal view shows the right lung with 3 lobes and the left lung with 2 lobes. Observe the position of the heart anatomically in the thorax. A back view shows the extent of right and left lungs. The upper lobe apexes extend just under the shoulders. A side view shows the apex of the upper lobe of the lung to be located just inside the arm pit. Right and left lungs are essentially for extreme activity and leading a good quality of life. However, life can be sustained with only one half of one lung.

mucous and serous membranes

It is important that you understand the difference between a serosa and a mucosa before we proceed with the histology of the respiratory organs as you will encounter both during this lecture. Serous membranes line closed body cavities such as the peritoneal cavity while mucous membranes line cavities that connect to the outside of the body such as the alimentary canal. This slide illustrates the components of both contrasting their structure. When the histology of the cardiovascular organs was presented, the lining of the blood vessels, simple squamous epithelium, was termed endothelium. Body cavities such as the thoracic cavity that holds the lungs and heart are lined with simple squamous epithelium on a bed of loose connective tissue. The simple squamous epithelium is termed mesothelium and the combination of the mesothelium and the loose connective tissue constitutes what is called a serosa or also referred to as a serous membrane. Serous membranes border cavities containing a small amount of fluid. Thus whether it is the thoracic cavity or abdominal cavity the cavity is lined with this serous membrane and the organs contained in the cavity are covered with the membrane. Around or surrounding the lung the membrane is known as parietal or visceral pleura. Parietal lining the cavity wall and pleura covering the lung. In contrast to the serosa is a mucosa or also referred to as the mucous membrane. A mucosa is composed of different kinds of epithelia depending on its location. A mucosa or mucous membrane lines the gastrointestinal tract fromtheoralcavitytotheanus. Mucous membranes line the trachea and major airways of the lung. Mucous membranes also line other hollow organs like the urinary bladder, the uterus, etc. These mucous membranes will be presented in detail as we study the various hollow organs. Note that the use of the term membrane is to denote the combination of epithelium and loose connective tissue with an intervening basal lamina that forms a barrier to separate one compartment from another. Note the distinction between 'mucus' a noun denoting a product of a cell and 'mucous' an adjective denoting a cell or structure related to mucus.

Alveolar Space Moisture Maintenance

It is very important that the alveolar spaces be maintained relatively dry and lined mostly by surfactant. Maintaining a relative dry alveolar space is accomplished by tight junctions of the arterioles and capillaries and osmotic pressure of the interstitium to retrieve any excess fluid that escapes. Note the presence of lymphatic capillaries. These lymphatic capillaries function like a sump pump. They receive and carry away any filtrate from the blood that is not picked up by the venules. This normal structure and physiology can be upset by infection by bacteria or viruses which lead to fluid in the alveolar spaces as will be illustrated in the next slide showing a histological specimen of a normal lung contrasted to a specimen taken from a lung of a patient with pneumonia.

smoking and metaplasia of respiratory epithelium

Metaplasia literally means a change in morphology (form). Histologically it is a change in one normal fully differentiated cell type or, in this case, an epithelial tissue to another normal fully differentiated cell type or tissue that is not normally found in that location. It occurs in the body when cells or tissues are subjected to physiological or pathological stresses. The most common metaplastic change is from the respiratory type with cilia and goblet cells as illustrated here, into, after many years of chronic smoking, into a stratified squamous non- keratinizing epithelium that is not normally found lining the trachea or bronchi. When a person starts smoking for the first time, the earliest change is loss of normal function of the cilia. They become disoriented and uncoordinated so that mucus is not moved effectively. Next the cilia are lost. Finally there are no cilia and no goblet cells. Therefore, the mucociliary escalator has not any longer a normal structure and the function is lost. The earliest symptom is a mild cough that eventually develops into a chronic heavy coughing in an effort to move substance from the lung to the oral pharynx. Without cilia the mucus goes the way of gravity -down into the air passages of the lungs. Even patches of metaplastic epithelial change will disrupt the escalator so that neighboring normal epithelium may have cilia and goblet cells producing mucus, but the mucus will be stopped over the metaplastic epithelium. The normal mechanism cannot any longer work and therefore, deep lung congestion occurs and bacteria, dust and other substances collect to cause infection. In extreme cases where the condition is complicated by emphysema (also known to be associated with smoking) the patient nearly has to stand on his or her head to expectorate anything from the lungs. A metaplastic change does not usually lead to cancer. However, prolonged exposure to a stress as 'smoking cigarettes' can lead to cancer of the lung airways. A common cancer in this case is bronchogenic carcinoma. The cancer arises in the respiratory epithelium lining a bronchus

distribution of taste sensation

Molecules in the food we eat and fluids we drink find access to the taste pore and then interact with the cells inside the taste bud. Sensory nerves synapse with the base of the neuroepithelial cells and carry the taste signal to the brain. The neuroepithelial cells react to five basic stimuli: sweet, salty, bitter, sour, and umami. "Umami"representsthetasteofcertain amino acids (e.g. glutamate, aspartate, and related compounds). It is common to asparagus, tomatoes, cheese and meat. The amino acid L- glutamate is mainly responsible for the umami taste. A gene that encodes for the glutamate receptor has been identified. Monosodium glutamate, added to many foods to enhance their taste (it is the main ingredient of soy sauce), stimulates the umami receptors. Bitter taste sensation is pretty much restricted to the root of the tongue so that taste buds in the circumvallate papilla account for this sensation. Sour is relegated to the sides of the tongue so that taste buds in foliate and fungiform papillae account for this taste sensation. Sweet and salty sensations are located at the tip of the tongue so that taste buds in fungiform papilla would be responsible for this sensation.

peristalsis

Nerves from Auerbach's plexus stimulate smooth muscle of muscularis externa causing a Peristalsis is a radially symmetrical contraction of muscles which propagates in a wave down the muscular tube to propel the contents of the intestinaltracttowardtheanus. Theplexiofnerve fibers that extend from cells bodies of parasympathetic neurons in ganglia located in Auerbach's myenteric plexus innervate the smooth muscle of the muscularis externa. The rhythmic stimulation by these nerves causes the coordinated wave-like contracting and relaxing that propels digesting food and the feces in the colon. One developmental abnormality results in the absence of the neurons and their processes of the myenteric plexus in the colon. This leads to the disease known as Hirschsprung's disease. Hirschsprung disease is a disease of the large intestine that causes severe constipation or intestinal obstruction. Constipation means stool moves through the intestines slower than usual. Bowel movements occur less often than normal and stools are difficult to pass. Some children with HD can't pass stool at all, which can result in the complete blockage of the intestines, a condition called intestinal obstruction. People with HD are born with it and are usually diagnosed when they are infants. Less severe cases are sometimes diagnosed when a child is older. An HD diagnosis in an adult is rare.

lip landmarks

Normally the external surface of the lips is red because of the proximity of the blood vessels in the connective tissue beneath the epithelium. The epithelium starts out in the young as nonkeratinized or slightly keratinized, allowing for the color of blood to be seen. Application of lipstick is guided by the sharp border between the outer edge of the lips and the skin. At that point the epithelium changes from non- keratinized to the typical keratinized epithelium of the epidermis of the skin. The border between the red area of the lip and the skin is called the vermilion border. Lips are the entrance to the oral cavity & present differently based on dentition, age, exposure to weather, skin color & general health.

parietal cell function

Observe this drawing of a parietal cell noting the intracellular canaliculus, the carbonic anhydrase enzyme that facilitates combining of water and carbon dioxide, the active transport of hydrogen and chloride ion and the many mitochondria. To make hydrochloric acid, the parietal cell ribosomes synthesize an enzyme called carbonic anhydrase. Carbonic anhydrase facilitates the combination of carbon dioxide & water to make carbonic acid, a highly unstable molecule which breaks down almost immediately into the hydrogen ion & the bicarbonate ion. The H+ is actively transported across the membrane in the numerous intracellular canaliculi present in the parietal cell. An intracellular canaliculus is a deep invagination of the cell membrane with folds that greatly increase the surface area of the plasma membrane. In this membrane there are proteins that literally and actively pump or carry hydrogen ions from the cytoplasm into the lumen of the fundic gland. There, hydrogen ions complex with chloride ions to make hydrochloric acid. The chloride ions, as the drawing indicates, are actively transported from the interstitium on the capillary side of the parietal cell, across the parietal cell, again by a membrane protein pump into the lumen of the fundic gland. The bicarbonate ion diffuses into the interstitium and is picked up by blood capillaries. The two pumps require energy to function and that energy is supplied by the many mitochondria present in a parietal cell. The more hydrochloric acid is produced the more bicarbonate is formed. The result is acid for digestion and the alkaline bicarbonate for buffering against the acid digestion of the lumen lining epithelial cells as we shall see in the next slide.

Renal Corpuscle: LM & SEM Views

On the left is a medium high magnification view of the cortex of a kidney stained with H & E. The renal corpuscle is seen in the center with its vascular pole and urinary space (US). Below the corpuscle an example of a proximal convoluted tubule and a distal convoluted tubule are labeled. Observe the erythrocytes in the capillaries of the glomerulus. The image on the right is a scanning electron micrograph of a renal corpuscle with part of Bowman's capsule removed. The structures that look like worms are capillaries. At several loci along the capillaries you can see swellings, some of which are labeled Po. These are the cell bodies of the cells that make up the visceral layer of Bowman's capsule and they are called Podocytes. This term denotes the fact that these cells have processes that look like feet that end upon and enclose the endothelium of the capillaries. The filtration membrane of the kidney glomerulus involves the capillary endothelium, an intervening basement membrane and the podocyte. We shall now look into the relationship between these 3 structures and how they form the filtration membrane.

ileum peyers patches

Peyer's patches of the ileum Composed of lymphatic nodules in large groups Found in the lamina propria and submucosa Provide Secretoty IgA to the lumen Special openings in the intestinal epithelial basal lamina Antigen is exposed to antigen presenting M cells in the epithelium Antigen is presented to CD4+ T lymphocytes in the lymphatic nodules Programmed T cell can then activate B cells that become plasma cells that secrete the secretory IgA. Peyer's patches are unique to the ileum. They are large groups / masses of lymphatic nodules that occupy the mucosa and submucosa in the wall of the ileum opposite the attachment of its mesentery. Special cells in the epithelial lining call M cells overlie the Peyer's patches. They have microfolds at their apical surface rather than microvilli. They take up microorganisms and macromolecules from the lumen in endocytotic vesicles. The M cell is an antigen presenting cell. The antigen is presented to T cells that activate B cells that are cloned in the lymphatic nodules. B cells transform into plasma cells, which secrete secretory IgA that passes into the lumen of the intestine to interact with the antigen. This is similar to the role that plasma cells play in the salivary glands.

pnuemonia

Pneumonia, whether caused by bacteria or viruses, results in protein rich fluid moving into the alveolar spaces which significantly interferes with normal gas exchange because the surface area available is greatly reduced. Protein, fluid and cells have escaped from the blood into the alveolar spaces because tight junctions in the endothelium of capillaries and the alveolar type I and II cells failed. Note also that erythrocytes fill capillaries - evidence of congestion. In this particular case this is an exudate. An exudate is edema fluid with a high protein concentration that includes blood cells. If the fluid lacked cells and had a low protein concentration it would be a transudate. Compare the lower image of a specimen showing early pneumonia with the upper image of a normal specimen.

