Answer Key to Short Answer Questions for
Answer Key to Short Answer Questions for
“Peptic Ulcer Disease: A Case on the Digestive System”
1. As Dr. Lorraine is listening to Mr. Volpe’s complaints she automatically visualizes the organs in the epigastric region that are the potential source of his problems. Where is the epigastric region and what organs associated with digestion are located in that area?
The organs near or in the epigastric region are the stomach, pancreas, liver, gall bladder, esophagus, and duodenum. The heart, aorta, and lungs are nearby but rarely refer pain to the epigastric region, and so rarely cause the gnawing, burning pain associated with eating that Mr. Volpe presents.
2. The structures in the epigastric region share a common nerve supply. Can you name the specific cranial nerve that serves this region and the part of the nervous system to which it belongs?
Cranial nerve X, the vagus nerve, carries visceral sensory information from receptors located in the abdominal organs.
3. In order to understand the disease in Mr. Volpe’s alimentary canal, one must know the layers that make up its walls. Design a chart that identifies the four basic layers of the alimentary canal, the tissues that make up each layer, and the general function of each layer.
The four layers of the alimentary canal, from the lumen out, are: mucosa, submucosa, muscularis externa, and serosa. The mucosa is coated with simple columnar epithelium. It secretes mucus, enzymes and hormone; protects underlying layers; and absorbs digested end-products. The submucosa, composed of areolar connective tissue, surrounds the mucosa and contains blood and lymph vessels as well as nerves that serve nearby tissues. The muscularis externa is composed of smooth muscle that contributes to motility in the alimentary canal. Lastly, the outermost serosa is an epithelial-connective tissue membrane (visceral peritoneum) that anchors the alimentary canal in the abdominal cavity. (In the esophagus, the serosa is replaced by a fibrous connective tissue called adventitia.)
4. Dr. Lorraine suspects a peptic ulcer. This is an inflammatory lesion in the stomach or duodenal mucosa, which may extend through all layers of the alimentary canal wall. Describe the basic histological (tissue) structure of the mucosa layer in the alimentary canal. Identify the unique features of the mucosa in the stomach and in the duodenum, and explain how this uniqueness determines the function of the stomach and the duodenum.
The mucosal layer is composed of three layers, beginning with the innermost layer: mucosa, lamina propria, and muscularis mucosae.
A basic mucosa is made up of simple columnar epithelium that is abundant in mucus-secreting cells, which provide a slippery, wet protective barrier from digestive enzymes, pathogens and other harmful substances. In both the stomach and duodenum, this epithelial layer is highly regenerative for rapid repair. This is particularly useful in the hostile environment of the stomach. In the stomach, the simple columnar epithelium contains many mucus cells; these cells produce a viscous, alkaline mucus that protects against the acidic gastric juices and pepsin. The stomach mucosa also forms gastric pits that release a variety of secretions, which form gastric juice. In the duodenum, the mucosa forms villi – finger-like projections that line the epithelium with microvilli; this greatly enhances surface area. Additionally, the duodenal mucosa forms deep, circular folds – plicae circularis – that churn chyme slowly along the duodenal wall. The greatly enhanced surface area and plicae circularis help to optimize nutrient absorption.
The lamina propria is made of loose aerolar connective tissue with a rich capillary bed. Along with the mucosa, the lamina propria forms what is called the mucus membrane. In both the stomach and duodenum, but particularly the duodenum, digested nutrients are absorbed into the capillaries.
The muscularis mucosae is made of a thin layer of smooth muscle. It contributes the movement of the mucosa and the facilitation of secretions in both the stomach and duodenum. (The muscularis externa is primarily responsible for motility patterns.)
5. Mr. Volpe asks, “What do the bacteria have to do with the ulcer?” Dr. Lorraine tells him that the H. pylori increases stomach acid secretion and, at the same time, breaks down the lining of your stomach and duodenum. What is the source and normal function of acid in the stomach and what regulates its production?
