BIO 405 Test 3

Know the location and secretions of the following regions of the human stomach: cardia pylorus body of the stomach

The cardia is a very small area at the junction of the esophagus. It contains mucus-secreting glands that lubricate food as it enters the stomach. The body of the stomach has the function of secreting acid-pepsin gastric juices as well as some protective mucus. The pylorus is the narrow region at the end of the stomach. It secretes mainly mucus to lubricate the passage of chyme into the duodenum.

Describe the blood flow through a liver lobule, including roles of hepatic arteries, hepatic portal veins, and central veins

The corners of the hexagon (arrows) contain portal tracts in which blood vessels are located. A large central vein (V) occupies the center of the lobule. Blood enters the lobule from the vessels at the corners, flows through sinusoids toward the center, and leaves the lobule via the central vein.

Describe the changes in cartilage, muscle and epithelium which occur along the bronchial tree (i.e., moving from the trachea, to bronchial tubes, to bronchioles).

The diameter of the bronchus is smaller,and the cartilage plates within the wall are discontinuous. The smooth muscle is more prominent and forms a spiral around the bronchus, and the bronchus is embedded within lung tissue.

Name the tissues of the trachea and give the function of each.

The enitre trachea is lined by a tall, respiratory epithelium supported by lamina propria (LP) and submucosa. However, the submucosa is thicker between rings and contains abundant glands that secrete a mixture of mucus and serous products. In sections containing a tracheal ring, the submucosa merges with the perichondrium of the hyaline cartilage.

Compare the exocrine and endocrine regions of the pancreas regarding both structure and function.

The exocrine pancreas is a large, compound gland; pancreatic acini secrete secrete digestive enzymes, and intercalated ducts secrete bicarbonate. The larger pancreatic ducts are supported by septa and resemble those of salivary glands. The endocrine pancreas consists of clumps of hormone-secreting cells surrounded by blood vessels; these islet cells secrete insulin and glucagon which regulate the glucose concentration of blood.

Define the term "bronchial tree" and list its major components.

The bronchial tree is a branching series of tubes that conduct air into the tissue of the lungs. The tree begins with the trachea which divides into two primary bronchi, one of which enters each of the two lungs. Within the lungs, the bronchi branch repeatedly resulting in bronchial tubes of ever decreasing diameter. The smallest bronchioles are too small to be seen with the naked eye. During Inhalation air is pulled through the bronchial tree, filling all of the airways.

List the functions of liver, gall bladder, and pancreas, including those functions not related to digestion.

A few of them are indicated here, just to give you an idea of the central role played by the liver in metabolism and homeostasis in addition to its role as a digestive organ. The liver has many important synthetic functions, such as production of proteins found in the blood. It also synthesizes glycogen from excess glucose for storage. If blood glucose levels drop, glucose is released from the liver. Another important liver function is removal of old or damaged erythrocytes from the bloodstream, a function shared by the spleen. But unlike the spleen, the liver reclaims iron from the erythrocyte hemoglobin and stores it for recycling. We do not usually think of the liver as an excretory organ, but it does excrete hemoglobin, excess cholesterol, and detoxification products through the bile duct. Thus, these waste products enter the intestine and are eliminated from the body with the feces. The detoxification functions of the liver are extremely important. It is breaks down toxic substances absorbed from food, which includes alcohol, before they can reach high enough levels to destroy other body tissues. Drugs, both legal and illegal, are also broken down within the liver. The gallbladder has an expandable wall and and a columnar epithelium that absorbs water. The exocrine pancreas is a large, compound gland; pancreatic acini secrete secrete digestive enzymes, and intercalated ducts secrete bicarbonate. The larger pancreatic ducts are supported by septa and resemble those of salivary glands. The endocrine pancreas consists of clumps of hormone-secreting cells surrounded by blood vessels; these islet cells secrete insulin and glucagon which regulate the glucose concentration of blood.

Describe the location within the liver and the specific function of: liver lobules sinusoids hepatocytes endothelial cells Kupffer cells lipocytes reticulin fibers portal tracts

All liver cells, called hepatocytes, are in direct contact with blood sinusoids. Sinusoids are supported by a reticulin network and are associated with Kupfer and lipocyte cells. Bile canaliculi are tiny channels between hapatocytes that collect bile. Liver lobules can be considered the functional units of the liver; a lobule contains portal tracts around the periphery and a central vein that drains the lobule. Portal tracts house small arteries, branches of the hepatic portal vein, and tiny bile ducts.