histology of lips

S l i d e 1 2 Lips have three surfaces - 1) the skin surface, 2) the oral vestibule surface and 3) the transitional surface (red area). The skin side is typical epidermis and dermis histology. The vestibule side is moist and lined with stratified squamous non-keratinizing epithelium. The moist red area that is covered with the same type of epithelium unless weather beaten or aged as we saw in the last slide in which case the epithelium would be keratinzed. Observe the location of the minor salivary glands in the submucosa layer of the lip. They are called labial glands. These are mixed glands, i.e. they are made up of both serous and mucous acini. There are many with openings into the vestibule for each gland. Minor salivary glands are located in the submucosa throughout the oral vestibule and oral cavity. You can actually feel the minor salivary glands with your tongue by moving the tongue along the lip side of the oral vestibule. They feel like small bumps. If one ever gets infected or the duct is blocked then the bump will be large and tender. In the central or core of the lip is the orbiculis oris muscle, a striated muscle that is one of the many muscles of the face. It is responsible for lip movement. Observe the location of the gingiva (the gum) surrounding the tooth. The gingival epithelium is partially keratinized (parakeratinized) and the epithelium firmly attaches to the tooth so that, normally, no food, bacteria or any substance can enter the connective tissue by passing between the tooth and the gingiva. The tooth itself is composed of dentin covered by enamel. The next slide will illustrate further the histology of the lips.

tooth histology

S l i d e 1 9 This is a drawing of a tooth in situ in its normal setting surrounded by bone. The visible part of the tooth in the oral cavity is covered with enamel and this is termed the crown of the tooth. The remainder of the tooth is not visible. The gingiva covers the neck of the tooth which is where the enamel and dentin meet. Below that the remainder of the tooth is the root and it is attached via a very short but strong ligament to the surrounding bone. Underlying the enamel is the dentin that not only is the substance under the crown region by makes up the bulk of the tissue of the root. Enamel is very hard. Its composition is 98% mineral and acellular (lacks any cells). It is vulnerable to acids and cannot repair itself. In the core of the tooth all surrounded by dentin is the dental pulp. It is a primitive type of connective tissue with blood vessels, nerves and special cells that formed the dentin. These cells are called odontoblasts and they still exist in an adult tooth. Odontoblasts arise in the developing tooth in the dental papilla, a primitive connective tissue. Odontoblasts develop from mesenchymal cells. They grow and develop long processes that reach over one half the way to the outer surface of the dentin. Dentin, if damaged can sort of repair itself. Odontoblasts can secrete dentin at the interface between dentin and the dental pulp. Dentin is not nearly as hard as enamel. It is composed of 80% mineral and 20% organic most of which is collagen. Surrounding the dentin is a bone like material, the cementum. Cementum is fastened tightly to the dentin. Outside of the cementum on all sides of the tooth is bone. It is called alveloar bone. Between the bone and the cementum is the periodontal ligament composed of blood vessels, nerves and dense collagen fibers. The collagen fibers are anchored in both the bone and the cementum covering the root. This is a very strong ligament that is broken by the dentist when a tooth is extracted.

Tongue Papilla: filiform & fungiform

S l i d e 2 5 The dorsal or upper surface of the tongue is covered with stratified squamous epithelium with a variable degree of keratinization. The papillae of the tongue as a rule are more keratinized than adjacent areas. Most of the papillae covering the anterior 2/3 or body of the tongue is of the filiform type. They look like filaments projecting from the surface. The projections have a lamina propria (loose connective tissue) core and they are covered with keratinized stratified squamous epithelium. Filiform papillae are very numerous. They provide the tongue with the ability to lick the ice cream off of an ice cream cone. Without these papillae ice cream retrieved by licking would not be possible because the tongue would be so smooth that it would just slide over the ice cream. This occurs in aged persons. Filiform papillae gradually atrophy. In cats these papillae are highly developed. They are very rigid and conical in shape. In fact they resemble the teeth of a comb. That is why cats can comb their hair. The fungiform papilla are less numerous. Observe four that are encircled on this specimen of a human tongue. They appear reddish or pink. A section through them as seen in the drawing shows that they are shaped like a fungus with a flattened surface projecting just slightly above the surface of the tongue. The epithelium is relatively less keratinized than that of the filiform papilla. They may have taste buds within the epithelium covering their surface.

major salivary glands

S l i d e 2 9 The parotid, submandibular & sublingual & their associated ducts are considered to be the major salivary glands. The parotid gland is located beneath the skin and occupies an area in front of and below the ear. Its duct passes through the cheek muscle and mucosa and empties its secretions into the oral vestibule at the level of the upper 2nd molar tooth. The submandibular gland is located beneath the skin under the mandible and its duct passes through the muscles and mucosa of the floor of the oral cavity and empties its secretions through a duct that opens in the lower aspect of the tongue. The sublingual gland is located between the muscle of the floor of the mouth and the mucosa. It is essentially located within the floor of the oral cavity. It has multiple ducts that empty into the oral cavity along the lower surface of the tongue.

Submandibular & Sublingual Duct Openings

S l i d e 3 1 S l i d e 3 2 This is a view of the underside of the tongue. Observe the lingual frenulum in the midline. The frenulum attaches the tongue to the floor of the oral cavity. The bluish areas on either side of the frenulum reflect the underlying presence of the veins that drain the tongue, the lingual veins. The main excretory ducts of the right and left submandibular glands open beneath the tongue in paired openings on either side of the root of the frenulum as encircled. The locations are circled but the openings are not clearly visible in this specimen. The right and left sublingual glands are located beneath the mucosa and above the muscle that forms the floor of the mouth. They have multiple excretory ducts that penetrate the mucosa and open in the regions indicated by the oval shapes along both sides of the midline beneath the tongue.

salivary gland

S l i d e 3 3 This slide illustrates the components of a salivary gland. Each acinus contains multiple cells of either the mucous or serous type. In some cases a single acinus may contain a core of mucous cells and a cap of serous cells as you can see in this drawing. This is called a serous demilune (a half moon shape of serous cells capping a collection of mucous cells). The acinar cells empty their secretions into a central lumen that is continuous with a series of ducts that begin small and gradually get larger. The smallest duct is the intercalated duct. Its wall is made up of a simple cuboidal epithelium. Next, is a striated duct made up of simple columnar epithelium. Specialized cells that act as muscle cells surround the acini and the smaller ducts. These are myoepithelial cells that contract to move secretions from acini into and along the ducts. All of these components are not present in each of the major salivary glands. For example, in the case of the parotid gland all of the acini are composed of serous cells. In the submandibular gland there is mix of serous and mucous acini but the serous acini are dominant. The sublingual gland has a mix of serous and mucous acini but the mucous acini are dominant. The submandibular and sublingual glands contain serous demilunes, but the parotid gland has no serous demilunes.

comparing major glands

S l i d e 3 5 In this slide we will compare and contrast the histology of the major salivary glands at the secretory level. The parotid gland only has serous acini. It secretes mainly an enzyme that breaks down glycogen (salivary amylase). The parotid gland has many striated ducts because the parotid gland contributes most of the salivary gland fluid. The tonicity and pH of the saliva is controlled by the secretions and reabsorption of ions by the striated ducts. The submanbibular gland is a mixed gland having both mucous and serous acini, but the dominate acinus is the serous acinus. The sublingual gland is composed of mostly mucous acini. Both the submandibular and sublingual glands also have the unique acini that are a mixture of mucous and serous cells. The serous cells cap the mucous cells in those acini. That arrangement is called a serous demilune.

type 1 and 2 alveolar cells

SEM of alveolar wall air surface illustrating type I and type II cells. Note the small projections from the surface of the type II pneumocyte (alveolar) cell. Note, in contrast, the very smooth surface of the type II (alveolar) pneumocyte.

oral mucoosa

So, now, here is our first look at the histology of the GI tract, the oral mucosa. The floor of the mouth, buccal region and soft palate are bordered by 'lining mucosa' where the stratified epithelium is not keratinized at all. The hard palate and gingiva are covered with 'masticatory mucosa' where the epithelium is partially keratinized (the several layers of cells near the surface contain both keratin and nuclei). Masticatory Mucosa is present where food mostly commonly collides during mastication (the act of chewing). Lining mucosa is present in all other areas where food is encountered but not in the force it is in the masticatory surfaces. The larger area of the oral cavity is lined by stratified squamous non- keratinizing epithelium that receives on its surface the secretion of the many minor salivary glands distributed throughout connective tissue beneath its epithelial lining. This secretion is contains mucus and water so that the lining is wet and somewhat slippery. Note at the surface of this lining the cell at the left side that appears to be in the process of separating from the lining. This is a squamous epithelial cell that is undergoing a process called desquamation...........i.e. it is being shed or sloughed off. This is very common, occurring everyday as the oral epithelium is continuously renewed by division of cells in the basal region of this epithelium. The rate of renewal is every 3 - 4 days. That is, your oral epithelial lining is made up of totally different cells in this time frame. That is why a cut heals very quickly in the mouth. The other epithelium of partially keratinized and lines the hard palate and the gingiva. This design meets the abrasion that occurs during mastication where food is pressed against the hard palate by the tongue and cascades alongside the teeth where it constantly rubs against the soft tissue surrounding the tooth, the gingiva. One can always expect that an epithelium will accommodate to abrasion by either being keratinized or partially keratinized in the first place, or, if non-keratinized and subjected to abrasion over time will respond by becoming keratinized to the degree of abrasion and dryness.

kidney lobe contents

Stepping back from the detail, it should be helpful to study this slide where you have a low magnification view of a histological section through a kidney lobe on the left and a drawing showing the placement of the nephrons + collecting ducts = uriniferous tubules. Recall that the renal corpuscles with glomeruli are only located in the cortex. Note that that there are nephrons with long and short loops off Henle. Observe also that some nephrons begin close to the capsule, others in the middle of the cortex and still others near the junction of the cortex with the medulla. The so-called juxta- medullary nephrons have the longest the loops and they are the ones that contribute most to making the urine hypertonic thus conserving water under the influence of antidiuretic hormone (ADH). The outer stripe contains the thick ascending and descending segments of the loops of Henle, the inner stripe contains a mixture of thick descending and thin segments of the loops, and the inner zone is composed of only collecting ducts and thin segments of the loops of Henle. Observe how the medullary rays are the straight tubules in the cortex, ascending and descending thick segments of the loop of Henle, and along with the collecting ducts in the cortex form profiles that are relatively parallel. The medullary rays are the center of the kidney lobules, the sub-components of the kidney lobes. Think of the tubules in the medullary rays as the stems of a bouquet of flowers and the convoluted tubules the connecting stems to the flowers which are the glomeruli. One half way between each medullary ray in the cortex is the boundary between two lobules and that is the location of the interlobular artery and vein.

