Lippincott's Illustrated Q&A Review of Histology Ch 13 GI Tract

During your examination of the specimen described in Question 37, you are asked to discuss microfold (M) cells and mucosa-associated lymphoid tissue. What is the principal function of M cells in the distal ileum? (A) Antigen uptake (B) Fluid transport (C) Gastrin secretion (D) Histamine release (E) Chemoreception

The answer is A: Antigen uptake. The lamina propria of the GI tract contains large numbers of acute and chronic inflammatory cells. These cells form a diffuse mucosaassociated lymphoid tissue (MALT) that protects the body from pathogens. Macrophages and other phagocytic cells may penetrate the basal lamina and migrate into the lining epithelium to ingest pathogens. In the distal ileum, however, the process of delivering pathogens to lymphocytes cells is mediated primarily by microfold (M) cells. These phagocytic cells are found in the epithelium that covers Peyer patches. M cells are professional antigen-uptake and presenting cells, with apical membrane domains that are folded to provide greater surface area for sampling the luminal contents. Antigens taken up by M cells via pinocytosis and phagocytosis are processed and presented to lymphoid cells residing within cellular recesses. Keywords: Peyer patches, M cells

Your classmate opens a new digital slide and you study it together on the computer monitor. Identify the segment of the GI tract that is shown in the image. (A) Appendix (B) Duodenum (C) Ileum (D) Jejunum (E) Rectum

The answer is A: Appendix. This digital slide illustrates histologic features of the vermiform appendix. The appendix is a small, blind pouch that arises as a projection from the cecum. Aside from its small size, histologic features of the appendix are similar to those of the colon. The appendix exhibits a mucosa, submucosa, muscularis externa, and serosa/adventitia. A distinguishing feature of the appendix is the large number of secondary lymphatic nodules that extend into the submucosa (shown in the image). None of the other organs exhibit the distinctive histologic features of the appendix. Keywords: Large intestine, appendix

The visible mucus identified in Question 10 contains a high concentration of which of the following biomolecules? (A) Bicarbonate and potassium (B) Hydrochloric acid (C) Lysozyme (D) Polypeptide hormones (E) Proteases

The answer is A: Bicarbonate and potassium. The visible mucus that coats the gastric lumen is composed of heavily glycosylated proteins (mucins). In addition to mucins, surface mucous cells secrete bicarbonate ions and potassium. These molecules/minerals provide the mucus with an alkaline pH that serves to neutralize stomach acid near the lining epithelium. The other biomolecules are important components of gastric juice, but mucous cells do not produce them. Keywords: Stomach, cardiac glands

Various organs of the GI tract are examined in the histology laboratory. Identify the glandular structures located between the double arrows (shown in the image). (A) Brunner glands (B) Cardiac glands (C) Fundic glands (D) Intestinal glands (E) Pyloric glands

The answer is A: Brunner glands. The seromucinous glands in this slide specimen are located in submucosal connective tissue, external to the muscularis mucosae. These Brunner glands are a distinguishing feature of the proximal duodenum. Submucosal glands are also present in the esophagus (esophageal glands); however, unlike the esophagus, the mucosa shown in this image features intestinal villi lined by columnar epithelial cells (absorptive enterocytes). The open space observed between Brunner glands and the deeper muscularis externa is an artifact of paraffin embedding and sectioning. None of the other organs feature submucosal glands. Keywords: Small intestine, Brunner glands

You are analyzing patterns of stem cell renewal and terminal differentiation in the GI tract. As part of your research, you generate monoclonal antibodies that identify specific populations of gastric epithelial cells. One of your antibodies recognizes a protease found in zymogen granules. Which of the following cells is characterized by the presence of zymogen secretory granules? (A) Chief cells (B) Enteroendocrine cells (C) Mucous cells (D) Parietal cells (E) Plasma cells

The answer is A: Chief cells. Fundic glands (also called gastric glands) are composed of parietal cells, chief cells, mucous neck cells, enteroendocrine cells, and stem cells. Except for the cardiac and pyloric regions, these gastric glands are found throughout the stomach. Chief cells are typical protein-producing cells that feature an abundance of rough endoplasmic reticulum. These "protein factories" store pepsinogen (precursor enzyme) within intracellular zymogen secretory granules. Upon contact with gastric juice, pepsinogen is converted to pepsin—an aspartate protease. Pepsin was the first enzyme to be discovered in 1929 by John Northrup. Chief cells are located in deeper parts of the fundic glands. None of the other gastric cells store enzyme precursors in cytoplasmic zymogen granules. Keywords: Stomach, chief cells

For the autopsy specimen provided for Question 17, identify the basophilic cells clustered at the base of the gastric glands (lower right corner, shown in the image). (A) Chief cells (B) Enteroendocrine cells (C) Mucous cells (D) Paneth cells (E) Parietal cells

The answer is A: Chief cells. Pepsinogen-secreting chief cells are located at the base of the gastric glands. Pepsin (the active enzyme) cleaves proteins within the lumen of the stomach into peptides that are further degraded to amino acids in the small intestine. Pepsinogen (the pepsin precursor enzyme) is stored within zymogen granules in the apical cytoplasm of chief cells. As mentioned above, enteroendocrine cells would be difficult to identify without the use of special stains. None of the other cells are found in the fundus of branched tubular gastric glands. Keywords: Stomach, chief cells

After your lecture, a colleague asks you to comment on recent drug discovery efforts to regulate nutrient uptake in the small intestine. What hormone stimulates gallbladder contraction and pancreatic enzyme secretion? (A) Cholecystokinin (B) Gastrin (C) Ghrelin (D) Leptin (E) Secretin

The answer is A: Cholecystokinin. Pancreatic enzymes and bile salts enter the second part of the duodenum at the ampulla of Vater. Bile salts emulsify lipids, and pancreatic enzymes degrade lipids and carbohydrates. Contraction of the gallbladder to release bile salts is stimulated by cholecystokinin. This polypeptide hormone also stimulates exocrine cells of the pancreas to synthesize and secrete amylase and lipase. Enteroendocrine cells in the duodenum and jejunum secrete cholecystokinin. None of the other hormones regulate contraction of the gallbladder and/or secretion of pancreatic enzymes. Keywords: Enteroendocrine cells, cholecystokinin

During the seminar, you are asked to discuss the cellular mechanisms that mediate antibody transport across the epithelial barrier of the GI tract. Which of the following cells transports IgA from the lamina propria of the mucosa to the lumen of the gut? (A) Enterocytes (B) Goblet cells (C) Microfold cells (D) Paneth cells (E) Plasma cells