Explain the symptoms and cause of gingivitis.

Bacteria can easily breach the thin epithelium and enter the gingival tissue which then becomes inflamed.

Describe the embryonic origin of the liver, gall bladder, and pancreas.

Both the liver and pancreas develop as outgrowths from the gut tube. The liver appears first and grows rapidly. The pancreas originates from dorsal and ventral outgrowths. The gall bladder develops from the expanded tip of the original liver outgrowth which becomes the bile duct. Thus the hepatic ducts (leading into the liver) and the gall bladder are both attached to the bile duct. As development proceeds, the liver grows very large and the dorsal and ventral pancreas fuse to form a single organ.

Describe the major histological changes that occur in each of the following diseases of the respiratory system and indicate a potential cause : bronchitis pneumonia emphysema

Bronchitis results in a thickening of the bronchial walls, especially the muscle (M) and glandular (G) regions. In long-term (chronic) cases, the epithelium changes from pseudostratified columnar to stratified squamous in an attempt to protect the bronchial tissue from irritation and abrasion. Since this results in the loss of cilia, the copious mucus secreted by the enlarged glandular region cannot be moved up the bronchial tree by ciliary action. Coughing is then required to remove the mucus which is swallowed or spit out. Bronchitis can result from a viral or bacterial infection or from inhalation of chemicals. A common cause of bronchitis is smoking, since the particulate matter in smoke destroys cilia and irritates the bronchi. Pneumonia often begins as chronic bronchitis. Regardless of the initial cause of bronchitis, mucus accumulates within the small bronchial tubes and promotes growth of bacteria. In the lung tissue shown here, bronchioles have become filled with mucus and are infected with a pathogen. The infection has spread to alveoli which are also filled with mucus and pus. This material is thick and very difficult to cough up. It congests the infected portions of lung tissue which causes difficulty in breathing and ultimately may cause death. Emphysema is a condition in which the small airways and alveoli become expanded with an accompanying disruption of the alveolar walls. Since the elastin within the alveoli is disrupted, the elastic "scaffold" of the lungs is compromised. Consequently, the alveoli tend to collapse during expiration.

Describe the histological changes which occur during cirrhosis of the liver and indicate what might cause this condition.

Cirrhosis is a serious liver condition in which the hepatocytes deteriorate and are replaced by fibrous tissue. A common cause of cirrhosis of the liver is excessive alcohol consumption. Fibrous regions (F) extend from the portal tracts (P) and surround a lobule. Most hepatocytes within the lobule are swollen and/or deteriorating. No normal hepatocytes or sinusoids are present. This disruption of liver structure and accompanying death of hepatocytes results in reduced liver function and eventual liver failure.

Indicate the location of crypts and describe their role in epithelial turnover on the villi.

Crypts are located at the base of the mucosa. They open to the epithelial surface through tiny openings at the base of the villi. They migrate toward the villus tip and soon mature into functional enterocytes and goblet cells. When epithelial cells reach the villus tip, they die and are extruded. Thus the villus epithelium is continuously turning over, much like the epidermis of the skin

Draw a human tooth, label the following parts and give the functional significance of each: root crown pulp root canal dentine enamel

Dentine forms the roots of teeth and the most of the crown. Its matrix is similar to bone, but the cellular component differs. Enamel covers the outer surface of the crown. Like bone and dentine, it contains calcium crystals of hydroxyapatite, but the crystalline structure is denser. Enamel contains no cells and is the hardest of the skeletal tissues. The living tissue of teeth is found within the pulp, located with the center of the tooth. Teeth are held firmly within the jaw socket by cementum, another calcified tissue.

Compare (in general terms) the matrix of bone, dentine and enamel; which of this tissues lacks cells?