Surfactant keeps alveoli open

Surfactant, as you know now, coats all alveoli. Surfactant is a phospholipid synthesized and secreted into the alveolar spaces by type II pneumocytes. The normal thickness of surfactant coating the alveoli prevents alveoli from collapsing when we breathe out (expiration). As the diameter of the alveolar spaces decrease during expiration the layer of surfactant becomes thicker and the surface tension decreases countering the collapse of the alveoli. When not enough surfactant is present, as is the case in premature babies born before 27 weeks in utero, the alveoli collapse which results in difficulty in breathing and exchanging gas. This is known as Respiratory Distress Syndrome (RDS). When alveoli are expanded as in inspiration, the surface tension of the alveolar space surface increases due to the thinning of the surfactant.

alveolar septum

The alveolar wall and all of its components are illustrated in this slide. The alveolar wall or alveolar septum separates two alveolar spaces. Within the septum are capillaries lined with non- fenestrated endothelium. These account for 30% of septa cells. Covering the septum are type I cells that are very flat and thin accounting for 8% of the cells but contributing most of the surface area of the alveolus. The other cell type lining the alveolus is the type II pneumocyte. A fused basal laminae of the endothelial cell and the type I and II pneumocytes intervenes. The entire surface of the alveolus is covered with surfactant, a phospholipid produced by the type II pneumocyte. Finally fibroblasts and mast cells occupy the interstitium and account for 36% of the cells. Two very important cells are the type I and type II pneumocytes. Type I pneumocyte is the air-exchange cell and type II is the cell that secretes surfactant that decreases surface tension so that alveoli do not collapse.

taste bud

Taste buds are embedded in the epithelium lining the moats of circumvallate papilla and in the surface epithelium of some fungiform papilla. Here is a specimen of a circumvallate papilla. When the moat is enlarged the light staining areas represent the location of taste buds. Further enlargement of a single taste bud shows its structure to have a pore facing and next to the lumen of the moat and different kinds of cells within the taste bud. This drawing shows two cell types. One is the sustentacular cell (colored blue) and the other cell that transduces the chemicals in solution into the different modalities of taste. The sustentacular cell plays the important role of supporting the delicate cells that pick up molecules and transduce them into nerve signals. The cells that do the transducing are modified epithelial cells called neuroepithelial cells (colored red). There is one more cell not illustrated here and that is the basal cell that is a stem cell. These cells provide replacement cells for the neuroepithelial cells. Taste bud cells are renewed about every 10 days.

saliva

The URL link at the top of this slide will take you to information about the buffering action of saliva provided by a Dental School at the University of Salivary Gland Immune Function Return to outline Salivary Glands contain antibodies Salivary glands participate in the humoral immune response Source of antibodies are Plasma Cells Located in the connective tissue Secrete secretory immunoglobulin A (IgA) Acinar cells have a secretory glycoprotein that binds with IgA from the plasma cell The secretory molecule aids in the passage of IgA from the plasma cell through the acinar cell to the lumen plasma cell S l Saliva Return to outline http://www.ncl.ac.uk/dental/oralbiol/oralenv/tutorials/bicarbonate.htm After modifications by the cells in the various ducts that saliva must pass through, the final product, saliva, has a pH of 6.3, nearly neutral, and is hypotonic. i Newcastle in the United Kingdom. If you are d including water, ions are either added or removed as 3 the forming saliva passes through the ducts. When relationship to the diagram of an acinus, intercalated e duct, striated duct and interlobular duct. After the initial secretion of either mucus or a serous substance 9 saliva enters the oral cavity it normally has a pH of 6.3 and is hypotonic. It contains immunoglobulin proteins, enzyme proteins such as amylase, lactoferrin and many other substances. Saliva initiates starch digestion by the action of amylase contributed by the serous cells in the parotid gland. Inorganic salts such as calcium phosphate and sodium chloride are components of saliva. Saliva functions to Lubricate and bind food --the mucus in saliva is extremely effective in binding masticated food into a slippery bolus that (usually) slides easily through the esophagus without inflicting damage to the mucosa. Saliva also coats the oral cavity and esophagus, and food basically never directly touches the epithelial cells of those tissues. Saliva Solubilizes dry food--in order to be tasted, the molecules in food must be solubilized. Saliva also contains lysozyme, an enzyme that lyses many bacteria and prevents overgrowth of oral microbial populations. Saliva functions as an Oral hygienic solution--the oral cavity is almost constantly flushed with saliva, which floats away food debris and keeps the mouth relatively clean. Flow of saliva diminishes considerably during sleep, allow populations of bacteria to build up in the mouth -- the result is dragon breath in the morning. curious, check it out. Observe the graph and its

clearing dust and bacteria from the nose and lung

The air we breathe is not clean. Depending on our environment at any time the air we breathe may contain a wide range of contaminants. There are two mechanisms resulting from structure design that are responsible for filtering and removing contaminants from the air we breathe. One involves a combination of cilia and mucus. The other involves the action of macrophages. From either deep in the lung or from the nasal cavity all of the pathways of clearance converge on the oral pharynx. This is accomplished by the respiratory epithelium which does two main things, 1) provides a coating of the airways with mucus having just the right viscosity and 2) through the work of the ciliated cells moves the mucus coat in the direction of the oral pharynx. The alveoli are cleared by the action of mobile macrophages which constantly police the alveolar walls looking for foreign substances such as dust, asbestos, other environmental contaminants and bacteria. Clearance of alveoli by these macrophages will be presented later in this lecture.

air blood diffusion barrier

The air-blood diffusion membrane (also called the air-blood barrier) consists of (from the air space in the alveolus to the lumen of the capillary) 1) a layer of surfactant, 2) a type I pneumocyte, 3) the fused basal laminae of the type I cell and the endothelial cell, and 4) the endothelial cell. Carbon dioxide diffuses from the blood to the alveolar space and oxygen diffuses from the alveolar space to the blood. Type I pneumocytes are covered by a layer of surfactant that is secreted by the type II pneumocytes.

alveolar septum and macrophages

The alveolar macrophage is in charge of keeping the alveolar spaces of all respiring airways (that includes the alveoli of respiratory bronchioles and alveolar sacs) cleared of particles, viruses, and bacteria. Particles 1 micron or smaller are suspended in the air longer and often will get as far as the alveoli so that these cells are very important in clearance at this level. They actually crawl along the surface of the alveolus engulfing anything that is not supposed to be there. They can crawl from one alveolus to another through small openings in the alveolar septae called inter- alveolar pores (pores of Kohn). After engulfing particles or erythrocytes in the case of congestive heart failure, these cells move into the interstitium of the alveolar septum, enter lymphatic capillaries and are carried to the hilum of the lung where they enter lymph nodes.

lips and oral cavity

The common name for the oral cavity is the mouth. Observe the location of the oral cavity - between the tongue, hard palate, teeth and oropharynx. This is the oral cavity proper. Entrance into mouth/oral cavity is via the lips. The first chamber encountered is the oral vestibule that is bounded by the inside of the lips and the teeth. Observe tongue that occupies much of the oral cavity. The tongue muscle is anchored into the hyoid and mandibular bones. Muscles extend from one mandible (jaw bone) to the other, attaching also to the hyoid bone. The floor of the oral cavity is formed by these muscles and they are covered with a mucosa that has stratified squamous non-keratinizing epithelium. Observe the location of the pharyngeal and lingual tonsils. In the next slide the gross boundaries of the lips will be illustrated.

bronchioles

The conducting airways continue from the trachea through several generations of bronchi into the smallest of the conducting airways, the bronchioles. As illustrated here, a bronchiole has no cartilage in it is wall, only smooth muscle and the lining is ciliated columnar epithelium with many Clara cells interposed in the epithelium. Clara cell structure and function will be explained on the next slide. Bronchioles are probably the most numerous of the conducting airways in the lung. They are very important in regulating the movement of air into the alveoli (moving air into the alveoli is called ventilation, a term commonly used in pulmonary physiology and function studies and analysis). Due to the large number, their small size and the smooth muscle in their walls, just a small reduction in their diameter causes a very significant increase in the resistance to airflow into the alveoli. Bronchioles are the structures most affected by asthma. Patients with asthma experience dramatic reduction in bronchiole diameter when they have an attack.

Hepatocyte & Liver Sinusoid

The details of the relationship between a hepatocyte and bile canaliculi and sinusoids is illustrated in this drawing. This view is as if a liver cord with its adjacent sinusoids, bile canaliculi and other hepatocytes in neighboring cords were cut in cross- section. Glycogen (stored in clumps), rough endoplasmic reticulum and smooth endoplasmic recticulum, aside from the nucleus, are three very important and essential organelles in the hepatocyte. Observe the three bile canaliculi that are always located between two adjacent hepatocytes. The canaliculi are formed by tight junctions between the hepatocytes at these locations. This makes a very tiny canal, 1 - 1.5 microns in diameter, that carries bile away from the hepatocyte. Bile is secreted into these canaliculi from the hepatocyte by exocytosis. The other surfaces are bordered by sinusoids that are lined with an endothelium. Within the sinusoid are special phagocytic cells call Kupffer cells. These cells attach themselves to the endothelial cells often with their processes spanning the sinusoid to catch and take in foriegn substances like bacteria. Observe the gaps in the endothelial lining. The gaps are large enough so that plasma bathes the surface of the hepatocyte in a space called the space of Disse, but small enough that formed elements of the blood cannot pass into this space. Microvilli project into the space of Disse. The microvilli provide an increase in surface area for interchange between the plasma and the hepatocyte. Thus, formed elements of the blood can be whizzing by at a pretty good clip while the hepatocyte is constantly exposed to plasma. In the space of Disse there is a special cell called the Ito cell (alias 'fat storing cell' or 'stellate cell'). These cells store vitamin A. Vitamin A is released from these cells, transported to the retina where it contributes to the formation of rhodopsin, the visual pigment of the rods and cones. In certain pathological conditions these cells lose their pigment and, in the case of inflammation or cirrhosis, secrete collagen that forms scar tissue in the place of hepatocytes that were damaged by alcohol or infection.

upper and lower respiratory tracts

The division of the respiratory tract into upper and lower divisions is useful in the diagnosis and treatment of infections and diseases unique to either. The upper tract consists of the nasal vestibule, the nasal pharynx and the larynx. The lower tract consists of the trachea, bronchi, bronchioles, respiratory bronchioles, alveolar ducts and sacs.