The answer is A: Enterocytes. Plasma cells release dimeric IgA (dIgA) into the interstitial fluid of the lamina propria. The antibodies are then bound by "polymeric immunoglobulin receptors" that are displayed along the basal membrane domain of enterocytes that line the mucosa of the small intestine. The dIgA-receptor complex is internalized and transported to the apical membrane of the enterocyte. Here, transmembrane immunoglobulin receptors undergo proteolytic cleavage to release secretory IgA (sIgA). Microfold (M) cells (choice C) internalize pathogens and present antigenic peptides to lymphocytes. They are found in Peyer patches in the distal ileum. None of the other cells transport dIgA from the lamina propria to the lumen of the gut. Keywords: Enterocytes, immunoglobulins, secretory IgA

The gastrointestinal (GI) tract is compartmentalized into organs that are specialized for digestion of food and absorption of nutrients. Most variation and specialization along the length of the GI tract occur in which of the following tissue layers? (A) Epithelium of mucosa (B) Lamina propria (C) Muscularis externa (D) Muscularis mucosae (E) Submucosa

The answer is A: Epithelium of mucosa. The GI tract is composed of four tissue layers: mucosa, submucosa, muscularis externa, and serosa/adventitia (depending on whether the organ is attached to other structures). The mucosa is subdivided into lining epithelium and underlying connective tissue (lamina propria and muscularis mucosae). Lining epithelial cells regulate specific functions of the GI tract, including (1) barrier to the entry of pathogens, (2) secretion of enzymes and hormones, and (3) absorption of nutrients, electrolytes, and water. The esophagus delivers food to the stomach, where it is formed into a semiliquid mass (chyme) and transported to the small intestine. Lipases and proteases degrade proteins and complex carbohydrates to amino acids and simple sugars, respectively. Bile salts stored in the gallbladder are added to emulsify lipids. Within the jejunum and ileum, nutrients and vitamins are transported across the lining epithelium, where they enter vascular and lymphatic vessels. The other layers of the GI tract exhibit regional variation, but epithelial cells of the mucosa exhibit the greatest range of differentiation. Keywords: Gastrointestinal tract, mucosa

Digital slides illustrating various organs of the GI tract are examined in the histology laboratory. The specimen shown in the image was obtained from which of the following anatomic locations? (A) Esophagogastric junction (B) Fundus of the stomach (C) Gastroduodenal junction (D) Ileocecal junction (E) Pylorus of the stomach

The answer is A: Esophagogastric junction. This slide specimen was obtained from the esophagogastric junction. Examination of the image reveals an abrupt transition from a nonkeratinized stratified squamous epithelium (on the right) to a mucinous columnar epithelium with gastric pits (on the left). Diffuse lymphatic tissue is noted in the submucosa at this junction. These lymphocytes are strategically located to detect and eliminate pathogens (immune surveillance). Fundus and pylorus of the stomach (choices B and E) feature gastric glands, but they do not reveal stratified squamous epithelium. The gastroduodenal junction (choice C) is characterized by the presence of submucosal Brunner glands. The ileocecal junction (choice D) does not exhibit a stratified squamous epithelium. The muscularis externa in this distal portion of the esophagus is composed of smooth muscle; however, the muscularis externa in the upper third of the esophagus is composed of striated skeletal muscle. Keywords: Stomach, esophagus, lymphatic tissue

A 2-year-old girl with a history of chronic constipation since birth is brought to the emergency room because of nausea and vomiting. Physical examination shows marked abdominal distension. Abdominal radiography reveals distended bowel loops. Which of the following developmental defects explains the pathogenesis of congenital megacolon in this patient? (A) Failure of neural crest migration (B) Hypertrophy of smooth muscle (C) Incomplete canalization of the primitive gut tube (D) Malrotation of the primitive gut tube (E) Persistence of the vitelline duct

The answer is A: Failure of neural crest migration. Congenital megacolon (Hirschsprung disease) results from a congenital defect in the innervation of the large intestine, usually the rectum. Severe chronic constipation is typical. Marked dilation of the colon occurs proximal to the stenotic rectum, with clinical signs of intestinal obstruction. Congenital megacolon is caused by defective colorectal innervation that prevents relaxation of sphincter muscles. Biopsy of the rectum showsdeficiency or absence of ganglion cells in the myenteric plexus. Ganglion cells of the autonomic nervous system are derived from neural crest cells. None of the other developmental anomalies are linked to the pathogenesis of Hirschsprung disease. Keywords: Hirschsprung disease, congenital megacolon

A 45-year-old man complains of difficulty swallowing and a tendency to regurgitate his food. Further studies demonstrate a complete absence of peristalsis and failure of the lower esophageal sphincter to relax upon swallowing. These clinicopathologic findings are explained as a deficiency (or absence) of which of the following structures in the distal esophagus? (A) Ganglion cells in the Auerbach plexus (B) Ganglion cells in the Meissner plexus (C) Presynaptic parasympathetic nerves (D) Presynaptic sympathetic nerves (E) Smooth muscle in the muscularis externa

The answer is A: Ganglion cells in the Auerbach plexus. Absence of peristalsis and failure of the lower esophageal sphincter to relax upon swallowing are referred to as achalasia. Achalasia is associated with depletion or absence of ganglion cells in the myenteric (Auerbach) plexus. Lack of parasympathetic innervation prevents relaxation of smooth muscle in the lower esophageal sphincter during swallowing. A myenteric plexus is shown in the image provided for Question 7 (oval, shown in the image). These structures are composed of peripheral nerves and ganglion cells of postsynaptic parasympathetic neurons. Meissner plexus (choice B) is found in the submucosa of the GI tract. None of the other structures are deficient or absent in patients with achalasia. Keywords: Achalasia, myenteric plexus

During a small group seminar, you are asked to discuss humeral immunity in the GI tract. Plasma cells in the lamina propria secrete primarily which of the following classes of immunoglobulin? (A) IgA (B) IgD (C) IgE (D) IgG (E) IgM

The answer is A: IgA. The mucosal surface of the GI tract is exposed to a wide variety of pathogens, including bacteria, viruses, parasites, and toxins. Tight junctions (zonula occludins) between the lateral borders of enterocytes provide a crucial barrier to the spread of infections. The mucosa is also protected by cellular and humeral (antibody-mediated) immunity. Whereas IgG is the most abundant immunoglobulin found in the blood, plasma cells in the lamina propria of the GI tract 188 Chapter 13 secrete primarily IgA. Dimeric IgA antibodies pass to the lumen of the gut. Here, secretory IgA (sIgA) crosslinks pathogens, masks pathogen adhesion molecules, and neutralizes toxins. Plasma cells in the respiratory and genitourinary system also secrete IgA. The other immunoglobulins (choices B, C, D, and E) mediate humoral immunity, but they are not secreted into the lumen of the GI tract. Keywords: Immunoglobulins, IgA

