A&P 103B Mastering HW Digestive II

Case Study part P 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.

Case Study part J 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

Case Study part O 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.

Case Study part N 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.

Case Study part I 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.

Part B HCl secretions convert pepsinogen to the active hormone pepsin. What cells in the gastric pits produce pepsinogen? a) chief b) paracrine (also known as enteroendocrine cells) c) parietal d) G cells

a) Chief *Correct Yes, chief cells produce pepsinogen, the inactive form of pepsin

Part A Salivation is controlled almost entirely by the nervous system. Which of the following stimuli would inhibit salivation? a) nausea b) fear c) a lemon d) the thought of food

b) Fear *Yes, fear, sleep, fatigue, and dehydration all inhibit salivation.

Part A During which phase in the control of the digestive system would bicarbonate and bile be stimulated? a) cephalic phase b) intestinal phase c) gastric phase

b) Intestinal Phase *Yes, food in the intestines initiates a reflex that stimulates secretions of bicarbonate, digestive enzymes, and bile.

When proteins undergo deamination, the waste substance found in the urine is mostly________. a) ketone bodies b) urea c) ammonia d) acetyl CoA

b) urea

Gastrin, histamine, endorphins, serotonin, cholecystokinin, and somatostatin are hormones or paracrines that are released directly into the lamina propria. Which of the following cell types synthesize and secrete these products? a) mucous neck cells b) parietal cells c) zymogenic cells d) enteroendocrine cells

d) enteroendocrine cells

Case Study part R 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.

Case Study part K 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.)

Case Study part L 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.)

Case Study part M 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.

Case Study part Q 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.)

Match the following terms to their definitions. Glycolysis Gluconeogenesis Glycogenesis Glycogenolysis 1. Breakdown of glycogen to release glucose 2. Formation of glucose from proteins or fats 3. Storage of glucose in the form of glycogen 4. Break down of glucose to pyruvic acid

1. Breakdown of glycogen to release glucose - Glycogenolysis 2. Formation of glucose from proteins or fats -Gluconeogenesis 3. Storage of glucose in the form of glycogen -Glycogenesis 4. Break down of glucose to pyruvic acid -Glycolysis

Match the following. Secretin, gastric inhibitory peptide, gastrin, cholecystokinin 1. Stimulates insulin release and mildly inhibit HCl production. 2. Increases HCl secretion and stimulates contraction of intestinal muscle. 3. Increases output of enzymatic-rich pancreatic juice. 4. Increases output of pancreatic juice rich in bicarbonate ions.

1. Stimulates insulin release and mildly inhibit HCl production. - Gastric inhibitory peptide 2. Increases HCl secretion and stimulates contraction of intestinal muscle. - Gastrin 3. Increases output of enzymatic-rich pancreatic juice. -Cholecystokinin 4. Increases output of pancreatic juice rich in bicarbonate ions. -Secretin

Match the following terms to their definitions. ketogenesis lipolysis lipogenesis beta oxidation 1. Synthesis of lipids from glucose or amino acids 2. Splitting of triglycerides into glycerol and fatty acids. 3. Conversion of Fatty acids into acetyl groups 4. Formation of Ketone bodies

1. Synthesis of lipids from glucose or amino acids -Lipogenesis 2. Splitting of triglycerides into glycerol and fatty acids. -Lipolysis 3. Conversion of Fatty acids into acetyl groups -Beta Oxidation 4. Formation of Ketone bodies -Ketogenesis

Part B Norepinephrine is the neurotransmitter released by which fibers? a) sympathetic postganglionic fibers b) interneurons of the enteric nervous system c) parasympathetic postganglionic fibers d) both sympathetic and parasympathetic preganglionic fibers

a) Sympathetic postganlionic fibers *Yes, norepinephrine is the neurotransmitter of the sympathetic postganglionic fibers. An increase in the sympathetic system would decrease digestion.