Dentine is produced by thin extensions of the odontoblasts. When the tooth is mature, these cellular processes remain as tiny, parallel tubes within the dentine (D). They are attache to the odontoblasts (labeled O) that remain when the tooth is mature and has erupted through the gum. The remainder of the dental papilla becomes the pulp of the tooth. The mature dentine is highly mineralized and harder than bone. While the remaining odontoblasts cannot repair or remodel the dentine, they do allow calcium to be added or removed from dentine during life. Thus teeth can participate in regulation of blood calcium levels, but to a lesser extent than bone. Enamel, unlike dentine, has no cellular component. The enamel organ is shed during tooth eruption and enamel is completely solid with no cellular covering. Its extreme hardness is designed to resist abrasion from chewing.

Describe symptoms and abnormalities in intestinal histology which occur during: diverticulitis benign polyps colon cancer (adenocarcinoma)

Diverticulitis: This abnormality of the colon is characterized by an ingrowth of the mucosa to form deep, thin pockets within the colon wall. Feces and bacteria may become trapped within these pockets leading to infection and inflammation of the colon. Polyps within the intestinal wall are common and increase in frequency with age. Some large polyps within the colon are seen in the photograph above. Genetic mutations during life cause the growth of polyps from the intestinal mucosa. A cancerous tumor (called an adenocarcinoma) is shown in the tissue section on the right. Compare the histology of this large tumor to the normal histology of the colon which is visible along the left edge of the section. The normal structure of the mucosa (M) and circular muscle (CM) has been completely disrupted by the tumor. Since the intestinal tissue is rich in capillaries and lymph vessels, malignant cells can easily enter these transport systems and spread cancer throughout the body.

Indicate the specific location and function of the following cell types: type I pneumocytes type II pneumocytes clara cells alveolar macrophages

Each alveolus is lined by a simple epithelium which contains two types of cells. Type I pneumocytes are long, squamous cells which provide the barrier between the interior of the alveolus and the surrounding capillaries. Type II pneumocytes are round with a large nucleus and represent 60% of the epithelial population. These cells secrete surfactant, a substance which reduces surface tension at the alveolar surface and prevents alveoli from collapsing during expiration. Capillaries are located between the epithelia of adjacent alveoli and are surrounded by thin fibers of connective tissue. Clara cells replace goblet cells in the epithelium of bronchioles. Alveolar macrophages wander through the lung tissue, removing inhaled particles and bacteria.

Regarding the development of teeth, Indicate the role of ectoderm and mesoderm, then describe the function of the following: dermal papilla enamel gland odontoblasts ameloblasts

Teeth have a dual embryonic origin. The dentine is produced by cells called odontoblasts. Like the osteoblasts and chondroblasts, they are derived from a mesodermal precursor cell. Fibroblasts also originate from mesoderm. Thus all cells that secrete the extracellular matrix of connective tissues develop from mesenchyme, the embryonic mesoderm. Enamel has a different origin: it is secreted by ameloblasts which are ectodermal cells. Thus teeth resemble skin in having an inner layer derived from mesoderm and an outer layer from ectoderm. The dental papilla will form the dentine and pulp of the developing tooth, while the enamel organ secretes enamel to cover the crown.

Describe the function and relationship to the nasal cavity of: sinuses turbinal bones olfactory epithelium respiratory epithelium

Each chamber of the nasal cavity is tall and long, but very narrow. Turbinal bones project from the sides of both chambers which increases their surface area These sinuses are cavities within the skull and thus are surrounded by bone. They serve as resonance chambers for speech and also reduce the weight of the skull. The sinuses are attached to the nasal cavities by narrow canals. The nasal mucosa consists of an epithelial layer supported by the lamina propria. Most of the human nasal cavity contains pseudostratified columnar epithelium. The majority of the epithelial cells are ciliated, but goblet cells (G) are also present. This type of epithelium is found throughout much of the respiratory system and is called "respiratory epithelium". The olfactory epithelium is responsible for sensing odors within the inhaled air. In humans, who have a poor sense of smell, the olfactory epithelium is localized to a small region of the nasal cavity.

Distinguish between the intercalated ducts and excretory ducts of the pancreas regarding location, structure and function.

Each intercalated duct drains the secretions of several acini Ducts merge throughout the pancreas and the largest ducts fuse with the main pancreatic duct which carries pancreatic secretions out of the organ.

1. Compare the structure and function of the epithelium in the esophagus, stomach, and small intestine. (Be sure to include glandular epithelium, if present).