A 2-year-old boy is brought to the emergency room with a 48-hour history of nausea and abdominal discomfort. Physical examination reveals right lower quadrant guarding. Ultrasound examination of the abdomen reveals a 2-cm mass near the ileocecal junction. The child is discovered to have an obstruction caused by abnormal intestinal peristalsis. What is the appropriate pathologic diagnosis? (A) Intussusception (B) Meconium ileus (C) Stricture (D) Torsion (E) Volvulus

The answer is A: Intussusception. Obstruction in this child was most likely caused by "telescoping" of the small intestine related to abnormal peristalsis. This condition (intussusception) is usually a disorder of infants or young children and occurs without a known cause. In adults, the leading point of an intussusception is usually a lesion in the bowel wall, such as Meckel diverticulum or a tumor. In addition to acute intestinal obstruction, intussusception compresses the blood supply to the affected portion of the intestine, which may undergo infarction. Meconium ileus (choice B) is intestinal obstruction in neonates with cystic fibrosis. Volvulus (choice E) is an example of intestinal obstruction, in which a segment of the gut twists on its mesentery, kinking the bowel and interrupting its blood supply. None of the other choices are related to abnormal intestinal peristalsis. Keywords: Intussusception

Which of the following is an essential secretory product of the submucosal glands identified in Question 27? (A) Amylase (B) Bicarbonate ions (C) Hydrochloric acid (D) Lipase (E) Pepsinogen

The answer is B: Bicarbonate ions. Brunner glands secrete a bicarbonate-rich, alkaline mucus that neutralizes the acidity of gastric juice. In addition to protecting the lining of the small intestine, these alkaline secretions establish a neutral pH that is optimum for the activity of pancreatic enzymes that enter the second part of the duodenum. Exocrine cells of the pancreas secrete amylase and lipase (choices A and D). Parietal cells of the stomach secrete HCl (choice C). Gastric chief cells secrete pepsinogen (choice E). Keywords: Small intestine, Brunner glands

A 69-year-old woman undergoes a routine colonoscopy. During the procedure, a 2-cm mass is identified and resected. Microscopic examination shows irregular crypts lined by a pseudostratified epithelium. Normal tissue is evident at the tumor margin (shown in the image). In addition to mucin-producing goblet cells, these normal colonic glands are composed of which of the following epithelial cells? (A) Chief cells (B) Enterocytes (C) Enteroendocrine cells (D) Paneth cells (E) Parietal cells

The answer is B: Enterocytes. This photomicrograph shows the distinctive morphology of colonic glands in cross-section. The straight tubular glands are lined by enterocytes and goblet cells. The principal function of enterocytes in the colon is absorption of water and electrolytes. The lumens of the colonic glands are small and difficult to visualize. The glands are surrounded by loose connective tissue of the lamina propria. Enteroendocrine and Paneth cells (choices C and D) may be present in the colon, but these secretory cells are not common. None of the other cells are present in the large intestine. Tubular adenomas constitute twothirds of the benign colonic adenomas. Microscopically, tubular adenomas exhibit closely packed epithelial tubules, which may be uniform or irregular with excessive branching. Dysplasia and carcinoma often develop in tubular adenomas. As long as the dysplastic foci remain confined to the mucosa, the lesion is almost always cured by resection. Keywords: Adenomatous polyp, enterocytes, goblet cells

A 45-year-old man describes burning epigastric pain 2 to 3 hours after eating. Foods, antacids, and over-the-counter medications provide no relief, and prescribed inhibitors of acid secretion are only moderately effective. Endoscopy reveals multiple gastric and duodenal peptic ulcers. An abdominal CT scan reveals a pancreatic tumor. What polypeptide hormone is most likely secreted by this pancreatic islet cell neoplasm? (A) Cholecystokinin (B) Gastrin (C) Ghrelin (D) Motilin (E) Secretin

The answer is B: Gastrin. This patient shows evidence of Zollinger-Ellison syndrome. This syndrome is characterized by unrelenting peptic ulceration in the stomach and/or duodenum by the action of tumor-derived gastrin. Gastrin binds to receptors on parietal and chief cells to stimulate the production of gastric juice. Gastrin is secreted primarily by enteroendocrine cells in the stomach. However, for reasons that are unclear, gastrinproducing neuroendocrine tumors (gastrinomas) typically arise in pancreatic islets (microorgans composed of enteroendocrine cells). Among islet cell tumors, pancreatic gastrinomas are second in frequency only to insulinomas (insulin-producing tumors). None of the other polypeptide hormones stimulates gastric acid secretion. Keywords: Zollinger-Ellison syndrome, gastrinoma

A section of the jejunum described in Questions 31 and 32 is stained for carbohydrate using periodic acid-Schiff (PAS). Parallel arrays of intestinal villi are examined at high magnification (shown in the image). Identify the PAS-positive cells revealed in this tissue section. (A) Chief cells (B) Goblet cells (C) Histiocytes (D) Paneth cells (E) Parietal cells

The answer is B: Goblet cells. PAS identifies mucin-producing goblet cells in the intestinal villi (magenta cells, shown in the image). Mucins (heavily glycosylated glycoproteins) provide a protective coating over the lining epithelial cells and help lubricate the luminal contents. This photomicrograph reveals cytologic details of the lamina propria, including a beautiful example of a lacteal (arrowhead, shown in the image). These large lymphatic channels are lined by a simple squamous epithelium (endothelium). Paneth cells (choice D) are not found in the intestinal villi. Keywords: Small intestine, goblet cells

A 3-week-old boy is brought to the physician by his parents who report that he vomits forcefully immediately after nursing. Imaging studies reveal concentric enlargement of the pyloric canal. Which of the following best explains the pathogenesis of congenital pyloric stenosis in this infant? (A) Deviation of the septum transversum (B) Hypertrophy of smooth muscle (C) Incomplete canalization of the primitive gut tube (D) Malrotation of the primitive gut tube (E) Persistence of the vitelline duct

The answer is B: Hypertrophy of smooth muscle. Congenital pyloric stenosis is enlargement of the pyloric canal that obstructs the outlet of the stomach. This disorder is the most common indication for abdominal surgery in the first 6 months of life. Congenital pyloric stenosis has a familial tendency. The only consistent microscopic abnormality is hypertrophy of the circular muscle coat in the pyloric canal. Deviation of the septum transversum (choice A) causes congenital diaphragmatic hernia. Persistence of the embryonic vitelline duct (choice E) is known as Meckel diverticulum. None of the other congenital birth defects is associated with "projectile vomiting." Keywords: Stomach, congenital pyloric stenosis