The enterocyte, also referred to as the surface or intestinal absorptive cell

The enterocyte, also referred to as the surface or intestinal absorptive cell, has multiple functions. Amino acids, glucose, fatty acids and glycerol are absorbed through the apical cell membrane. The apical cell membrane has very tiny projections called microvilli. When viewed in the light microscope as the image below and left, the microvilli density is so great that the apical end of the cell has a border that has been referred to as a striated border (because at a 100x magnification you can just make out lines between the microvilli so it appears striated). (some texts call this a brush border, more commonly brush border refers to the border of the proximal tubule cells of the kidney) If the border is magnified and examined with an electron microscope you can easily see the individual microvilli that are 1 - 2 microns long. These microvilli increase the surface area of the tip of each absorptive cell 200 times over a cell with no microvilli of the same dimensions. Observe that each absorptive cell is attached to others around it by a junctional complex that includes very tight junctions so that molecules cannot pass between the cells; they must pass through the absorptive cell. If the microvilli are enlarged further it is seen that there is a very complex glycocalyx (a complex of molecules anchored in the cell membrane and projecting into the lumen). This helps to trap enteropeptidases that work to carry out the final breakdown of peptides into amino acids.

renal corpuscle

The epithelial cells of Bowman's capsule, the endothelial cells of the capillaries of the glomerulus and the special connective tissue cells, mesangial cells, which fill in between the capillaries, all make up what is known as the renal corpuscle. (Recall that the lymphatic nodules in the spleen are called 'splenic corpuscles'). The renal corpuscle has a vascular pole where the afferent and efferent arterioles carry blood into and collect blood from the glomerular capillaries. At the opposite end is the urinary pole at which site the proximal convoluted begins. The lumen of the proximal tubule is continuous with the urinary space at the urinary pole. The glomerulus consists of several loops of capillaries the lumens of which are continuous with those of the afferent and efferent arterioles. The endothelium of the glomerular capillaries is enclosed with the visceral layer of Bowman's capsule. The parietal layer of Bowman's capsule lines the wall of Bowman's capsule. At the vascular pole the end of the distal convoluted tubule touches the afferent arteriole. At this point the cells of the distal tubule change orientation so that the apical ends are facing the afferent arteriole. This collection of cells is known as the macula densa (literally means a dense spot because the cells are so close together). Finally,there are the mesangial cells of the glomerulus. Mesangial cells are specialized pericytes located among the glomerular capillaries. They function to provide structural support for and regulate blood flow of the glomerular capillaries by their contractile activity. Some of them secrete collagen and laminin that keeps those components of the basement membrane renewed. Mesangial cells are also phagocytic. They help keep the basement membrane cleared of complex immunoglobulins that can clog the filtration membrane. Now we shall examine the structure that forms the filtration membrane in the glomerulus.

GI Tract, Oral Cavity - Anus General Plan

The gastrointestinal tract begins with the oral cavity and concludes at the anus. Before we begin with the detailed histology of each segment of the GI tract it is helpful to the basic organization of the GI tract. The GI tract can be thought of as a hollow organ as compared to the various glands that empty into it, as for example, the parotid gland that is a solid organ. Hollow organs, unlike solid organs, contain a large lumen around which there are layers that perform specific functions because of how they are organized and the tissues they contain. Here we see the general plan of the GI tract that consists of 4 layers. The 4 layers are, 1) Mucosa- consisting of an epithelium that may be formed into glands with an underlying bed of loose connective tissue and a muscularis mucosa (except not in the oral cavity as was the case in the respiratory and urinary tracts including the urinary bladder), 2) the Submucosa- consisting of loose connective tissue, nerve plexi, and glands, 3) the Muscularis externa- consisting of layers of smooth muscle, nerve plexi and 4) the Adventitia or Serosa. The adventitia consists of loose connective tissue that blends with the connective tissue of an adjacent region. If a segment of the GI Tract is exposed to a body cavity, then the loose connective tissue is lined with a mesothelium forming a serosa. As the different segments of the GI tract are presented we will see how the tissue and their organization within the 4 layers changes in each segment to allow for the function that segment performs.

kidney appearance

The image is a photograph of a normal kidney taken at autopsy showing how it appears. Observe that it is shaped like a bean. It is deep red colored due to the enormous amount of blood flowing through and contained within the kidney. Its surface is smooth because, except for its posterior aspect, it is covered with a serosa composed of mesothelium and loose connective tissue. As you can observe in this photograph of an unfixed, fresh kidney, the surface is also shiny or glistening. This is due to the mesothelial covering. It reminds one of 'saran wrap'. The loose connective tissue of the serosa blends the underlying capsule of the kidney that is composed of dense connective tissue. This inset is a microscopic view of the serosa and the capsule. The dense connective tissue of the capsule on the posterior aspect of the kidney is not covered with a serosa. The capsule there blends in with the connective tissue of the fascia of the deep muscles of the back. The capsule of the kidney supports and contains the delicate tubules that make up the bulk of the kidney. The hilum of the kidney is where the renal artery and vein carry blood into and out of the kidney....and where the ureter is attached.

pancreas endocrine and exocrine

The islet of Langerhans is easily identified in this slide. The surrounding tissue is arranged into acini & comprises the exocrine portion. Islets are usually lighter staining in histological sections and they are often oval-shaped.

The Juxtaglomerular Apparatus

The juxtaglomerular apparatus literally means an apparatus next to or very intimately associated with the glomerulus. It is located at the vascular pole and consists of special smooth muscle cells of the afferent arteriole that synthesize and secrete upon proper stimulus, renin, and the macula densa which is the collection of cells of the distal tubule in direct relationship to the afferent arteriole smooth muscle cells that contain the renin. Observe the cartoon that illustrates these relationships. The juxtaglomerular apparatus regulates blood pressure. Renin is the active substance that is released and then converted to angiotensin I and eventually to angiotensin II in the lung. Angiotensin II is a powerful vasoconstrictor that targets the smooth muscle cells of arterioles. Renin is released from the cells of the afferent arteriole by either mechanoreceptors that sense a change in length of the smooth muscle cells due to a fall in blood pressure, or, by a decrease in sodium in the distal convoluted tubule. The cells of the macula densa sense this change in sodium concentration and convey that to the cells in the smooth muscle of the afferent arteriole that contains renin.

kidney location

The kidneys are located in the abdominal region at a level between Thoracic Vertebra 12 (T12) and Lumbar Vertebra 3 (L3). The left kidney is located slightly superior to the right kidney. If a cross- section were made at the level of the dotted line the image on the right displays what would be seen. The right and left kidneys can be seen to be located in the posterior part of the abdomen surrounded by fat. Even in the thinnest persons, there is always some fat surrounding the kidneys. The fat serves to protect and cushion the kidneys from injury. They are located posterior or behind the peritoneum - retroperitoneal location. Underneath the peritoneum (serosa) is a capsule composed of dense connective tissue. A normal life can be lived with only one kidney so there is 100% backup in kidney function.

fundic gland cell types

The largest distribution in the stomach of the three types of glands - cardiac, fundic and pyloric - is of the fundic type of gland containing cells that secrete hydrochloric acid and pepsin, the main components of gastric juice. Although the glands are traditionally named Fundic Glands, they are just in the Fundic region. They are present throughout the body as well as the fundic regions of the stomach. Starting at the bottom of the fundic gland, the enteroendocrine cells produce specific stimulatory/inhibitory substances such as gastrin and somatostatin. Chief cells (also called zymogenic cells) are primarily responsible for producing pepsinogen which will be converted into the highly active proteolytic enzyme pepsin. These cells also produce lipase. Parietal (also called Oxyntic from a greek word meaning to make acid) are involved primarily in producing the components of hydrochloric acid through the intermediary enzyme carbonic anhydrase (details of this process in a subsequent slide). These cells also produce gastric intrinsic factor, a glycoprotein that binds to vitamin B12 so that it can be absorbed in the small intestine. A deficiency of vitamin B12 results in the development of abnormal erythrocytes that are too large but do not have an increased amount of hemoglobin. The result is that the average erythrocyte has a lower than normal concentration of hemoglobin, the oxygen carrying molecule. The name for the disease was first termed pernicious anemia because, before the cause was discovered, the disease was often fatal. Now it is treatable with the oral administration of vitamin B12 (it is absorbed by the oral mucosa) or, in difficult cases, intravenous administration of vitamin B12. Now the common name for the condition is megaloblastic anemia (large red blood cells with an inadequate amount of hemoglobin). Mucous neck cells have a different type of mucus from the surface cells. The vesicles are at the apical end of the cell & they stain intensely with PAS. The surface lining cells produce mucus continuously. Regenerative cells provide renewal cells both up & down the gastric gland. Unlike stem cells of the small intestine which are located in the base of the gland, these reside in the neck region. Surface lining cells produce a thick mucus covering which becomes infiltrated with carbonate, the other dissociative product of carbonic acid, to aid in the prevention of self digestion.

parenchyma cells of salivary gland

The parenchymal cells that form the parenchyma of salivary glands are displayed in this slide. Observe the difference between mucous cells, serous cells and the unique combination of mucous and serous cells that forms a serous demilune. Observe the difference in the three types of ducts. Intercalated duct consisting of a wall composed of simple cuboidal epithelium. The striated duct consisting of a wall composed of simple columnar epithelium that is specialized to absorb from and secrete into the lumen with its basal cell membrane infoldings and mitochondria. Thentheexcretoryduct,thewall of which is composed of stratified cuboidal or stratified columnar epithelium.

esophagus epithelium

The lumen of the normal esophagus is lined by a tough, nonkeratinizing, stratified, squamous epithelium. The lower border of the squamous epithelium is irregular due to the presence of transitory folds of the lamina propria and more particularly, due to the presence of high conical papillae of connective tissue. These papillae are highly vascularized. On routine microscopy the squamous epithelium can be divided into the stratum basale (SB) where stem cells are located next to the basal lamina, the stratum spinosum and the stratum superficial (superificiale). The stratum spinosum can be divided into an intermediate or suprabasal layer (SL) and a differentiated layer (DL) that is more superficial. Most of the proliferating cells in this epithelium are in the supra basal layer. In the differentiated layer (DL) layer the cells contain glycogen, a mark of maturity. The most superficial layer is composed of several layers of cells that are flattened and show signs of dying. These cells are soon to be lost into the lumen (a process known as desquamation). These cells with their glycogen content will add to the mucus in the lumen. Langerhans cells (recall these from the epidermis as antigen presenting cells) and cytotoxic T-cells are commonly seen in the epithelium of the esophagus. Several are encircled in the inset from the boxed in region. Throughout the GI tract cells of the immune system are constantly monitoring for antigen and respond with either a humoral or cellular response.

respiratory bronchioles

The lung air passageway continues from the terminal bronchiole into the respiratory bronchiole. Respiratory bronchioles are the first segment of the respiring lung air passageways. The term respiring refers to the fact that these airways contain alveoli so that gas exchange takes place in their walls. A cross-section of a respiratory bronchiole reveals the wall structure, in this illustration, to be made up of three alveoli with simple cuboidal ciliated epithelium intervening between the alveoli. Patches of smooth muscle are present as part of the wall structure. The smooth muscle provides the means for small changes in the diameter of these airways.

lung specimen at low mag

The lung is a solid organ with no cortex or medulla. The histology of the lung is arranged around its airways. The larger airways like the bronchi and bronchioles, exclusive of the alveoli (smallest airways seen here as very tiny spaces) are small hollow organs having layers of tissue around a lumen. They are actually small hollow organs within the lung, a solid organ. This is how a fixed while inflated lung specimen stained with H & E looks in the microscope at low magnification. Over all there are many air spaces. You can see large blood vessels and airways readily in this specimen. The smallest airspaces are alveolar spaces. The larger spaces are airways and the red stained areas next to them are blood vessels. The pulmonary arteries coarse very close to the airways even down to the respiratorybronchioles. Thepulmonaryveins other than those next to the bronchi separate from the airways running independently of them.