The parietal cells in gastric pits pump out hydrogen and chloride, which combine in the stomach to form the strong acid, HCl. HCl aids in digestion by activating pepsin, denaturing food proteins, and breaking down plant cell walls. As a protective mechanism, HCl kills many types of microorganisms. Secretion of HCl is under the regulation of the gastric reflex and the hormone gastrin. When food enters the stomach, baroreceptors are stretched and chemoreceptors detect protein and an increase in pH. Nerve signals reflexively increase gastric secretions (including gastrin) and motility. The protein content of food also stimulates the release of gastrin from enteroendocrine cells in gastric pits. Gastrin then stimulates the release of HCl from parietal cells.
6. Dr. Lorraine also explains to Mr. Volpe that H. pylori impairs the normal buffering effect in his duodenum. What does she mean by the “buffering effect?” How does the duodenum accomplish this, and in what way does this protect the duodenum?
Normally, when the acidic chyme is moved into the duodenum it signals the pancreas to secrete bicarbonate-rich juice into the duodenum and duodenal submucosal glands, and to secrete a mucus that is also rich in bicarbonate. The amount of the bicarbonate (a base) that is produced is approximately equivalent to the amount of HCl produced in the stomach. The protection this secretion offers is twofold: neutralization of the acidic chyme (raising the pH), and coating the duodenal wall in viscous, alkaline mucus. H. pylori diminishes the release of bicarbonate-rich mucus, leaving the intestinal wall vulnerable to erosion by the acidic chyme.
7. The medication Pepcid® that Mr. Volpe took for partial relief of his dyspepsia is called an H2 (histamine) receptor antagonist, or H2 blocker. That means it prevents histamine release. What is the normal function of histamine in the stomach and how might this help Mr. Volpe’s hyperacidity problem?
During the gastric phase of digestion, when food has entered the stomach, three chemicals are released that signal parietal cells to secrete HCl: acetylcholine (by parasympathetic nerve fibers), gastrin (by gastrin-secreting enteroendocrine cells called G cells), and histamine (from enterochromafin-like cells). A histamine-receptor blocker, like Pepsid® (famotadine), inhibits the release of histamine and, thereby, diminishes hydrogen generation and HCl secretion. Since histamine is the dominant pathway for hydrogen generation, blocking it is often sufficient to control acid secretion in the stomach.
8. H. pylori weakens the duodenal mucosa making it more susceptible to gastric juice. Besides the high acidity, why are the contents of gastric juice so hostile to the exposed duodenal wall?
Along with HCl, gastric juice contains pepsin, an enzyme that digests protein in the acidic environment of the stomach. Typically, pepsin is inactivated by the higher pH of the pancreatic juices. However, when excessive amounts of acid enter the duodenum and/or H. pylori degrades the duodenal mucosa, pepsin can further digest the tissue of the duodenal wall, creating an ulcer.
9. Why is Mr. Volpe’s dyspepsia relieved by food, and aggravated 2–4 hours after a meal?
When food enters the stomach (during the gastric phase of digestion) it raises the pH of stomach contents (which are less acidic), closes the pyloric sphincter, and inhibits duodenal secretions and motility. The stomach begins secreting HCl and is typically empty of food about 2-4 hours after a meal, longer if the meal is high in fat. Also, the stomach continues to secrete HCl for 3-5 hours after eating. (At night, circadian-mediated secretion of HCl is peaking, so this is why Mr. Volpe is awakened by the epigastric pain.)
10. One year after Mr. Volpe’s therapy, Dr. Lorraine performs a follow-up endoscopy and is delighted to see a healed and healthy duodenum. Describe what she sees through the lens of her endoscope as she looks at the lining of the duodenum.
The brush border is distinctive to the duodenum and is formed by the densely packed microvilli on the villi of the mucosal layer. The circular folds - plicae circularis - are also apparent.
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