Esophagus: Observe the stratified, squamous epithelium which is much like that of skin, but is not keratinized. This type of epithelium has a protective function. It is rare within the GI tract and found only in places where abrasion occurs. The lining epithelium of the stomach, and gastric pits is entirely made up of mucous columnar cells. These cells produce a thick coating of mucus, that protects the gastric mucosa from acid and enzymes in the lumen. In the small intestine, The villi are covered by a simple, columnar epithelium. Most of the epithelial cells are enterocytes which have a surface structure of microvilli. The microvilli are so small that an electron microscope is required to see them clearly.

Explain how, and why, the histology of the anal canal differs from that of the colon and rectum.

Especially note that the canal is lined with stratified, squamous epithelium similar to the epidermis of skin. Also note that the anal sphincter (which controls opening/closing of the anus) contains both smooth muscle and skeletal muscle. Hence, the anus is under a degree of voluntary control.

Explain how fat is absorbed and how it gets into the bloodstream; what are chylomicrons?

Fatty acids are absorbed into the intestinal epithelium by a non-specific, passive process. Essentially, they dissolve through the lipid portion of the microvillus membranes. Once within the enterocytes, fatty acids are reconstituted as fat molecules within tiny particles called chylomicrons. These lipid products diffuse into the central region of the villi and enter large lymph vessels called lacteals. Thus absorbed lipids are transported within the lymphatic system, whereas other nutrients immediately enter the blood stream.

Indicate the location of taste buds in the human tongue and indicate how their histological structure relates to function.

Fungiform papillae have taste buds (TB) located on their sides within the epithelial layer. A surface pore opens into the interior of the taste bud. Fluid containing the chemicals that generate taste enter through the pore and come into contact with neruro-epithelial cells. These sensory cells then generate a chemical-specific sensation which is conducted out the base of the taste bud by nerve fibers. The sensory signals travel to the brain which interprets them as taste.

List the digestive enzymes secreted by the pancreas and give the general function of each.

Lipase digests emulsified fat into fatty acids and glycerol, while amylase breaks down starch and glycogen into maltose (a disaccharide). The pancreas also secretes trypsin, which digests proteins into peptides. Trypsin is secreted in an inactive form, trypsinogen to avoid digestion of the pancreatic tissue. This inactive enzyme is activated within the duodenum by enterokinase, an enzyme secreted by the duodenal mucosa.

Distinguish between luminal digestion and membrane digestion; where does each occur and which nutrients are digested?

Luminal digestion, as the name implies, occurs within the lumen of the organ. As liquified food (chyme) leaves the stomach, it enters the duodenum and is mixed with secretions from the liver and pancreas. Note that both the bile duct from the liver and the pancreatic duct open into the duodenal lumen. The enzymes and other chemicals from these organs work within the lumen to digest fats, protein, and carbohydrates. This luminal digestion continues as the chyme passes into the jejunum and is usually completed before the ileum is reached. Although digestion begins in the stomach, the main result is the mechanical breakdown of food into chyme. The only enzyme secreted by the stomach is pepsin which begins the digestion of proteins. Some of these enzymes digest peptides to amino acids. Other enzymes digest maltose, sucrose, and lactose to simple sugars. Thus membrane digestion completes the digestion of proteins and carbohydrates, releasing the amino acids, glucose, and other simple sugars at the site where they will be absorbed.

Indicate where capillaries and lacteals are located within a villus; what role do they play in nutrient transport?

Most absorbed nutrients pass into the capillary beds within the villi. From there, they enter the hepatic portal vein and are carried to the liver. Capillaries (C) which lie just beneath the basement membrane. Once within the enterocytes, fatty acids are reconstituted as fat molecules within tiny particles called chylomicrons. These lipid products diffuse into the central region of the villi and enter large lymph vessels called lacteals.

Explain how the stomach is able to expand during a meal.

One of the stomach folds, a ruga, is present in the section. The submucosa, but not the muscular wall, extends into it. But note that the muscle layers are folded. This folded structure allows the stomach to expand to a considerable extent during a meal, then contract when digestion is complete.

Describe the cause and symptoms of coeliac disease.

Since surface area for digestion and absorption is greatly reduced, malnutrition results from this condition. Additionally, severe diarrhea and cramping usually occur. Coeliac disease results from an allergic reaction to gluten, a substance present in wheat and other grains. Eliminating wheat products from the diet results in the restoration of normal villi within the intestine.