Examination of the lamina propria of the organ identified in Question 3 reveals which of the following key histologic features of the GI tract? (A) Brunner glands (B) Lacteals (C) Meissner plexuses (D) Myenteric plexuses (E) Pyloric glands

The answer is B: Lacteals. The lamina propria of the mucosa is a loose connective tissue that supports the overlying epithelium. In the GI tract, the lamina propria provides adhesion molecules for attachment and migration of epithelial cells. It also provides space for vascular and lymphatic channels. In some regions of the GI tract, the lamina propria includes mucosal glands and lymphatic tissue. The lamina propria of the small intestine is characterized by the presence of large lymphatic channels, termed "lacteals." An example of a lacteal is evident in the image. These dilated lymphatic channels transport dietary lipids from the small intestine to the circulatory system, via the thoracic duct. Free fatty acids from the diet are taken up by enterocytes and converted to triglycerides. Triglycerides are combined with cholesterol and a carrier protein (apolipoprotein B48) to form chylomicrons. These macromolecules are secreted by enterocytes into the lamina propria, where they enter the lacteals for transport. Brunner glands (choice A) are submucosal glands in the proximal duodenum. None of the other structures are found in the lamina propria of the small intestine. Keywords: Small intestine, lacteals

An intestinal villus is examined at high magnification. Goblet cells appear to be secreting mucus into the lumen of the gut (arrows, shown in the image). Macrophages and lymphocytes visible in this slide specimen are located primarily within which of the following layers of the GI tract? (A) Epithelium of mucosa (B) Lamina propria (C) Muscularis externa (D) Muscularis mucosae (E) Submucosa

The answer is B: Lamina propria. The core of each intestinal villus is lined by an extension of the lamina propria. This loose connective tissue is composed of fibroblasts, smooth muscle cells, endothelial cells, lymphocytes, macrophages, and plasma cells. Contraction of smooth muscle fibers in the core of the villus stimulates the movement of lymph fluid within the lacteals. Macrophages are phagocytic cells derived from circulating blood monocytes. They ingest pathogens and present antigens to passing lymphocytes. Monocytes/macrophages and lymphocytes exit the blood from postcapillary (high endothelial) venules. None of the other layers of the GI tract occupy the core of the intestinal villi. Keywords: Mucosa-associated lymphoid tissue, lamina propria

A 68-year-old man undergoes surgery to remove a gastric adenocarcinoma. A portion of the proximal duodenum at the tumor margin is examined for evidence of malignant cells. Identify the structure within the oval (shown in the image). (A) Meissner plexus (B) Myenteric plexus (C) Peyer patch (D) Primary lymphoid nodule (E) Secondary lymphoid nodule

The answer is B: Myenteric plexus. This image shows ganglion cells embedded in loose connective tissue between the inner circular and outer longitudinal layers of the muscularis externa. These structures are termed the myenteric or Auerbach plexus. They contain the ganglion cells of postsynaptic neurons that innervate the muscularis externa. The Auerbach (myenteric) plexus facilitates the movement of food along the GI tract by regulating peristalsis. The Meissner nerve plexus (choice A) is located in the submucosa. Peyer patches (choice C) are aggregates of lymphoid tissue in the mucosa and submucosa of the distal ileum. Diffuse and nodular lymphoid nodules (choices D and E) are not common in the muscularis mucosae. Keywords: Myenteric plexus

A 68-year-old man with a history of intestinal malabsorption suffers a stroke and expires. Portions of the patient's small intestine are collected at autopsy, stained with H&E, and examined at low magnification. Identify the distinctive submucosal folds indicated by the arrows (shown in the image). (A) Haustra (B) Plicae circulares (C) Rugae (D) Teniae coli (E) Villi

The answer is B: Plicae circulares. This autopsy specimen was obtained from the jejunum. In this portion of the GI tract, the mucosa and submucosa are folded extensively to increase surface area for absorption. The submucosal folds (arrows, shown in the image) are referred to as plicae circulares. These folds/ridges extend partially around the lumen. Mucosal projections that cover the entire surface of the small intestine are referred to as villi (choice E). Intestinal villi are lined by a simple columnar epithelium with goblet cells. Haustra and teniae coli (choices A and D) are found in the large intestine. Rugae (choice C) are folds in the wall of the stomach. Keywords: Small intestine, jejunum, plicae circulares

A silver stain is used to identify enteroendocrine cells in the pyloric region of the stomach (small dark-stained cells, shown in the image). These argentaffin cells are classified as "open" or "closed" depending on whether or not their apical membranes reach the lumen of the gut. What is the primary function of "open" enteroendocrine cells in the GI tract? (A) Antibody secretion (B) Antigen uptake (C) Chemoreception (D) Gastrin secretion (E) Histamine release

The answer is C: Chemoreception. Enteroendocrine cells account for approximately 1% of epithelial cells in the GI tract. They develop from common enteric stem cells. Because of their similarity to secretory cells of the central nervous system, enteroendocrine cells are described as components of the diffuse neuroendocrine system. Most of these cells rest on the basal lamina, and their cytoplasm does not reach the lumen of the gut. These "closed" cells release hormones from their basal membranes into the underlying connective tissue. By contrast, "open" enteroendocrine cells have cytoplasmic extensions that reach the lumen of the gut. These cells express G protein- coupled chemoreceptors that continuously sample the contents of the gut and signal the release of hormones based on this chemical information. Keywords: Enteroendocrine cells, diffuse neuroendocrine system

The autopsy specimen described in Question 37 is examined at higher magnification. Identify the glandular structures located between the lines (shown in the image). (A) Brunner glands (B) Cardiac glands (C) Crypts of Lieberkühn (D) Fundic glands (E) Pyloric glands

The answer is C: Crypts of Lieberkühn. Histologic features of the small intestine include villi and mucosal glands. The intestinal glands are commonly referred to as "crypts of Lieberkühn." These simple tubular glands empty into the intestine at the base of the villi. Brunner glands (choice A) are submucosal glands in the proximal duodenum. Gastric glands (choices B, D, and E) are similar in appearance to intestinal glands (e.g., they are mucosalglands). However, the small intestine does not feature surface mucous cells or gastric pits. Keywords: Small intestine, intestinal glands

A 25-year-old woman suffers massive trauma and internal bleeding in a motorcycle accident and expires. The patient's visceral organs are examined at autopsy. Identify the segment of the GI tract shown in the image. (A) Cardia of the stomach (B) Esophagogastric junction (C) Fundus of the stomach (D) Gastroduodenal junction (E) Ileocecal junction