Which enzymes are responsible for the final chemical breakdown of carbohydrates, proteins, and nucleic acids? a) brush border enzymes b) amylases c) pancreatic enzymes d) proteases

a) brush border enzymes

Which hormone causes an increased output of enzyme-rich pancreatic juice and stimulates gallbladder contraction to release bile? a) cholecystokinin b) gastric inhibitor peptide c) secretin d) gastrin

a) cholecystokinin

Which term describes the breakdown of stored fats into glycerol and fatty acids? a) lipolysis b) lipogenesis c) ketogenesis d) beta oxidation

a) lipolysis

Hepatocytes do not ________. a) produce digestive enzymes b) process nutrients c) detoxify toxic chemicals d) store fat-soluble vitamins

a) produce digestive enzymes

Part E Which of the following GI hormones promotes a pancreatic juice rich in bicarbonate ions? a) secretin b) GIP (gastric inhibitory peptide) c) gastrin d) motilin

a) secretin *Yes, secretin (from S cells in the duodenum) causes both the liver and pancreas to secrete bicarbonate into the small intestine

Case Study part D Dr. Lorraine explains to Mr. Volpe that H. pylori decreases the buffering effect in his duodenum. How does the duodenum buffer the acidic gastric chyme? a) Secretion of bicarbonate-rich mucosal mucus and pancreatic juice in the duodenum. b) Inhibition of acid secretion by the duodenum. c) Absorption of HCl by intestinal mucosal. d) Secretion of bicarbonate-rich gastric juice by the stomach mucosa.

a) secretion of bicarbonate-rich mucosal mucus and pancreatic juice in the duodenum *Normally, the pancreas secretes bicarbonate-rich "pancreatic juice" into the duodenum that matches the amount of HCl secreted in the stomach. In addition, the duodenal submucosal glands (called Brunner's glands) secrete an alkaline mucus. Together they buffer the acidity of gastric chyme.

Case Study part C Dr. Lorraine explains to Mr. Volpe that the H. pylori often causes excess stomach acid secretion. All of the following mechanisms normally increase gastric acid secretion EXCEPT ________. a) somatostatin b) histamine c) acetylcholine from the parasympathetic nerve fibers d) gastrin

a) somatostatin *Somatostatin inhibits gastric and pancreatic secretions.

Case study part B Dr. Lorraine is suspicious of a peptic ulcer, which is a disruption in the stomach or duodenal mucosa extending through its muscularis layer. The primary function of the mucosa is _________. a) to provide a protective barrier b) peristalisis c) segmentation. d) to anchor the stomach and duodenum to surrounding structures.

a) to provide a protective barrier *The mucosa is made up of simple columnar epithelium abundant in mucus-secreting cells which provide a slippery, wet protective barrier from digestive enzymes, pathogens, and other harmful substances. In both 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 epithelium is also simple columnar epithelium with abundant mucus cells; they produce an especially viscious, alkaline mucus that protects against the acidic gastric juices and pepsin. Additionally, there are deep gastric pits with a variety of chemical-secreting cells.

Transamination is the process whereby the amine group of an amino acid is ________. a) transferred to a keto acid b) transferred to acetyl CoA c) converted to urea d) converted to ammonia

a) transferred to a keto acid

Choose the incorrect statement regarding bile. a) Bile is both an excretory product and a digestive secretion. b) Bile contains enzymes for digestion. c) Bile functions to carry bilirubin formed from breakdown of worn-out RBCs. d) Bile functions to emulsify fats.

b) Bile contains enzymes for digestion.

Part D Which of the following intestinal hormones stimulates bile from the gall bladder? a) GIP (gastric inhibitory peptide) b) CCK (cholecystokinin) c) gastrin d) motilin

b) CCK (cholecystokinin) *Yes, CCK causes the gall bladder to contract, releasing bile and an enzyme-rich pancreatic juice to be secreted from the pancreas.