gall bladder mucosa

The mucosa of the gallbladder includes the epithelium consisting of tall simple columnar cells & lamina propria which is directly associated with the muscular externa layer. There is no muscularis mucosa included in the mucosa of the gallbladder. An enlargement of part of one of the folds shows the mucosa in greater detail. Observe that the columnar cells are tall and that there are no goblet cells. Sodium and chloride (and bicarbonate) are actively transported from the lumen across the epithelium into the lamina propria. The protein pumps that move these molecules are located in the baso-lateral cell membranes.

nasal cavity olfactory region

The mucosa of the nasal cavity covering the superior concha is specialized containing bipolar neurons that have receptors for dissolved substances. These substances are molecules from a myriad of odiferous chemicals.

olfactory epithelium

The olfactory epithelium consists of the olfactory cell that is a bipolar neuron, supporting cells that provide stable support for the neurons and basal cells that serve as stem cells for renewal of the olfactory cells. The surface area of contact between odiferous molecules and the olfactory cell is formed by modified cilia extending from the olfactory cell and lying in a dense matt on the surfaceoftheolfactoryepithelium. These modified cilia are non-motile, i.e. they do not move. The olfactory glands of Bowman, which are serous protein secreting cells, make and secrete an odorant binding protein, ODP, which binds to odorant molecules and then the complex binds to the plasma membrane of the modified cilia. The olfactory cell axon synapses with neurons in the olfactory bulb located in the brain. The olfactory cell - the bipolar neuron - is the cell that is responsible for transforming the presence of a molecule in the nasal cavity to a sense of smell that is registered to our consciousness in the brain. Observe also the plasma cell. Beginning with the nasal cavity mucosa and continuing throughout the conducting airways, the connective tissue of the mucosa includes a population of plasma cells that serve to provide specific antibodies as the final response of the humoral immune response.

pancreas

The pancreas closely resembles the parotid gland with which it can be confused because all of its secretory units have serous cells making up the acini. The pancreas differs from the parotid gland in that it has no striated ducts and it contains an endocrine gland within itself, the islets of Langerhans.

Liver Parenchyma & Stroma

The parenchymal cells of the liver are the hepatocyte, the von Kupffer cell and the fat storing cell of Ito. Hepatocyte cytoplasm includes patches of rough ER to synthesize a variety of proteins the include albumin and fibrinogen among many others. Hepatocyte nuclei vary in size from small to large and some cells may be have two nuclei (binucleated). One binculeated hepatocyte is encircled in the left upper iimage. Hepatocyte nuclei are euchromatic that correlates with the function of protein synthesis. The enlargement in the lower left small image shows the detail of several euchromatic nuclei. Von Kupffer cells can be identified by their stellate shape and having more cytoplasm visible than the endothelial lining cells as indicated in the middle large image. Von Kupffer cells function to phagocytize bacteria and other foreign substances that may inadvertantly enter the liver sinusoids from the intestines. The middle lower image shows a von Kupffer cell clearly located within a sinusoid. The stroma is composed of reticular fibers that surround the blood vessels, nerves and bile ducts in the portal areas and also in the space of Disse as illustrated in the silver stained specimen on the right.

roof of oral cavity

The roof of the oral cavity consists of the hard and soft palates. The hard palate consists of bone covered with a submucosa and mucosa.

parietal cells

The parietal cell gives the appearance of "sunny side up" eggs with its prominent acidophilic cytoplasm & centrally located nucleus. This is due to the large amount of membranous material in the cell referred to as an intracellular canaliculus when at rest. The membranous system consists of an intracelluar canalicular and tubulovesicular system that increases the membrane surface area for the molecules that participate in the formation of hydrochloric acid. The cells also have a very high density of mitochondria that provide the energy required to actively transport hydrogen ions across the plasma membrane into the lumen of the stomach. Recall that cell membranes, cytoplasmic membranes and mitochondria have a dominant population of basic proteins that react with the acid dye eosin. That is the reason why these cells are acidophilic staining intensely pink with eosin.

Extra-Pulmonary Primary Bronchus hilus of the lung where vessels/airways enter and leave

The primary bronchi have a short segment that is outside of the lung and these segments are called extra-pulmonary bronchi. This is a cross-section of a bronchus just outside of the lung in the hilus of the lung, the region where bronchi enter and blood vessels enter and leave the lung. Observe that the cartilage is no longer a complete C shape, but now is present as plates. Lymph nodes are abundant at the hilus of the lung. All of the lymphatic drainage coming from the lung passes into and through these lymph nodes.

salivary gland parenchyma and stroma

The prominent white lines seen in this very low magnification of a histological section through a salivary gland are the connective tissue septa that divide the parenchyma into lobules. This is the stroma of the gland. The gland is enclosed by a connective tissue capsule from which the septa project into the gland. The parenchyma is the specific cell type of that organ that actually performs the organs function, such as secretion. In this histological section the secretory cells in the acini are reflected in the blue staining. The ducts can be seen as small pink areas. Duct cells are considered to be a component of the parenchyma of the gland. The terms stroma & parenchyma apply to all organs.

respiratory system overview

The respiratory system consists of the respiratory tract and the lungs. The respiratory tract begins with the nasal cavity where special cells are located that provide the sense of smell. The entrance to the nasal cavity is a short region known as the nasal vestibule where the lining is skin with hair. The hair helps filter the air as it enters the nasal cavity. The respiratory mucosa lining the nasal cavity and the blood vessels underlying moisten and warm the air before it goes into the next part of the respiratory tract. Next is the larynx (the voice box) where a special ligament (true vocal cord) vibrates by the force of air passing producing sound, the pitch of which is altered by the tension put on the vocal cord by the vocalis muscle (striated muscle). The air then flows into the trachea that conducts air from the larynx to two airways arising from branching of the trachea, the primary bronchi that continue into the lung. The wall structure of the trachea includes c shaped cartilage rings that keep the trachea from collapsing when air is breathed in and out. The first respiratory tract structures in the lung are bronchi that are airways containing plates of cartilage to maintain open air passage ways -several generations, secondary, tertiary etc. bronchi that distributed the air throughout all regions of the lung. The tract then continues into the bronchioles that are small airways with several layers of smooth muscle in lieu of cartilage. These airways can increase or decrease the resistance of airflow by smooth muscle contracting to change the lumen diameter. Finally, several segments of a hybrid structure - respiratory bronchioles that both conduct air and provide for gas exchange that lead into the 300 million small air sacs called alveoli where the definitive action of gas exchange takes place. Learning the histology of the respiratory system is learning the wall structure and lining of the airways and the detailed structure of the site where gas exchange takes place.

conducting and respiring airways

The respiratory tract is composed of segments that conduct air and segments that exchange gases (oxygen and carbon dioxide). Conducting means the transportation of something. Respiring means the exchange of gases between the air space in the lung and the blood. The respiring airway epithelial lining, which, said another way is the lining of all of the lung alveoli, constitutes a surface area in the average adult equal to the surface area of a tennis court. The histological organization of the lung is designed to enclose this much surface area in the thorax; an amazing accomplishment if you stop to think about it!

alveolar duct, sac, and alveioli

The respiring airways continue as alveolar ducts, then alveolar sacs, then, finally, alveoli. From this point on the epithelial lining is simple squamous epithelium with an occasionally cuboidal epithelial cell. This drawing illustrates the difference between an alveolar duct, an alveolar sac and an alveolus. Note the resemblance of an alveolar duct to a hallway with many doors opening into rooms. Observe the red knops in the alveolar duct that are between each of the alveoli making up the bulk of the alveolar duct wall. These red knobs are meant to illustrate sections through the spiraling smooth muscle bundles in the duct wall. Note in the lower left the cross-section through two winds of the rubber band like strands of smooth muscle in the wall of an alveolar duct. The atrium is simply like a large foyer of a house which opens into several rooms (alveolar sacs). Alveolar sacs are nothing more than sacs of alveoli.

gastric glands

The three types of gastric mucosal glands- cardiac, fundic & pyloric- are illustrated here. They are classified as simple tubular glands. Short epithelial lined pits project inward and to each of these pits one, two or three tubular glands may be attached and empty their products into the pit and from there into the lumen of the stomach. The cardiac glands have short pits with coiled tubes that have a wide lumen. They produce mucus and lysozyme. Fundic glands have relatively short pits with very long tubes which are usually branched, up to 3-7 per pit. They produce the gastric juice of the stomach that includes HCl, pepsinogen (converted to pepsin by HCL), intrinsic factor, mucus. The secretions are produced by specific cell types. Hydrochloric acid secreted by parietal cells begins the digestion of dietary protein by hydrolyzing the peptide bonds breaking the protein down into various sized polypeptides. Parietal cells also secrete intrinsic factor, a glycoprotein that binds to vitamin B12 that is essential for B12 to be absorbed later in the ileum of the small intestine. Pepsin secreted by chief cells (converted from a precursor, pepsinogen by HCL) is a potent proteolytic enzyme that breaks polypeptides into smaller units, peptides. In the small intestine other enzymes break the peptides down into amino acids. Pyloric glands have long, deep pits that connect to coiled tubes. Pyloric glands produce mucus, lysozyme, and gastrin by G cells and somatostatin by D cells. All three glands have mucous cells that produce mucus. Mucus provides an acid protecting coating of the cells lining the stomach. Both G and D cells are neuroendocrine cells and their secretions are classified as hormones. Gastrin stimulates parietal cells located in the fundic glands that secrete HCL and intrinsic factor. Although gastrin and somatostatin hormones are secreted by neuroendocrine cells in all three gastric glands, most of the cells secreting these are located in the pyloric glands.

the ureter

The ureter has a mucosa consisting of transitional epithelium, a basal lamina and loose connective tissue. The lumen is often stellate or star shaped in histological sections due to the contraction of the smooth muscle between harvesting the tissue and fixation. Contraction of the smooth muscle in the wall causes folding of the mucosa. The muscle arrangement of smooth muscles in the ureter is inner longitudinal and outer circular. This arrangement makes it possible for the ureter lumen to become larger or smaller in diameter, and the longitudinal muscle makes it possible for the ureter to literally move urine toward the urinary bladder by a 'milking' process. The ureter is wrapped with loose connective tissue, the adventitia.

urinary bladder

The urinary bladder is shaped like a ball and it has also three layers, a mucosa, a muscle layer and an adventitia. The epithelium of the mucosa is also transitional epithelium. The smooth muscle fascicles envelope the bladder in bands that course in multiple directions. Think of the urinary bladder as a ball around which you wrap rubber bands (smooth muscle fascicles) until you have multiple layers running in all directions so that when the bands of smooth muscle contract in a coordinated manner, the ball becomes smaller and smaller to squeeze urine from the bladder into the urethra. If you have ever taken the cover off of a golf ball, particularly the older ones, then you can picture this. At least the older golf balls are wrapped with many, many rubber bands oriented in every way imaginable. The superior and lateral aspects of the bladder are wrapped with a tunic called the serosa that is the same as the peritoneum, a loose connective tissue covered with a simple squamous epithelium (a mesothelium). The anterior and posterior surfaces of the bladder are covered with an adventitia, a loose connective tissue similar to the outer covering of the esophagus.