The answer is C: Fundus of the stomach. This image shows gastric glands emptying into the bottom of gastric pits. These fundic glands are populated largely by parietal cells in the neck of the gland and chief cells at the base of the gland. Parietal and chief cells are not present in cardiac and pyloric glands. Secretory cells of the gastric mucosa produce nearly 2 L of gastric juice per day. None of the other segments of the GI tract exhibit the distinctive histologic features of the fundus of the stomach. Keywords: Stomach, fundus

The organs identified in Question 9 are examined at higher magnification. Identify the structures indicated by the arrows (shown in the image). (A)Brunner glands (B) Cardiac glands (C) Gastric pits (D) Intestinal glands (E) Pyloric glands

The answer is C: Gastric pits. This image shows a thick layer of visible mucus (amorphous white debris) that is secreted by the surface mucous cells. These columnar epithelial cells are filled with mucinous granules that occupy most of the apical cytoplasm. The mucinous epithelium is interrupted by deep depressions, termed gastric pits (arrows, shown in the image). Visible mucus forms a gel-like coating that protects surface epithelial cells from the harmful effects of acidic gastric juice and mechanical abrasion. Cardiac glands (choice B) are present in the lamina propria. These glands produce a neutral pH mucus that is released into the bottom of the gastric pits. A small portion of the muscularis mucosae is visible on the lower right side of the image. None of the other glands are present at the esophagogastric junction. Keywords: Stomach, cardiac glands

You are invited to give a lecture on the pathobiology of enteroendocrine cells at a national conference on "childhood obesity" organized by First Lady Michelle Obama. During your lecture, you mention that enteroendocrine cells secrete a wide variety of polypeptide hormones. Which hormone produced in the stomach stimulates the perception of hunger? (A) Cholecystokinin (B) Gastrin (C) Ghrelin (D) Leptin (E) Secretin

The answer is C: Ghrelin. Appetite and the perception of hunger are stimulated by ghrelin, a 28-amino-acid (polypeptide) hormone that is secreted by enteroendocrine cells in the stomach and pancreas. Serum levels of ghrelin rise prior to a meal and decline following a meal. Ghrelin binds to receptors in the hypothalamus to stimulate appetite. Ghrelin receptors are found in many other organs, suggesting that this hormone has multiple functions in regulating growth and metabolism. None of the other hormones stimulate the perception of hunger. Keywords: Enteroendocrine cells, ghrelin

The internal organs of a 78-year-old woman who died of metastatic cancer are examined at low magnification. Identify the segment of the GI tract that is shown in the image. (A) Cecum (B) Duodenum (C) Ileum (D) Jejunum (E) Rectum

The answer is C: Ileum. This image reveals large aggregates of nodular lymphatic tissue that are referred to as Peyer patches. They are a characteristic feature of the ileum (particularly the distal ileum). The pale-staining regions within these lymphoid follicles represent areas of B-lymphocyte activation and proliferation. Peyer patches are located within the mucosa and the submucosa (i.e., they interrupt the muscularis mucosae). They participate in adaptive immunity and immune surveillance. Peyer patches are not present in the other segments of the GI tract. Keywords: Peyer patches, small intestine, ileum

Another of your monoclonal antibodies identifies proliferating stem cells in the gastric mucosa. You hope to use this antibody to isolate these progenitor cells using fluorescence-activated cell sorting (FACS). Which of the following locations in the mucosa provides a niche for multipotent gastric stem cells? (A) Fundus of glandular epithelium (B) Gastric pit (C) Isthmus of glandular epithelium (D) Lamina propria (E) Neck of glandular epithelium

The answer is C: Isthmus of glandular epithelium. Gastric glands are branched tubular glands that extend from the bottom of the gastric pit down to the muscularis mucosae. They are connected to gastric pits via a short segment that is referred to as the isthmus. A longer neck region (choice E) connects the isthmus to the fundus of the gland (choice A). Stem cell proliferation takes place in the isthmus. Cells destined to become mucous cells migrate up toward the gastric pits (choice B), whereas the other secretory cells (e.g., parietal and chief cells) move down toward the fundus (base) of the gland. Epithelial stem cells are not found in the lamina propria of the gastric mucosa (choice D). Fluorescence-activated cell sorting (FACS) provides a valuable tool for counting and sorting dissociated single cells based on the presence or absence of cell surface markers for which probes are available. Keywords: Stomach, stem cells

You are investigating the activation of smooth muscle in the muscularis mucosae of the stomach and its role in assisting outflow from gastric glands. The cell bodies for visceral motor fibers that innervate the muscularis mucosae are present in which of the following anatomic locations? (A) Auerbach plexus (B) Celiac ganglion (C) Meissner plexus (D) Nucleus ambiguous of the CNS (E) Sympathetic trunk

The answer is C: Meissner plexus. Visceral motor fibers that stimulate the mucosal glands and the muscularis mucosae filter through the Auerbach (myenteric) plexus (choice A) to form a secondary submucosal plexus, referred to as the Meissner plexus. This secondary plexus is difficult to identify on routine H&Estained slides, because the ganglion cells are sparse and the nerve fibers are delicate. Postsynaptic ganglion cells and nerve fibers that innervate the muscularis mucosae are not present in the other anatomic locations. Keywords: Meissner plexus

A 44-year-old woman presents with burning epigastric pain that usually occurs between meals. The pain can be relieved with antacids. The patient also reports a recent history of tarry stools. Gastroscopy reveals a bleeding mucosal defect in the antrum measuring 1.5 cm in diameter. Which of the following is the most likely underlying cause of peptic ulcer disease in this patient? (A) Alcohol abuse (B) Aspirin use (C) Emotional stress (D) Infection (E) Tumor

The answer is D: Infection. Peptic ulcer disease refers to breaks in the mucosa of the stomach and proximal duodenum that are produced by the action of acidic gastric juice. The pathogenesis of peptic ulcer disease is believed to involve an underlying chronic gastritis caused by Helicobacter pylori. This pathogen has been isolated from the gastric antrum of virtually all patients with duodenal ulcers and from about 75% of those with gastric ulcers. H. pylori gastritis is the most common type of gastritis in the United States and is characterized by chronic inflammation of the stomach. In addition to peptic ulcer disease, H. pylori gastritis is a risk factor for the development of gastric adenocarcinoma and gastric lymphoma. Eradication of H. pylori infection is curative of peptic ulcer disease in most patients. None of the other mechanisms of disease are linked to the pathogenesis of peptic ulcer disease. Keywords: Peptic ulcer disease