Case Study part G Mr. Volpe's epigastric pain, emanating from his duodenal ulcer, is relieved immediately by food, but returns 2-4 hours later. Which of the following explanations is most likely? a) Food is digested and absorbed in the duodenum within 2-4 hours of eating which causes pain. b) It takes 2-4 hours for the acidic chyme to move from the stomach into the duodenum. c) Food in the stomach causes the secretion of bicarbonate in the duodenum. d) After ingestion, food moves quickly into the duodenum protecting it from gastric acid for 2-4 hours.

b) It takes 2-4 hours for acidic chyme to move from the stomach into the duodenum *During the gastric phase, which begins when food enters the stomach, neural and hormonal signals cause parietal cells to secrete H+ and Cl-, dramatically increasing the production of HCl. At the same time, the pyloric sphincter is closed preventing HCl and chyme from leaking into the duodenum. The stomach typically takes 2-4 hours after ingestion to empty its acidic chyme into the duodenum. Also, food-mediated secretion of gastric HCl persists for 3-5 hours after eating. [Circadian-mediated secretion of HCl is maximal at night.] So, people with duodenal ulcers are likely to experience relief with ingestion of food, but pain 2-4 hours later, and at night.

Part C In response to a steak dinner, certain secretions are needed to aid digestion. What cells in the pancreas would provide these secretions? a) duct cells b) acinar cells c) islet of Langerhans cells

b) acinar cells *Yes, in response to a high fat and protein meal, CCK would be stimulated and in turn would stimulate an enzyme-rich secretion from the pancreas.

Case Study part A Mr. Volpe indicates he has epigastric pain, which leads Dr. Lorraine to consider several organs in that region. Which of the following organs is NOT a likely culprit since it is not in the epigastric region? a) liver b) appendix c) duodenum d) stomach

b) appendix *The epigastric region of the abdomen is above the umbilical region. The appendix is in the right-lower quadrant of the abdomen, below the umbilicus.

Part E The secretion in the large intestine consists of which of the following? a) intrinsic factor b) bicarbonate- and potassium-rich mucus c) bile d) digestive enzymes such as CCK and secretin

b) bicarbonate and potassium rich mucus *alkaline mucus secretion of bicarbonate and potassium protects the large intestinal wall from acids produced by resident bacteria

Case Study part H Mr. Volpe's one-year follow-up endoscopy shows a healed duodenal wall (no more ulcer). What distinctive feature is now visible in the duodenum? a) gastric pits b) brush border c) haustra d) rugae

b) brush border *The brush border is distinctive to the duodenum and is formed by the densely packed microvilli on the villi of the mucosal layer.

Which of the following is NOT a pathway in the oxidation of glucose? a) glycolysis b) gluconeogenesis c) electron transport chain and oxidative phosphorylation d) Krebs cycle

b) gluconeogenesis

One of the direct consequences of lactose intolerance is ______. a) increased intestinal absorption of this disaccharide b) increased osmotic pressure of the large intestine contents c) decreased motility of the small and large intestines d) increased blood glucose levels

b) increased osmotic pressure of the large intestine contents. *Osmotic pressure is the tendency of water to move into a cell by osmosis (diffusion of water). Recall that the rate of osmosis is dictated by the concentration of non-diffusible solutes in a solution.

What is a major function of pancreatic juice? a) acidifying the contents of the small intestine. b) neutralizing chyme entering the small intestine from the stomach. c) acidifying the contents of the stomach. d) emulsifying fats by breaking them into smaller pieces.

b) neutralizing chyme entering the small intestine from the stomach.

Case Study part F In Mr. Volpe's case, H. pylori degraded his duodenal lining, leaving it vulnerable to the stomach HCl. What other constituent of gastric juice is harmful to a damaged duodenal wall? a) mucus b) pepsin c) intrinsic factor d) bicarbonate

b) pepsin *Pepsin is an enzyme that digests protein in the acidic environment of the stomach. Typically pepsin is inactivated by the higher pH of the pancreatic juices in the duodenum. However, when H. pylori degrades the duodenal mucosa, the pepsin can further digest the tissue of the duodenal wall, creating an ulcer.