centroacinar cell

The very beginning of the duct system in the pancreas is defined by the centroacinar cell at the mouth of the acinus. They are the intra-acinar portion of the intercalated duct. Circled structures are centroacinar cells.

permanent teeth

There are 32 permanent teeth. All have the same histological structure. This is the natural color of teeth- whitish enamel, ivory dentin. The enamel here covers the anatomical crown of each tooth. The crowns have different shapes and indentations dependent on what tooth is encountered among the incisors, cuspids, premolars and molars. Some teeth have a single root, others two roots and others have multiple roots.

colon histology

There are no villi in the colon but it is rich in goblet cells & GALT. The mucosa has absorptive cells bordering the lumen, but the intestinal glands are lined with nearly 100% goblet cells. There are no glands in the submucosa that consists of loose connective tissue that may contain a variable amount of adipose tissue with blood vessels nerves and lymphatics. In the mucosa and often projecting into the submucosa there is often lymphoid tissue that is diffuse or in aggregates that may contain lymphatic nodules (GALT). The muscularis externa consists of an inner layer of smooth muscle that is oriented circularly and an outer layer of longitudinallyorientedsmoothmuscle. Inthe colon, this outer longitudinal layer of the muscularis externa is organized into three thickened bands with the region between the bands being very thin. The three thickened bands are called the Taenia Coli. Taenia is from a Greek word meaning band or ribbon. Coli means colon. When these bands contract they create a series of puckers in the intestinal wall call haustra. These are little sacculations. The action of the inner and outer longitudinal muscle of the muscularis externa helps to compact the feces. Finally the outer wrapping of the colon is a serosa.

facet cells in a relaxed or contracted bladder

This additional illustration is included for clarity in the explanation of how the facet cells of the urinary bladder epithelium function to allow stretch of the epithelium without tearing. In a distended bladder the vesicles fuse with the surface membrane to expand its area and in a collapsed or empty bladder parts of the surface cell membrane are incorporated back into the cytoplasm as vesicles.

Bile Formation and Secretion

This diagram shows the basic metabolic pathway for the formation of bile. Bilirubin, a breakdown product of hemoglobin, is brought into the cell & complexed with glucuronate via glucuronyltransferase to form the water soluble bilirubin glucuronide. This, along with bile salts such as cholic acid makes up bile. Bile is transported through the canaliculi, then by bile ducts in the triads, then large ducts and finally into the gallbladder for storage. Water makes up a good portion of bile. In the gall bladder a significant portion of the water is reabsorbed by the gall bladder epithelium so that the stored bile is a concentration of bile salts and bile pigment.

plicae circulares

This drawing illustrates the fact that the plicae circulares are folds of the intestinal mucosa with the submucosa occupying the core of the folded mucosa. Another term for a plica circularis is valve of Kerckring

the rectum and anal canal

This slide illustrates the epithelial histology at the pectinate line where the epithelium transitions from simple columnar epithelium to stratified squamous non-keratinized epithelium.

renewal of intestine cells

This slide illustrates the location of regenerating cells in the wall of the intestine gland. These cells provide replacement cells for all of the cell types in the intestinal gland and the epithelial covering of the villi. The next slide will show this cycle of stem cell - specific cell types - loss of cells at the tip of the villi.

classic liver lobule

This drawing of a wedge of a lobule illustrates the relationship between the hepatocytes, the sinusoids (that receive blood from the hepatic artery and portal vein) and the bile duct that drains bile from the lobule. A liver lobule consists of stacks of anastomosing plates of hepatocyte one cell thick separated by anastomosing sinusoids. Blood flows from the hepatic artery into the sinusoids and in collected by the central vein. Bile, secreted into small channels called bile canaliculi by liver cells (hepatocytes) flows in the opposite direction into slightly larger channels first, bile ductules and finally into bile ducts located in the portal areas. A liver lobule is on the order of 2mm high and 0.7 mm in diameter. It is actually a 3 dimensional hexagon. In this drawing of an ideal liver lobule sectioned across its long axis, we see that it is shaped like a hexagon. The central vein is at the center and the six portal areas form the six points of a hexagon. Connective tissue encloses the structures in the portal areas and extends also to wrap the liver lobule at its perimeter. In humans there is only a small amount of connective tissue at the perimeter so that it cannot be observed readily in an H & E section. A pig's liver has much more connective tissue that is easily observed. A cow's liver has an amount between the human and pig. Pig liver is tough when cooked for eating but a cow's liver is tender.

salivary gland

This drawing shows the overall structure of a salivary gland. Salivary glands are multicellular glands that are organized into secretory units composed of mucous and/or serous acini that empty their contents into a series of ducts. They are classified as compound because they have ducts that branch. They are classified as either acinar or tubuloacinar depending on whether they have only acinar secretory units or have a combination of tubules with acini. Observe that the gland has divisions called lobules. Within each lobule are multiple secretory units composed of either serous or mucous cells, or sometimes a mixture of these cell types. The secretory units in a lobule each empty into a single intercalated duct. Intercalated ducts empty into larger ducts, the intralobular or striated duct. These are lined with simple columnar epithelium. The secretions from each lobule are then collected by lobar ducts and, finally, all of the lobar ducts empty their contents into the main duct leading from the gland. Lobar ducts and the main ducts have stratified columnar epithelium. Each of the major salivary glands has a capsule composed of connective tissue and from the capsule connective tissue divisions (septa) project inward dividing the gland into the lobules. This connective tissue framework is the stroma of the gland (the solid organ). The secretory cells constitute the parenchyma of salivary glands. Salivary glands do not have a cortex or medulla.

the triad

This drawing shows the relationship of the bile duct, portal vein and hepatic artery as they course through the liver. Liver parenchyma is organized into lobules, two of which are indicated in this drawing. The 'triad' is intimately related to the liver lobule. They are distributed around the peripheral aspect of each lobule providing blood from the hepatic artery and portal vein into the lobule and draining blood from it by a tributary of the hepatic vein - the central vein. Bile secreted by the liver cells is drained from the lobule by the bile ducts.

intestines histological organization

This drawing will serve to present an overview of the gastrointestinal tract from stomach to large intestine. The surface epithelial lining from the stomach to the anal canal is simple columnar. The stomach and intestines are bound to the posterior abdominal wall by a mesentery. The two layers of mesothelium split when the mesentery reaches the intestines and surrounds them. This mesothelial layer and a small amount of connective tissue beneath constitute a serosa, which in the case of the stomach and intestines is the visceral peritoneum. The liver and pancreas are accessory glands to the intestinal tract and their secretions enter the intestinal lumen via a major duct that passes throughthewalloftheduodenum. Throughoutthe stomach and intestines Auerbach's and Meissner's plexus are present. The duodenum is characterized by having villi and submucosal glands (this and the esophagus are the only two locations from esophagus to the anus where submucosal glands are present). The remainder of the small intestine, the jejunum & ileum, have villi. Special folds of the mucosa called plica circularis are located mostly in the small intestine with a few folds in the colon. These folds add to the surface area of the lumen of the intestine. The ileum is characterized by having villi in the mucosa and large masses of lymphatic nodules in the mucosa and submucosa (Peyer's Patches). Finally the colon is characterized by having no villi - only mucosal simple tubular glands with a dominate presence of goblet cells.

filtration membrane

This figure from Kierszenbaum's Histology & Cell Biology text nicely demonstrates and illustrates the relationship between the structures of the filtration membrane and how they perform the function of filtration. First to note is that the fenestrations in the endothelial cells have no diaphragms so that proteins, electrolytes, water etc can flow easily out of the plasma into the basement membrane. However, the fenestrations are no more than 90 nanometers in diameter.....much too small for any of the formed elements of the blood to pass. So that is a first order of filtration to keep the formed elements within the lumen of the capillary. The next important aspect to know is that the glycoproteins extending from the cell membrane of the endothelial cells are negatively charged. This slows down the passing of large anionic proteins in the plasma of the blood. The basement membrane and the cell membrane of the foot processes also are heavy in negatively charged glycoproteins that add to the slowing of passing of large anionic protein molecules. Finally, the filtration slit diaphragm is like a sieve that further filters proteins. The final result is that some albumin makes its way into the urinary space, but larger proteins of the blood plasma like gamma globulins are unable to pass through.

Cilium: Cross-section TEM view

This is a cross-section of a cilium as viewed in a transmission electron microscope at 400,000 X magnification. Observe that each microtubule (25 nanometers in diameter) is made up of monomers of the protein tubulin assembled together. The protein nexin serves as a tether to limit the sliding action of the microtubules, and the ATP dependent function of the protein dynein that induces the adjacent microtubules to slide against each other that results in the bending of the cilium. Let's look at this action in the next slide.

Tongue Muscle: striated skeletal

This is a cross-section of a portion of the oral cavity and surrounding structures (lower jaw and floor or oral cavity) of a mouse. It is used to show the tongue and its relationship to the teeth on either side and how the tongue is really a bag made up of mucosa with striated skeletal muscle as it contents. Observe the mylohyoid muscle that contributes to the floor of the oral cavity. The boxed in area when viewed at higher magnification shows that the muscle bundles run in several different directions. The muscle within the tongue has bundles running longitudinally, horizontally and vertically. This enables one to move the tongue in almost any direction. These are the muscles within the tongue and as a group they are called the intrinsic muscles. In addition there are extrinsic muscles of the tongue that enable the tongue to be retracted in the mouth or stuck / protruded out of the mouth. The extrinsic muscles reposition the tongue, while the intrinsic muscles alter the shape of the tongue for talking and swallowing. This further enlargement of tongue muscle demonstrates that it is striated skeletal muscle.

alveolar septum capillaries

This is a cross-section through a capillary within an alveolar septum. Observe the capillary formed by an endothelial cell and note the endothelial cell nucleus. Observe the erythrocytes within the capillary. Observe that the endothelial cells are fastened together with tight junctions. The air-blood barrier is very thin, on the order of 0.1 - 1.5 microns thick.