A 74-year-old woman complains of weakness and fatigue. She states that her stools have recently become black after taking a new nonsteroidal anti-inflammatory drug (NSAID). Gastroscopy reveals superficial, bleeding mucosal defects. What is the most likely mechanism for the development of acute erosive gastritis in this patient? (A) Activation of Hageman factor (B) Activation of serum kallikrein (C) Generation of membrane attack complex (D) Inhibition of cyclooxygenase (E) Mast cell degranulation

The answer is D: Inhibition of cyclooxygenase. Acute hemorrhagic gastritis is characterized by necrosis of the mucosa and is commonly associated with the intake of aspirin, other NSAIDs, or alcohol. Even small doses of aspirin or other NSAIDs can inhibit the production of regulatory prostaglandins in the stomach mucosa. Most NSAIDs work by inhibiting cyclooxygenase, an enzyme that generates prostaglandins from arachidonic acid precursor molecules. The factor common to all forms of acute hemorrhagic gastritis is breakdown of the mucosal barrier, which permits acid-induced injury. Mucosal injury causes bleeding from superficial erosions. Defects in the mucosa may extend into deeper tissues to form an Gastrointestinal Tract 185 ulcer. None of the other mechanisms of disease is associated with pathogenesis of acute erosive gastritis. Keywords: Gastritis, cyclooxygenase

Digital slides of the GI tract are examined in the histology laboratory. The double arrow (shown in the image) indicates which of the following layers of the large intestine? (A) Lamina propria (B) Muscularis mucosae (C) Mucosa (D) Muscularis externa (E) Submucosa

The answer is D: Muscularis externa. The layer of the GI tract indicated by the double arrow is the muscularis externa (also referred to as the muscularis propria). In the colon, the muscularis externa is composed of two layers: inner circular and outer longitudinal. As mentioned above, the outer longitudinal layer in the colon is condensed into three equally spaced bands referred to as teniae coli. A myenteric (Auerbach) plexus is present between the inner and outer layers of smooth muscle (arrowheads, shown in the image). Smooth muscle fibers in the GI tract are derived from the splanchnic mesoderm during development. None of the other layers of the GI tract exhibit the distinctive histologic features of the muscularis externa. Keywords: Gastrointestinal tract, muscularis externa

A 55-year-old man undergoes abdominal surgery to remove a neuroendocrine tumor (carcinoid) of the small intestine. Normal intestinal mucosa at the margin of the tumor is embedded in plastic, sectioned at 1.5 μm, and examined at high magnification. Identify the secretory cells within the box (shown in the image). (A) Enterocytes (B) Goblet cells (C) Macrophages (D) Paneth cells (E) Plasma cells

The answer is D: Paneth cells. These secretory cells clustered at the base of the intestinal glands are (in our opinion) among the most beautiful cells in the body. Their large secretory granules are intensely eosinophilic when stained with H&E. Paneth cells synthesize and secrete a variety of antibacterial substances, including lysozyme and defensin. Paneth cells help regulate the bacterial flora of the GI tract. None of the other cells exhibit the distinctive cytologic features of Paneth cells. Keywords: Small intestine, Paneth cells

During a clinical conference, you are asked to discuss physiological mechanisms that protect the stomach from the acidity of gastric juice and from mechanical abrasion. Which of the following small molecules plays an important role in maintaining bicarbonate secretion by surface mucous cells and increasing the thickness of the surface mucus layer in the stomach? (A) Histamine (B) Kinins (C) Nitric oxide (D) Prostaglandins (E) Serotonin

The answer is D: Prostaglandins. The physiologic gastric mucosal barrier is regulated by prostaglandins (e.g., PGE2). These hydrophobic signaling molecules are synthesized in the gastric mucosa. They play an important role in maintaining bicarbonate secretion by surface mucous cells and increasing the thickness of the surface mucus layer. Pharmacologic agents (nonsteroidal antiinflammatory drugs) that inhibit the formation of prostaglandins can compromise the gastric mucosal barrier, 184 Chapter 13 leading to acute erosive gastritis. Loss of the protective alkaline mucus layer enables acidic gastric juice to injure the mucosa, leading to necrosis and hemorrhage. None of the other small molecules regulates the physiologic gastric mucosal barrier. Keywords: Stomach, prostaglandins

A 61-year-old man undergoes routine colonoscopy. A small, raised, mucosal nodule measuring 0.4 cm in diameter is identified and resected. The surgical specimen is shown in the image. Microscopic examination reveals goblet cells and absorptive cells with exaggerated crypt architecture but no signs of nuclear atypia. This hyperplastic polyp was most likely removed from what region of the GI tract? (A) Ascending colon (B) Cecum (C) Descending colon (D) Rectum (E) Transverse colon

The answer is D: Rectum. Hyperplastic polyps are small, sessile mucosal growths that display exaggerated crypt architecture. They are the most common polypoid lesions of the colon and are particularly frequent in the rectum. They increase with age. The crypts of hyperplastic polyps are elongated and may exhibit cystic dilations. The epithelium is composed of goblet cells and absorptive cells, without dysplasia. Hyperplastic polyps are less common in the other anatomic locations. Keywords: Hyperplastic polyps

A 70-year-old man undergoes chemotherapy for liver cancer, develops sepsis, and dies of multiorgan system failure. The patient's visceral organs are examined at autopsy. The plastic-embedded section shown in the image was obtained from what segment of the GI tract? (A) Appendix (B) Esophagus (C) Large intestine (D) Small intestine (E) Stomach

The answer is D: Small intestine. This autopsy specimen was obtained from the small intestine (jejunum). Histologic features of intestinal mucosa include villi, enterocytes with microvilli, and mucus-secreting goblet cells. The small intestine is the principal site for nutrient absorption in the GI tract. The absorptive cells are referred to as enterocytes. These tall, columnar epithelial cells, with basal nuclei, express a variety of cell surface hydrolytic enzymes and transport proteins for uptake of amino acids, sugars, and lipids. Microvilli along the apical membrane domain of enterocytes increase the surface area of the small intestine by 600-fold. Intestinal glands in the appendix and large intestine (choices A and C) lack villi and microvilli. Gastric mucosa (choice E) features surface mucous cells and gastric pits. The esophagus (choice B) is lined by a nonkeratinized, stratified squamous epithelium. Keywords: Small intestine, villi

What cell surface glycoprotein found on M cells suggests that these phagocytic cells present antigens to lymphocytes in the GI tract? (A) CD4 (B) CD8 (C) IgM (D) MHC class I (E) MHC class II