What triggers the release of secretin from the small intestine? a) presence of proteins in chyme entering the small intestine. b) presence of acidic, fatty chyme in the small intestine. c) presence of bile in the small intestine. d) presence of cholecystokinin (CCK) in the small intestine.

b) presence of acidic, fatty chyme in the small intestine.

Part C Enteric interneurons that are inhibitory to smooth muscle use which of the following neurotransmitters? a) norepinephrine b) substance P c) VIP (vasoactive intestinal peptide) d) ACh (acetylcholine)

c) VIP (vasoactive intestinal peptide) *Yes, both VIP and NO (nitric oxide) are inhibitory to smooth muscle.

How are most nutrients absorbed through the mucosa of the intestinal villa? a) facilitated diffusion b) bulk flow c) active transport driven directly or indirectly by metabolic energy d) simple diffusion

c) active transport driven directly or indirectly by metabolic energy

The function of the hepatic portal circulation is to ________. a) return glucose to the general circulation when blood sugar is low. b) carry toxins to the venous system for disposal through the urinary tract. c) collect absorbed nutrients for metabolic processing or storage. d) distribute hormones throughout the body.

c) collect absorbed nutrients for metabolic processing or storage.

How are fats absorbed into the blood? a) in the form of fatty acids and glycerol b) in the form of glycerol c) in the form of chylomicrons d) in the form of micelles

c) in the form of chylomicrons

Which of the following are mismatched? a) nuclease: DNA and RNA digestion b) lipase: fat digestion c) protease: lipid digestion d) amylase: carbohydrate digestion

c) protease: lipid digestion

Part D An increase in HCl (hydrochloric acid) secretion in the duodenum would stimulate which hormone that would help to counteract the effects of HCl? a) CCK (cholecystokinin) b) GIP (gastric inhibitory peptide) c) secretin d) gastrin

c) secretin *secretin stimulates the duct cells in the pancreas and liver to secrete a bicarbonate-rich solution that will bind hydrogen ions and increase the pH.

Which of the following is not an important function of the liver? a) protein metabolism b) synthesis of bile salts c) synthesis of vitamin K d) carbohydrate and lipid metabolism

c) synthesis of vitamin K

Case Study part E All of the following reasons can explain why most peptic ulcers, like Mr. Volpe's, occur in duodenum EXCEPT which statement? a) Bicarbonate-rich pancreatic juice is secreted after the acidic chyme enters the duodenum. b) The chyme coming from the stomach is very acidic. c) The duodenum is the anatomical structure nearest to the stomach's outlet. d) Normally, the duodenum lacks a mucosal layer.

d) Normally, the duodenum lacks a mucosal layer. *The duodenum is lined in a mucosa is made up of simple columnar epithelium abundant in mucus-secreting cells which provide a slippery, wet protective barrier from digestive enzymes, pathogens and other harmful substances. The duodenum is right at the outlet of the stomach, it is the first receptacle of stomach's highly acidic chyme, and the chyme arrives before the pancreas secretes neutralizing bicarbonate-rich juices.

Which cells of the small intestine secrete enterogastrones, such as secretin and cholecystokinin? a) absorptative cells b) goblet cells c) Paneth cells d) enteroendocrine cells

d) enteroendocrine cells

Gluconeogenesis is the process in which ________. a) glucose is converted into carbon dioxide and water b) glycogen is formed c) glycogen is broken down to release glucose d) glucose is formed from noncarbohydrate precursors

d) glucose is formed from noncarbohydrate precursors

Digestion of which of the following would be affected the most if the liver were severely damaged? a) proteins b) starches c) carbohydrates d) lipids

d) lipids