2. Compare the the structure and function of the exocrine vs. endocrine pancreas. (Be sure to include both glandular tissue and ducts, if present).

The exocrine pancreas is composed of tightly packed acinar glands separated by thin strands of connective tissue. The acini are stained by two different methods in the tissue sections above. Each acinus is a ring of cells surrounding a tiny lumen (L). Pancreatic enzymes are secreted in the form of zymogen granules (ZG) which are visible within the cells stained pink. The enzymes are secreted into the lumen of the acini which connects to tiny intercalated ducts (D) that can be seen in longitudinal and cross section. The larger pancreatic ducts are supported by septa and resemble those of salivary glands. The endocrine pancreas consists of clumps of hormone-secreting cells, the islets of Langerhans, surrounded by blood vessels; these islet cells secrete insulin and glucagon which regulate the glucose concentration of blood.

Indicate how the histology of colon wall (muscle layers) differs from that of the small intestine.

The inner layer of circular muscle is thick, but the outer longitudinal layer is very thin in most places. Four bands of longitudinal muscle are thicker and are called the teniae coli.

Describe the interior of the mammalian tongue, regarding the type of muscle and glands present.

The inside of the tongue is mainly skeletal muscle. Observe the regions containing vertical and longitudinal muscle bundles. Since muscle fibers run in different directions, the tongue can be manipulated efficiently while chewing and swallowing food. The interior of the tongue contains numerous accessory salivary glands within the lamina propria (LP) and interspersed among the muscle bundles (M). Both serous glands (SG) and mucous glands (MG) are found throughout the tongue. They are derived from the epithelium and open to the surface by ducts. Like all accessory salivary glands, they produce a slow, continuous secretion of salvia (in this case to keep the tongue surface moist).

Indicate the location(s) of lymphoid tissue within the small intestine.

The lacteals within villi emerge from the intestine and merge to form increasingly larger lymph vessels. Several of these can be seen crossing the intestinal mesentery in the above photograph. Note that 3 lymph vessels enter a lymph node (LN) and a single large vessel emerges. The white color of these lymph vessels is due to the fat content of the lymph. Additionally, huge aggregates of lymphoid tissue, Peyer's patches, are found within the mucosa. Peyer's patches become more prominent in the distal regions of small intestine.

Indicate the two main hormones secreted by islet cells and give the general function of each.

The main cell type (called the beta cell) secretes insulin. This hormone stimulates most tissues (especially muscle and the liver) to take up glucose from the blood stream and influences a variety of metabolic functions. Other islet cells (called alpha cells) secrete glucagon which stimulates the liver to release glucose into the blood stream and has other metabolic actions opposite to those of insulin.

Describe the structure and function of a major salivary gland, including: septa lobules acini myoepithelial cells intercalated ducts striated ducts excretory ducts

The major salivary glands are so large that they are divided into functional units called lobules. Between the lobules are septa composed of connective tissue. The septa support blood vessels, nerves and the larger excretory ducts. The organization of a salivary gland into lobules (L) and septa (S) can be seen in this tissue. Each lobule contains tightly packed acini which are difficult to see at this low magnification. Excretory ducts (E) are recognizable in both longitudinal and cross section orientations. Note the tiny intercalated duct within the center of each acinus and the surrounding myoepithelial cells (M).

Know the location and function of the following structures within a gastric gland: gastric pit mucus cell parietal cell peptic cell neuroendocrine cell

The mucosa contains tubular, gastric glands that open to the surface as gastric pits; Parietal cells are unique in having intracellular channels called, canaliculi, that run deeply into the cytoplasm. Hydrogen ions are pumped from the cytoplasm into these canals. Chloride ions follow and the resulting hydrochloric acid moves out of the cell and into the lumen of the gastric gland. This acid, along with contractions of the stomach, initiates a chemical breakdown of food. The pH of stomach contents is between 2 and 4. The peptic cells secrete pepsin in the inactive form of pepsinogen. This protein accumulates in granules, and is secreted into the lumen of the gland by exocytosis. Once in the stomach lumen, the pepsinogen is converted into pepsin by the low pH. Pepsin is an enzyme which begins the digestion of protein. Neuroendocrine cells are found throughout the GI tract. They secrete hormones that regulate various aspects of digestion and gut motility. The neuroendocrine cells of the stomach secrete mainly gastrin which stimulates acid secretion by the parietal cells. Remember that endocrine glands, even if single-celled, secrete their products into the blood stream. Thus, the secretory granules of this cell are not near the lumen of the gastric gland, but accumulate at the opposite end of the cell, near the basement membrane.