The answer is E: MHC class II. M cells degrade pathogens within phagolysosomes. Peptides are bound by MHC class II molecules and transported to the cell surface. Foreign peptides presented by MHC class II molecules stimulate helper T cells to become activated. Once activated, T cells secrete a variety of cytokines that stimulate B-cell proliferation and differentiation. CD4 and CD8 (choices A and B) are antigen coreceptors on helper and killer T cells, respectively. IgM (choice C) is the antigen receptor on most B cells. MHC class I molecules (choice D) are present on the surface of nearly every cell in the body. These membrane glycoproteins provide targets for cell-mediated immunity (e.g., killing of virally-infected cells). Keywords: Peyer patches, M cells, major histocompatibility complex

Microscopic examination of the distal portion of the autopsy specimen provided for Question 5 reveals intestine- like glandular epithelium with goblet cells. These histopathologic findings are associated with which of following adaptations to chronic persistent cell injury? (A) Atrophy (B) Dysplasia (C) Hyperplasia (D) Hypertrophy (E) Metaplasia

The answer is E: Metaplasia. Adaptive responses to sublethal cell injury include atrophy, hypertrophy, hyperplasia, metaplasia, and dysplasia. Metaplasia is the conversion of one cell differentiation pathway to another. In this autopsy specimen, the normal stratified squamous epithelium of the esophagus (on the left) has been replaced by columnar epithelium with goblet cells (on the right) as a result of chronic injury. The distal esophagus is said to exhibit "intestinal metaplasia." This disorder (Barrett esophagus) typically occurs in the lower third of the esophagus. Complete intestinal metaplasia with Paneth cells Gastrointestinal Tract 183 and absorptive cells may also occur. Barrett esophagus is more resistant to peptic juice than normal squamous epithelium and appears to be an adaptive mechanism that serves to limit the harmful effects of acid reflux. None of the other cellular adaptations describe histopathologic findings in patients with Barrett esophagus. Keywords: Barrett esophagus, intestinal metaplasia

A 58-year-old woman with a history of indigestion after meals and "heartburn" presents with upper abdominal pain. She is currently being treated with proton pump inhibitors for gastroesophageal reflux disease (GERD). Which of the following types of epithelial cells has proton pumps and generates hydrochloric acid (HCl) within the lumen of the stomach? (A) Chief cells (B) Enterocytes (C) Goblet cells (D) Paneth cells (E) Parietal cells

The answer is E: Parietal cells. Gastric juice is produced primarily in the fundus and body of the stomach. It is composed of water and electrolytes, enzymes (e.g., pepsin), hormones (e.g., gastrin), intrinsic factor (essential for vitamin B12 absorption), mucus, and hydrochloric acid. Hydrochloric acid is generated by parietal cells in the fundic glands. Under the influence of gastrin, parietal cells produce hydrogen ions that are pumped into a complex set of membrane folds (intracellular canaliculi) by an H/K ATPase. Here, the hydrogen ions form HCl. None of the other cells produce HCl. Keywords: Stomach, parietal cells

The organ identified in Question 16 is examined at higher magnification (shown in the image). Name the round eosinophilic cells in these mucosal glands. (A) Chief cells (B) Enteroendocrine cells (C) Mucous cells (D) Paneth cells (E) Parietal cells

The answer is E: Parietal cells. Parietal cells are large, round eosinophilic cells with central nuclei. They have extensive intracellular membrane folds (canaliculi) that provide increased surface area for the hydrogen ion pumps (ATPases) that generate HCl. They also have an abundance of mitochondria, which provide ATP to fuel the pumps. Parietal cells are located primarily in the middle neck region of the fundic glands. Chief cells (choice A) are basophilic (not eosinophilic). Enteroendocrine cells (choice B) are present at every level of the gastric glands, but they would be difficult to identify without the use of special stains. Mucous cells (choice C) are characterized by the presence of secretory granules filled with whiteappearing mucins. Paneth cells (choice D) are found in the small intestine. Keywords: Stomach, parietal cells

A 34-year-old man presents with a 5-month history of weakness and fatigue. A peripheral blood smear shows megaloblastic anemia. Further laboratory studies demonstrate vitamin B12 deficiency. This patient's anemia is most likely caused by autoantibodies directed against which of the following GI cells? (A) Chief cells (B) Enteroendocrine cells (C) Microfold cells (D) Paneth cells (E) Parietal cells

The answer is E: Parietal cells. Pernicious anemia is an autoimmune disorder in which patients develop autoantibodies against parietal cells and intrinsic factor. Parietal cell antibodies lead to atrophic gastritis. Intrinsic factor is a glycoprotein that complexes with vitamin B12 in the stomach and facilitates its absorption in the small intestine (ileum). Deficiency of vitamin B12 results in megaloblastic anemia, a hematologic condition in which the peripheral blood smear shows macrocytosis of erythrocytes and hypersegmentation of neutrophils. Megaloblastic maturation (cellular enlargement with asynchronous maturation between the nucleus and cytoplasm) is noted in bone marrow precursors from all lineages. Paneth cells (choice D) are intestinal cells that secrete antibacterial proteins. None of the other cells secrete intrinsic factor. Keywords: Megaloblastic anemia, pernicious anemia

You are invited to shadow a GI pathologist. A surgical specimen is examined using a double-headed microscope. This normal tissue was obtained from which of the following locations in the GI tract? (A) Colorectal junction (B) Esophagogastric junction (C) Gastroduodenal junction (D) Ileocecal junction (E) Rectoanal junction

The answer is E: Rectoanal junction. This surgical specimen was obtained from the junction of the rectum and the anal canal. The image shows stratified squamous epithelium on the right and colonic epithelium on the left. Diffuse lymphatic tissue is noted at the junction of these segments. The stratified squamous epithelium of the anal canal becomes keratinized as it blends with skin on the external surface of the body. The esophagogastric junction (choice B) exhibits stratified squamous epithelium but does not show colonic glands. None of the other junctions feature colonic glands and stratified squamous epithelium. Keywords: Large intestine, rectum

During a small group discussion, you are asked to explain structural and functional differences between rugae, villi, microvilli, plicae circulares, teniae coli, and haustra. Rugae are found in which of the following segments of the GI tract? (A) Esophagus (B) Large intestine (C) Rectum/anal canal (D) Small intestine (E) Stomach

The answer is E: Stomach. Rugae are characteristic features of the stomach. These longitudinal folds (or ridges) enable the stomach to distend as it fills with food. Ménétrier disease (hyperplastic hypersecretory gastropathy) is an uncommon disorder of the stomach that is characterized by enlarged rugae. Plicae circulares, villi, and microvilli are elaborations of the mucosa or submucosa in the small intestine that increase the surface area for nutrient absorption. Teniae coli are longitudinal bands of smooth muscle in the colon that regulate segmentation and peristalsis. Haustra are large sacculations of the large intestine. None of the other segments of the GI tract exhibit rugae. Keywords: Stomach, rugae