Respiratory Epithelium: Pseudostratified Ciliated Columnar Epithelium

This is a drawing of the so-called respiratory epithelium. The name is meant to denote that it is the epithelium that lines the respiratory tract - specifically most of the conducting airways. Five types of cells make up PSCC epithelium - ciliated cells, goblet cells, brush cells, neuroendocrine cells and basal cells. The function of ciliated cells is to provide cilia for the motor of the mucociliary escalator that you soon learn bout, and the exact amount of chloride ions in the lumen to have the right viscosity of mucus which is secreted by the goblet cells. Basal cells are stem cells which provide multipotent cells for renewal of the others. Neuroendocrine cells have small electron dense granules which secrete a varietyofpeptides. Theyarealsoknownas 'small granule cells' or DNES (Diffuse Neuroendocrine System) cells. Brush cells are absorptive cells.

tooth root

This is a histological cross-section through the root of a tooth showing the relationship between the tooth and the surrounding bone. In the center is the pulp, a loose primitive connective tissue containing blood vessels, nerves and odontoblasts (you can just barely make out the layer of odontoblast cells at the border between the pulp and the dentin). Observe the thin coat of cementum covering the dentin (slightly more basophilic than the dentin) and the periodontal ligament between the dentin and the bone.

interalveolar septum type 1 and 2 cells

This is a histological section showing a view at high magnification of several alveolar septae and alveolar spaces. Observe that the air-blood barrier is very thin. You can get an idea of just how thin this membrane is by comparing the size of the RBCs in this field. Especially note the RBC indicated by the red dotted line arrow that shows a side profile. The middle light staining region of an erythrocyte is about 0.8 microns thick. The air-blood barrier ranges from 0.1 - 1.5 microns in thickness. Note the round nucleus and rounded shape of the type II pneumocyte contrasted with the flattened nucleus and flattened cell shape of the type I pneumocyte.

renal lobe low mag

This is a histological section through the cortex and medulla of a single renal lobe stained with hematoxylin and eosin. The dotted line is the boundary between the cortex and medulla. A renal lobe is a pyramidal shaped portion of the medulla with its associated cortex. There are 7 kidney lobes in the average human. Observe that glomeruli are only present in the cortex. Observe the triangular shape of the medulla in this lobe (it is pyramid shaped in the 3rd dimension). Observe the apex of the renal pyramid at the renal papilla where urine is emptied into a minor calyx. The image on the right is this same specimen only with two nephrons and collecting ducts overlying the histological specimen. The nephron begin with a Bowman's capsule that contains a tuft of capillaries, the glomerulus (red), Continuing from Bowman's capsule and sharing a continuity with its lumen are proximal and distal convoluted tubules with loops of Henle intervening between the two convoluted tubules. Observe that each of the two nephrons is connected and empties their contents into a collecting duct. The combination of a nephron and it collecting duct is called a uriniferous tubule. Each kidney has on the order of one million nephrons. With each kidney lobe the nephrons are organized into collections residing in several lobules. The nephrons that drain into a single collecting duct make up the tissue that forms a lobule. Blood is delivered to two adjacent lobules via an interlobular artery. Next the blood vessels of the kidney will be presented, followed by the structure of the lobules and then the detailed structure and function of a nephron, the functional unit of the kidney.

intrapulmonary bronchus

This is a longitudinal section of a bronchus within the lung. Observe the alveoli surrounding the bronchus, confirming that its location is within the lung. Bronchi have plates of cartilage not rings which are exclusively present in the trachea.

esophagus histology

This is a low magnification view of the entire thickness of a histological cross-section of the esophagus stained with hematoxylin & eosin. Observe the layers: mucosa, the submucosa with mucous glands, the muscularis externa composed of an inner layer of circularly arranged muscle and an outer layer of longitudinally oriented muscle. Wrapping the outside of the esophagus is the adventitia. The upper one third of the esophagus has a large amount of striated skeletal muscle that functions to aid in voluntarily moving the food bolus. The middle third is a mixture of striated and smooth muscle and at this point the voluntary act of swallowing is beginning to be taken over by involuntary control by the autonomic nervous system. The composition of the muscularis externa in the bottom third is all smooth muscle so that the food bolus is moved through that segment and into the stomach by the action of peristalsis - a wave like contraction controlled by the nerve plexi in the esophagus. The mucous glands secrete mucus into the lumen to lubricate the bolus of food thereby reducing the friction between the food and the epithelial lining of the esophagus.

hard palate histology

This is a section through the entire hard palate including the bone. The epithelium is parakaratinized and it has an extensive interlacing with the underlying lamina propria that is composed of dense connective tissue. The connective tissue is very dense here to provide a firm foundation for the epithelium. The mucosa is anchored into the bone via collagen bundles (arrow) that traverse the submucosa and insert into the bone of the hard palate. In this case this section was taken in the fatty area of the hard palate.

filtration membrane

This is a view at high magnification of part of a glomerulus and surrounding proximal convoluted tubules. First note the scale = 25 microns. Observe the erythrocytes in the capillaries of the glomerulus. Note the nucleus of an endothelial cell in one of the capillaries at the green arrow, and, a neutrophil in another capillary at the yellow arrow. Now note the urinary space that is labeled S. Next at the red arrow is a nucleus of one of the simple squamous epithelial cells that form the parietal layer of Bowman's capsule. Next observe the nucleus of a podocyte at the blue arrow. Podocytes form the visceral layer of Bowman's capsule. Finally, observe the very thin membrane that intervenes between the urinary space the lumen of a capillary at the black triangular arrow. This is the membrane that filters blood. Water, glucose, proteins and electrolytes, but not formed elements of the blood, pass from the capillary lumen to the urinary space across this membrane. Now we will look at this membrane in detail.

larynx

This is a view from the front of the body of a coronal section of the larynx. The section passes through the middle of the larynx. The epiglottis is at the top as indicated. The boxed in region is the location of the false (upper) and true (lower) vocal folds. If this boxed in area is viewed as a histological section it would appear as it does on the right. Note the glands associated with the false vocal fold (upper) and the vocalis muscle associated with the true vocal fold (lower). The surface of the false vocal fold is covered with pseudostratified ciliated columnar epithelium as illustrated on the right. The surface of the true vocal fold is covered with stratified squamous non-keratinized epithelium. This type of epithelium is commonly present where there is friction, or, in this case, the constant vibration of the epithelium with air passing over it.

digestion and absorption

This is a view of the mucosa of the small intestine and part of the submucosa. Villi and intestinal glands play critical roles in the absorption of glucose, lactose, fructose, amino acids and fatty acids. These two figures illustrate the process of breaking down glycogen and proteins into molecules that can be absorbed by the cells lining the small intestine. Glycogen digestion begins in the oral cavity with the amylase enzyme content of the saliva. Protein digestion begins in the stomach by the action of hydrochloric acid and pepsin. Lipids ingested in the form of triglycerides are acted upon by lipases secreted into the small intestine by the pancreas. As illustrated in this figure, triglycerides are broken down into monoglycerides (glycerol) and fatty acids. The fatty acids are bound to special carrier proteins that actively transport the fatty acids across the apical cell membrane of the absorptive cell. Once the fatty acids and monoglycerides are in the cytoplasm of the absorptive cell they are recombined into triglycerides unique to humans. The cell then coats the triglycerides in small amounts forming what are called chylomicrons that range from 1 - 3 microns in diameter. These pass out of the absorptive cell into the lamina propria where they go into lymphatic capillaries called lacteals. They are carried through increasingly larger lymphatics until they are emptied into the venous system. From there when they reach either the liver or adipose tissue the triglyceride is freed from its protein coat by lipoprotein lipase the trigylceride is taken up by liver cells or adipocytes. What you should recall from this slide is that sugars, proteins and lipids undergo their final digestion in the small intestine and they are taken into the body by the intestinal absorptive cells of the villi.

urinary tract

This lecture concludes with a presentation of the Urinary Tract. The urinary tract begins with the pelvis of the kidney. Urine flows from the pelvis into the paired ureters and then into the urinary bladder that stores urine until the bladder is full. Urine is then emptied via the urethra. The entire urinary tract is lined with a specialized epithelium consisting of several layers of cells the surface cells of which are dome shaped and have a special relationship between intracellular membrane vesicles and the cell membrane to provide a way for the epithelium to stretch without being torn.

pancreas

This low magnification survey view shows the islets of Langerhans, the endocrine portion (dark arrow heads), while the remaining parenchyma arranged as acini comprises the exocrine portion. The 2 small black arrows point to intralobular ducts which will drain into the much larger interlobular duct marked by the letter I. The asterisks note the arterial/venous drainage of the gland.

Intestinal Epithelial Cell Renewal

This scheme illustrates the life and renewal of the intestinal epithelial cells of the villus and the intestinal gland. All of the mitosis occurs in the population of cells in the wall of the intestinal gland, not at the base of the gland where Paneth cells reside. Observe how the new cells migrate up over the villus pushing older cells that undergo apoptosis and are shed at the tip of the villus. It only takes a maximum of 3 - 4 days for a new cell generated by mitosis from a stem cell in the intestinal gland to migrate to the tip and be shed. In other words the life of an intestinal epithelial cell that covers the villus is approximately 4 days. This is very important because these cells work very hard and wear out quickly.

alveolar septal elastic fibers

This slide demonstrates the presence of elastic fibers in the alveolar septa. Alveoli have the highest density of elastic fibers of any lung structure. Elastic fibers play a very important role in the compliance of the lung. Compliance is the property of the lung that allows it to expand when air is inhaled. The elastic fibers stretch to accommodate the increase in diameter of each of the several million alveoli so that the lungs can expand. Either through the aging process, but more than likely due to smoking, the population of elastic fibers is greatly reduced over time so that it becomes hard to inhale and exhale. Compliance allows that work to take place more efficiently. At the end of inspiration, they contribute significantly to moving air out of the lung by their elastic recoil. Emphysema destroys alveolar walls and elastic fibers thus reducing the aid of the elastic component in expiration making it very difficult to empty the lung of air in a normalbreathecycle. (Pulmonarycompliance (or lung compliance) can refer to either dynamic or static lung compliance. Static lung compliance is the change in volume for any given applied pressure. Dynamic lung compliance is the compliance of the lung at any given time during actual movement of air.)

alveoli and alveolar septa SEM

This slide illustrates alveoli and alveolar septa as they appear when viewed in a Scanning Electron Micrograph of a lung specimen. Specimens like this are prepared by freezing, then fracturing, then, freeze-dried, and coated with a metal and then viewed in the SEM. Several of the 300 million alveoli present in the lung are indicated along with several alveolar septae that form the walls of the alveoli. Note the capillaries in the alveolar septae as evidenced by the corrugated appearance.

nephron histology

This slide presents the types of cells that make up the wall of each of the segments of the nephron. Connecting to the renal corpuscle is the proximal convoluted tubule that is lined with simple cuboidal epithelium. The apical surface of each cell has microvilli that project into the lumen resembling a brush, thus called a 'brush border' making the apical surface of these cells look fuzzy at low magnification. The base of the cells shows striations that are a reflection of the many infoldings of the basal cell membrane with many mitochondria. Proximal tubule cells are very eosinophilic due to the large amount of intracellular membrane and mitochondria present. Distal convoluted tubule cells are shorter cuboidal cells than the proximal ones. The lumen border of these cells is very smooth because the distal tubule cells do not have microvilli projecting into the lumen, i.e. no 'brush border'. The cells of the loop of Henle are low cuboidal cells in the thick segment of the loop and very flat squamous cells lining the thin segment of the loop. The cells of the collecting duct are columnar forming a simple columnar epithelium. A unique feature of this epithelium is that you can see the borders or divisions between the cells. This is because the cells do not interdigitate laterally with each other in the collecting duct as they do in the proximal and distal tubules.