Compare the structure of the esophagus and stomach regarding: epithelial type appearance of the mucosa general structure and function of glands types of muscle and location of muscle bands

The mucosa of the esophagus consists of the epithelium (E), lamina propria and muscularis mucosae (MM). The epithelium is stratified squamous for protection when food is swallowed. The lamina propria is very thin and difficult to see at this low magnification. Note the location of submucosa (SM) and muscle layers (CM and LM) which comprise most of the esophageal wall. Glands (G) are located within the submucosa. They are similar to seromucous salivary glands and secrete a liquid that lubricates the epithelial surface. A patch of lymphoid tissue (Ly) is also visible just beneath the mucosa. It is part of the MALT system and performs the usual immune-related functions. A thin connective tissue sheath, the adventitia, surrounds the esophagus, binding it to the surrounding connective tissue in this region of the body. The thick mucosa (M) contains parallel rows of tubular glands that extend to the muscularis mucosae (MM). The glands open to the surface via large gastric pits. The submucosa (SM) is also thick. Note the large blood vessels in this region. The stomach muscle is different from the rest of the GI tract in that its wall contains 3 muscle layers. In addition to the usual bands of longitudinal (L) and circular muscle (C), it has a third, interior band that runs obliquely (O). Acting together, these muscle bands allow the stomach to contract in all directions (not just peristalsis) which facilitates the digestive process.

Distinguish between the upper and lower respiratory systems.

The upper respiratory system is essentially the path that air follows from its entry through the nostrils to its passage through the glottis (the opening into the trachea).

Describe the muscle and mucosa of the gall bladder; what is the function of the epithelium?

The mucosa of the gall bladder is highly folded to form rugae similar to those of the stomach. These folds allow the gall bladder to expand when filled with bile. The mucosa contains a typical lamina propria (LP) composed of loose connective tissue with many elastin fibers and is covered by a simple columnar epithelium. The submucosa lies beneath the mucosa, but there is no muscularis mucosae. The smooth muscle consists of a single layer; its contraction expels bile from the gall bladder to the cystic duct and into the duodenum via the common bile duct.

Know the general structure of the GI tract as viewed in cross section, including the location and function(s) of: epithelium lamina propria muscluaris mucosae submucosa circular muscle smooth muscle adventitia (or serosa) autonomic ganglia

The muscular wall of the tract usually is divided into two layers: an inner layer where the fibers are oriented circumferentially (CM) and an outer layer in which fibers run longitudinally (LM). The alternate contraction and relaxation of these muscle bands is called peristalsis; it pushes the intestinal contents through the lumen in the direction of the anus. The mucosa contains an epithelial layer supported by the lamina propria (LP). A thin layer of additional muscle is located just below the mucosa. It is called the muscularis mucosae (MM) and separates the mucosa from the underlying submucosa (SM). The submucosa is composed of loose or dense connective tissue and contains the larger blood vessels, nerves, lymphoid tissues, and glands. The outer surface of the GI tract is covered by a connective tissue sheath which is called the adventitia when the tract is bound to adjacent structures or the serosa when the tract lies freely within the abdominal cavity. Note also the concentration of nervous tissue within the submucosa (submucosal plexus) and between muscle layers (myenteric plexus).

Describe the location and significance to lung function of: alveolar capillaries pulmonary elastic tissue lung pleura

The outer surface of the pleura is covered by a simple squamous epithelium called the mesothelium. The fibrous tissue of the pleura extends into the lung to form fibrous septa.

Name the 3 major salivary glands of humans and indicate the secretory products of each.

The parotid gland secretes serous products, whereas the sublingual gland produces mainly mucus; the submandibular gland secretes both products.

Indicate how a tooth is attached to the jaw socket, including the role of cementum and the periodontal membrane.