Various GI organs are examined at a multiheaded microscope in the pathology department. The pathology resident asks you to comment on the glandular tissue located within the lines (shown in the image). These mucosal glands empty into which of the following segments of the GI tract? (A) Colon (B) Duodenum (C) Ileum (D) Jejunum (E) Stomach

The answer is E: Stomach. This autopsy specimen was taken from the pylorus of the stomach. The photomicrograph shows surface mucous cells, gastric pits, and mucosal glands. These pyloric glands secrete a neutral pH mucus that drains into the bottom of the gastric pits. None of the other organs feature gastric pits and mucous glands. Keywords: Stomach, pyloric glands

A 69-year-old man with a history of gastroesophageal reflux develops a pulmonary saddle embolus and expires. The patient's esophagus is examined at autopsy (shown in the image). Which of the following types of epithelium lines the proximal portion of this autopsy specimen? (A) Pseudostratified columnar with cilia and goblet cells (B) Pseudostratified columnar with goblet cells (C) Simple columnar with goblet cells (D) Stratified squamous, keratinized (E) Stratified squamous, nonkeratinized

The answer is E: Stratified squamous, nonkeratinized. The esophagus is a 25-cm tube that passes through the superior and inferior mediastinum. It enters the abdominal cavity at vertebral level T10 and delivers food to the stomach for mechanical and enzymatic digestion. This autopsy specimen was obtained from a patient with a history of chronic gastroesophageal (acid) reflux. It shows evidence of both normal (upper) and abnormal (lower) esophageal mucosa. The normal mucosa that lines the proximal portion of this esophagus (on the left) exhibits a nonkeratinized stratified squamous epithelium. Rugae are noted in the cardia of the stomach (on the right). None of the other types of lining epithelium describe histologic features of the esophagus. Keywords: Barrett esophagus, gastroesophageal reflux disease

The autopsy specimen described in Question 31 is examined at high magnification. Identify the delicate apical membrane feature indicated by the arrows (shown in the image). (A) Basal lamina (B) Glycocalyx (C) Lamina densa (D) Lamina propria (E) Striated brush border

The answer is E: Striated brush border. The intestinal epithelium is home to at least five different types of epithelial cells: enterocytes, goblet cells, Paneth cells, enteroendocrine cells, and microfold (M) cells. Enterocytes display thousands of delicate, apical membrane microvilli. These actin-filled membrane projections increase the surface area of the small intestine by 600-fold. They are recognized by light microscopy as a striated brush border (shown in the image). Microvilli are covered by a carbohydrate-rich glycocalyx (choice B) that protects the lining epithelium and provides a microenvironment for the display of membrane-bound hydrolytic enzymes. The glycocalyx cannot be identified on slides stained with H&E. Basal lamina, lamina densa, and lamina propria (choices A, C, and D) are extracellular matrix structures related to the basal membrane domain of epithelial cells. Keywords: Small intestine, striated brush border

Further examination of the specimen provided for Question 40 reveals arterioles and venules (arrows, shown in the image). These blood vessels are located within which of the following layers of the GI tract? (A) Adventitia (B) Lamina propria (C) Mucosa (D) Muscularis externa (E) Submucosa

The answer is E: Submucosa. The submucosa consists of dense, irregular connective tissue, as well as nerves, blood vessels, lymphatic channels, and glands (esophagus and duodenum). The submucosa provides a bridge between the mucosa and the muscularis externa. It also provides a pathway for nerves and vessels to enter/exit the various GI organs. None of the other tissue layers exhibit histologic features of the submucosa. Keywords: Small intestine, submucosa

Various organs of the GI tract are examined at low magnification in the histology laboratory. Identify the structure indicated by the arrow (shown in the image). (A) Adventitia (B) Haustra coli (C) Omental appendices (D) Plicae circulares (E) Teniae coli

The answer is E: Teniae coli. The large intestine includes the cecum, appendix, colon (ascending, transverse, descending, and sigmoid), rectum, and anal canal. This H&E-stained slide was obtained from the colon. The organ exhibits straight, tubular intestinal glands, as well as distinctive thickenings of the outer longitudinal layer of the muscularis externa. These bands of smooth muscle (three equally spaced bands) are referred to as teniae coli (arrow, shown in the image). These bands run longitudinally along the outer wall of the colon and are visible on gross inspection. Contractions of the teniae coli mediate segmentation and peristalsis, which serve to move the contents of the colon. Adventitia (choice A) is loose connective tissue associated with retroperitoneal visceral organs. Haustra coli (choice B) are sacculations on the external surface of the large intestine. Omental appendices (choice C) are fatty projections on the serosal surface of the colon. Plicae circulares (choice D) are submucosal folds in the small intestine. Keywords: Large intestine, teniae coli

A 76-year-old woman with a history of chronic infectious gastritis suffers a ruptured abdominal aortic aneurysm and expires. At autopsy, a silver stain of the patient's gastric mucosa reveals Helicobacter pylori (small curved rods, shown in the image). What bacterial enzyme allows these pathogens to survive in the acidic environment of the gastric lumen? (A) Chymotrypsin (B) Pepsin (C) Secretase (D) Streptokinase (E) Urease

The answer is E: Urease. Incidental findings are frequently encountered during an autopsy. In this case, a silver stain of the patient's gastric mucosa demonstrates H. pylori. These bacteria are adapted to survive in the acidic environment of the stomach. They have been shown to contain a large amount of urease. This enzyme hydrolyzes urea to generate an alkaline "ammonia cloud" that surrounds and protects the bacterium from the harmful effects of acidic gastric juice. None of the other enzymes contributes to the survival of H. pylori in the stomach. Keywords: Peptic ulcer disease, chronic infectious gastritis

A section of a normal distal esophagus is examined in the histology laboratory. Identify the layer of the GI tract indicated by the arrows (shown in the image).

The correct answer is D: Muscularis mucosae. Several layers of the GI tract are visible in this section of the esophagus, including lining epithelium, lamina propria, muscularis mucosae, submucosa, and muscularis externa. A myenteric nerve plexus is observed between inner circular and outer longitudinal layers of the muscularis externa (oval, shown in the image). The arrows shown in the image identify the muscularis mucosae. These smooth muscle fibers run in a longitudinal direction that is parallel to the overlying epithelium. Contraction of the muscularis mucosae generates ripples in the mucosa that facilitate the movement of food during swallowing. Mucosa (choice B) is the layer that includes surface epithelium, lamina propria, and muscularis mucosae. Submucosa (choice E) is the layer of dense irregular connective tissue that is located between the muscularis mucosae and the muscularis externa. None of the other layers of the GI tract exhibit the distinctive histologic features of the muscularis mucosae. Keywords: Esophagus, muscularis mucosae