Kupffer Cell Distribution after intravascular injection of india ink

This slide shows a low and high magnification of a liver specimen taken from a rat that was injected with india ink intravenously. India ink is a suspensionofverysmallcarbonparticles. The carbon particles were phagocytized by von Kupffer cells. The nuclei of von Kupffer cells that are engorged with a foreign substance like carbon particles or bacteria etc. is usually obscured by the substance phagocytized. One von Kupffer cell in the right image indicated by the yellow arrow reveals a very small part of it nucleus (the light staining area). This demonstrates that Kupffer cells are quite numerous and it is easy to understand how effective they can be in taking bacteria and other undesirable components of the blood that may have entered into the portal venous system from the gastrointestinal tract.

Gall Bladder and common bile duct

This slide shows the location of the gallbladder and it intimate association with the liver. It is attached to the visceral surface of the liver. It is a blind pouch that stores, concentrates and releases bile into the duodenum. It receives dilute bile from the liver by way of the myriad of bile ducts that empty first into the hepatic duct and finally into a cystic duct that is connected to the gallbladder. When caused to do so by the action of smooth muscle in the wall of the gallbladder concentrated bile from the gallbladder is transported to the duodenum by the commonbileduct. Ahistologicalcross-section shows the wall of the gallbladder surrounded by liver tissue. The next slide will illustrate the gallbladder wall structure in detail.

Gall Bladder Epithelium Inactive Vs. Active absorption of water

This slide shows two electron micrographs of the simple columnar epithelium of the gallbladder. The left image shows the epithelium in its inactive phase. The right image shows the epithelium in its active phase. Observe the large spaces between the baso-lateral aspects of the lining cells where the long arrows are located. In order to concentrate bile, the lining epithelium actively pumps Na+ to the base where it passively draws water with it, thus concentrating the bile contents. The basa-lateral plasma membranes of these cells contain the active transport molecules that actively transport sodium and chlorid ions into the interstitium. Water follows passively. This results in concentrated bile stored in the gallbladder.

glomerular filtration membrane

This transmission electron microscope shows part of a glomerular capillary surrounded by the foot processes of a podocyte. Note the erythrocyte in the lumen of the capillary. The electron dense material in the lumen of the capillary is protein. The red arrow points at one of several fenestrations in the endothelium of the capillary. Foot processes are labeled (fp)....look in upper left of the image. Between each of the foot processes is a thin line (small arrows). This is a diaphragm or membrane that is attached to each foot process and extends between them. Now look between the endothelial cell and the podocyte foot processes and observe the basement membrane (B). The glomerular filtration membrane consists of 1) the fenestrated endothelial cell, 2) the basement membrane and 3) the podocyte foot processes and their diaphragms.

kidney inside view

Three distinct regions are recognized Cortex (C) Filtration Apparatus Tubules to process urine Medulla (M) -renal pyramids separated by renal columns of cortex Tubules & collecting ducts Pelvis (P) A basin or collection area for urine Each of the medulla regions are shaped like a pyramid. They are called medullary pyramids. Each medullary pyramid and the cortex associated with it makes up a kidney lobes. Here is one that is outlined. In this illustration there are 6 lobes. At the apex of a lobe (tip of the pyramid called the renal papilla) urine flows into the pelvis through a collecting funnel called a minor calyx (mc) The kidney histologically is classified as a solid organ that is organized into an outer cortex and inner medulla. It helps to think of the cortex of the kidney as a huge filter that is made up of nearly one million glomeruli (little rounded beds of capillaries), each having its own funnel collecting urine in as many tubules. Each funnel begins as an epithelial lined capsule called Bowman's capsule that surrounds the bed of capillaries. All of the glomeruli in Bowman's capsules are located exclusively in the cortex of the kidney. The tubules carrying the filtrate of blood that is the beginning of urine formation go through a tortuous path in the cortex, loop into the medulla, then back into the cortex to finally merge with collecting tubules, then collecting ducts. The collecting ducts converge in each lobe at the renal papilla (the apex of each lobe) as if a renal pyramid were a larger funnel. Urine finally is emptied into the renal pelvis from each renal medullary pyramid and the contents of the pelvis flow into the ureter.

transitional cell carcinoma

Transitional cell carcinoma (TCC, also urothelial cell carcinoma or UCC) is a type of cancer that typically occurs in the urinary system: the kidney and urinary bladder. It is the most common type of bladder cancer. TCC arises from the transitional epithelium, a tissue lining the inner surface of these hollow organs. In this low power view of a specimen from the bladder note the masses of cancer cells that have invaded into the underlying connective tissue indicating that this is a malignant carcinoma. Observe the concentration of lymphocytes nearby. These are most likely T-cells that are attempting to attack the cancer cells but most likely not that effective. Recall that T-cells are very mobile and attach cells directly that forms the basis of cellular immunity. When this boxed in area is viewed at higher magnification the cancer cells, T-cells and a patch of relatively normal transitional epithelium can be observed. Note the lymphocytes also in the blood vessel. Transitional cell carcinoma (TCC) can be very difficult to treat. Treatment for limited stage TCC is surgical resection of the tumor, but reoccurrence is common. Chemotherapy for TCC consists of the MVAC regimen (methotrexate, vinblastine, adriamycin and cisplatin). TCC can also be treated with infusions of BCG into the bladder. BCG stands for bacillus Calmette-Guerin solution. It contains weakened bacteria that stimulate the immune system to kill cancer cells in the bladder. This treatment is usually done once a week for six weeks. Side effects can include irritation of the bladder, an urgent need to urinate, and the need to urinate frequently. This is known as biological therapy because its mechanism is to recruit cells of the immune system (T-cells) to kill the cancer cell by cellular immunity.

cilia movement

Two longitudinal profiles are shown to illustrate the effect of the sliding of microtubules in a cilium. Note, in the power stroke, how the cilium bends. The diagram below shows the beating pattern of a cilium. There is a power stroke, positions 10 - 12 and a recovery stroke, positions 1 - 9.

urine

Urine is a sterile body liquid by-product secreted by kidneys, transported by ureters, stored in the urinary bladder and, excreted through the urethra through the act of urination Micturation is the process of eliminating liquid by-products of metabolism in the urine Urine is an aqueous solution of greater than 95% water, with the remaining constituents, in order of decreasing concentration urea 9.3 g/L, chloride 1.87 g/L, sodium 1.17 g/L, potassium 0.750 g/L, creatinine 0.670 g/L and other dissolved ions, inorganic and organic compounds. NASA contractor produced a 112 page report on composition of urine in 1971. Now, in the International Space Station, impurities are extracted from urine to make potable drinking water for the astronauts. http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19710023044_1971023044.pdf. See also: http://science.nasa.gov/science-news/science-at-nasa/2001/ast03apr_2/ Normal color of urine is pale yellow due to a by-product of the breakdown of aging Red Blood Cells. Dark yellow urine can be an indication of dehydration (urine is concentrated to conservationofwater). Colorlessurineisusuallybecauseofover-hydration,aconditionthat is considered healthier than dehydration. Wike Urine site: http://en.wikipedia.org/wiki/Urine Information is provided on this slide about urine and the process of eliminating it from the body in order for you to understand the nature of the function of the kidneys, the ureters, the urinary bladder and the urethra. Urine is a sterile liquid by- product of the body in the absence of disease that is secreted by the kidneys through a process called urination and excreted through the urethra. Secreted implies an active process and excreted implies a passive process. The overall process of eliminating liquid by-products of metabolism in the urine is known as micturition. Urine is 95% water with remaining constituents as listed on this slide that are essentially the by-products of metabolism and the elimination of ingested substances not needed by the body. An extensive 112 page report by a NASA contractor in 1971 preceding our space program implementing the practice of extracting impurities from urine to make potable drinking water for astronauts in the international space station. A link to the report is provided in this slide in case you are curious. Urine is pale yellow due to urobilin that is a final waste product formed as a result of the breakdown of heme from hemoglobin during the destruction of aging red blood cells. Dark yellow urine suggests a state of dehydration and light or colorless urine indicates a state of normal to over hydration (a healthy state). More detailed information about urine can be found at the Wiki link provided here in this slide.

Liver parenchymal cells

Viewed in the two dimensional plane the liver lobule appears as a plate. Within that plate the hepatocytes are arranged in cords which border the hepatic sinusoids. The hepatocytes are the most numerous of all of the cell types in the lobule. Hepatocytes have an intimate relationship with the sinusoids. The sinusoids are lined by endothelial cells. Blood flowing through the sinusoids comes from the nutrient rich low oxygen venous blood of the portal vein & oxygenated blood from the hepatic artery. Blood flows through the sinusoids into the central vein. Bile formed by the hepatocytes, drains in the opposite direction through special channels called canaliculi which drain into the bile duct by way of bile ductules (also calledHering's canal). Kupffer cells are macrophages (Mononuclear phagocytic system) located strategically within the sinusoids loosely attached to the endothelial cells. Their function is to ingest foreign materials such as any wayward bacteria which may have escaped from the GI lumen. They also serve to remove abnormal and aged rbc's after a splenectomy. The fat storing cells (cells of Ito) are responsible for the storage of vitamin A, a component in the synthesis of retinal pigments. They may also be responsible for most of the reticular fibers in the internal portion of the liver & would be involved in any fibrosis in response to a pathological condition. There is a gap between the hepatocytes and the lining of the sinusoids that is called the space of Disse that will be illustrated and explained in the next slide.

esophagus stomach junction

When viewed in the living state using an endoscope a transition in color at the esophagus-stomach junction can be observed. This endoscopic view obtained from the atlas at www.endoatlas.com is looking at the junction from the esophagus looking into the stomach. Observe the transition in color from whitish surface of the esophagus the red surface of the stomach. The border between the esophagus and stomach zig-zags and that is why it is named the Z line. In other words it is an interdigitating border. The stomach surface is red because the color of blood in the blood vessels is seen beneath the thin simple columnar epithelium. The esophagus whitish because the stratified squamous non-keratinized epithelium is so thick. In this opened esophagus as seen during an autopsy, the opaque whitish pink color of the esophagus changes abruptly at the stomach which is reddish. A histological section taken along the dotted line reveals this junction and confirms that it does change abruptly from the stratified squamous non- keratinized to simple columnar epithelium with mucosal glands.

kidney lobules and medullary rays

With an understanding of the blood vessels of the kidney, their relationship to the nephrons and the components of a nephron, you are prepared learn how a kidney lobe is organized. Each kidney lobe is subdivided into lobules. The lobules are organized around the collecting ducts that collect urine from the nephrons. So, where do these nephrons reside and how are they placed in the kidney lobules. This is a section of the kidney cortex. If the framed in area is enlarged two medullary rays will be seen. Observe the parallel profiles of longitudinal sections through collecting ducts and thick ascending/descending segments of the loops of Henle. Between the two medullary rays seen here is the cortical labyrinth of multiple cross-sections and oblique sections through the convoluted tubules among which are several glomeruli. Further enlargement as seen in the right image confirms the longitudinal profiles in the medullary ray and the sections through glomeruli and convoluted tubules on either side of the medullary ray. A medullary ray lies at the center of a kidney lobule and an interlobular artery lies between two adjacent lobules. The next slide will present a kidney lobule in more detail.