The roots of teeth are attached very tightly to bone within the sockets of the jaw. The periodontal membrane(PM) is very dense connective tissue with collagen fibers that extend into bone (B) on one side and into cementum (C) on the other. The cementum adheres to the dentine (D) of the root. The periodontal membrane thus fills the space between the bone and the tooth and provides a cushion during the force exerted by chewing. Although a tooth is held tightly within the jaw bone, it can move slightly to accommodate various pressures.

Describe the location and function of circular muscle, longitudinal muscle, and the muscularis mucosae.

The submucosa (SM) and muscularis mucosae (MM) are typical of those found throughout the GI tract, except that they are drawn into the plicae. Thus submucosal tissue forms the center of the plicae circularis and the muscularis mucosae underlies all of the villi. The intestinal wall contains the usual bands of circular and longitudinal muscle and is surrounded by the serosa.

Indicate the location and function of Brunner's glands.

The submucosa of the duodenum contains large glands called Brunner's glands. They produce a thin mucus that contains bicarbonate. this alkaline secretion neutralizes the acid contents of chyme as it emerges from the stomach.

Describe the mucosa and underlying tissues of the hard palate and lips.

The supporting connective tissue is called the lamina propria. It is loose near the epithelium and becomes denser deeper within the palate. The epithelium plus lamina propria is called the mucosa. These terms apply to the entire digestive tract, so now is a good time to learn them. The connective tissue beneath the mucosa is called the submucosa. It lies adjacent to the bone.

Describe the location and basic structure of the epiglottis and larynx.

The surface of the epiglottis (left micrograph) is covered by a stratified squamous epithelium which protects it from abrasion by food within the oropharynx. The epithelium is supported by a layer of dense connective tissue. The interior of the epiglottis (right micrograph) contains patches of elastic cartilage interspersed among regions of white adipose tissue. The larynx is formed by several pairs of cartilages which surround the upper end of the trachea. Dorsally, one pair of cartilages connects to the hyoid bone, a part of the skeleton.

Describe components of the biliary system, including the role of bile canaliculi, bile ducts within portal tracts, hepatic duct, cystic duct, and common bile duct.

The tiny bile canaliculi collect bile from individual hepatocytes and transport it to ductules which merge and lead into the bile ducts within the portal tracts of the liver lobules. This portion of the biliary system shown in green in the above diagram. The bile ducts of the portal tracts merge and eventually lead to the two large hepatic ducts which exit the liver.

Distinguish between terminal bronchioles and respiratory bronchioles.

The tiny terminal bronchioles (T) lead into respiratory bronchioles (R) as shown in the stained lung section above. Each respiratory bronchiole is surrounded by alveoli (A), the terminal units of the lung where gas exchange occurs. Terminal bronchioles have an intact wall and do not participate in gas exchange. In respiratory bronchioles, there are gaps in the wall; only patches of tissue containing muscle, collagen and elastin fibers (AR) support these bronchioles. Since the respiratory bronchioles have alveoli attached along their length, they do have a respiratory function.

Describe the mucosa of the mammalian tongue, regarding types of epithelium and papillae present.

The tongue is covered on all sides by stratified, squamous epithelium which is supported by connective tissue (the lamina propria). Note that the epithelium is much thicker on the upper surface of the tongue where most abrasion occurs. The largest are the circumvallate papillae which are found mainly near the back of the tongue. Fungiform papillae are smaller, but can be seen in the above image. Filiform papillae are the smallest and most numerous, covering most of the tongue surface. They are not visible at the magnification here. Note also that the posterior end of the tongue (the tongue root) is devoid of papillae.

Indicate the location of vocal cords and describe (in general terms) their structure and function.

The vocal cords are bands of connective tissue which are stretched across the the larynx just above the glottis. They are connected to the sides of the larynx by folds of tissue sometimes called the "false vocal cords". During inhalation, the vocal cords move apart to allow the entry of air into the trachea. During speech, the vocal cords move together and are stretched tight by small muscles and ligaments which move the laryngeal cartilages. When air is forced between the stretched vocal cords, they vibrate to produce a sound.

.Describe the structure and function of alveoli; what constitutes the air-blood barrier?

The walls of alveoli are very thin. Each alveolus is lined by a simple epithelium which contains two types of cells. The cytoplasm of the Type I cells and the endothelium of the capillaries form the blood-air barrier within the alveolar tissue. Note that pores within the epithelium allow communication between adjacent alveoli. This allows air pressure to equilibrate throughout the lung tissue.

Describe the location and function of microvilli in the small intestine

These cells have a dense layer of microvilli on the part of the cell that borders the intestinal lumen. The microvilli are collectively called the "brush border", a surface structure that can be seen in the electron micrograph of on the left.

Describe the general structure and function of the tubular glands within the colon; what cell types are present?

These glands contain dividing cells (stem cells) and are similar to the crypts of the small intestine. Most cells within the glands are goblet cells, but a few endocrine cells are also present. Note that most of the cells that line the luminal surface are absorptive cells. They absorb water and minerals, as well as fat-soluble products produced by bacterial activity within the lumen.

Explain the role of the following within the pharyngeal region: eustachian tubes tonsils (of several types) glottis epiglottis

These tonsils, along with those in the nasopharynx, guard the entrances to the eustachian tubes, trachea and esophagus. From the oropharynx, air passes through the glottis and into the trachea. The glottis is the opening into the trachea. When food is swallowed, the glottis is covered by the epiglottis, a flap of tissue supported by cartilage. In these illustrations, the glottis is open as it is during inhalation and exhalation.

Indicate the functions of the large intestine; what role due symbiotic bacteria play in human health?

They digest parts of food that the intestine cannot, such as fiber and certain carbohydrates. The main end product of this bacterial digestion is small fatty acids which then can be absorbed as nutrients. Bacteria also produce some essential vitamins, such as vitamin K, and aid the intestine in absorbing calcium and other minerals. Furthermore, the large number of beneficial bacteria prevent pathogenic species from growing in the intestine.

Compare the histology of the respiratory mucosa vs. olfactory mucosa regarding type of epithelium and types of glands present; which types are found in the nasopharynx?

This tissue section is from nasopharynx which, like the nasal cavity, is lined by respiratory epithelium (RE). While the mucosa of the nasopharynx does contain some mucus and serous glands, the dominant feature is lymphoid tissue. In this section, the entire lamina propria is packed with lymphocytes. Thus, the nasal mucosa functions to clean, warm, and humidify inhaled air before it passes into the lower respiratory system.

Explain the cause and symptoms of stomach ulcers; what is a perforated ulcer?

Ulcers form when the epithelial lining of the stomach is injured and there is insufficient mucus to protect the stomach tissues from acid. A perforated ulcer is life threatening; it is when the muscle wall of the stomach has eroded away, since bacteria within the chyme are now free within the main body cavity and will cause a massive infection there.

Describe the structure of an intestinal villus and indicate how its size and shape changes from the duodenum to the ileum; are villi present in the colon?

Within the duodenum (left SEM), villi are somewhat "leaf-shaped, broad in one plane. In the jejunum (right SEM) and the ileum, the villi become more cylindrical or "finger-shaped". The height of the villi also changes along the intestine. Villi are tallest in the duodenum, become progressively shorter in the jejunum and are shortest in the ileum. The large intestine has no villi.

Distinguish between accessory salivary glands and major salivary glands.

accessory salivary glands within the lining of the oral cavity and tongue. These are small, scattered glands with multiple, short, excretory ducts. The major salivary glands are the parotid, sublingual and submandibular which are large, compound glands. They are located outside of the oral cavity and secrete into the mouth by a single, large duct. The accessory glands secrete small amounts of saliva continuously under local control. In contrast, the major glands are controlled by the autonomic nervous system. They secrete large amounts of saliva when food is present in the mouth or due to other physical or psychological conditions.

Distinguish between the terms large intestine, colon, cecum and rectum.

intestine: cecum, colon, and rectum colon: the part of the large intestine that extends from the cecum to the rectum cecum: a pouch connected to the junction of the small and large intestines. rectum: the final section of the large intestine, terminating at the anus.

List all structures responsible for increasing the absorptive surface of the human small intestine.

the intestinal mucosa is folded transversely. These tightly packed folds are called the plicae circularis. They are visible to the naked eye. A second, much smaller, set of mucosal folds is found over the entire luminal surface, including the plicae circularis. These folds are called villi; they are typically finger-shaped and cannot be seen clearly without a microscope. The villi are covered by a simple, columnar epithelium. Most of the epithelial cells are enterocytes which have a surface structure of microvilli.