Physiology - An Illustrated Review
Questions & Answers
1. Most vagal preganglionic efferent nerves to the gastrointestinal (GI) tract synapse with
A. smooth muscle cells.
B. endocrine cells.
C. neurons in the myenteric plexus.
D. ganglia outside the GI tract.
E. exocrine glands.
2. Peristalsis is characterized by
A. intestinal smooth muscle contractions that are controlled by only extrinsic neural input.
B. contractions that proceed in an aboral direction down the gut for a distance of 1 to 2 ft.
C. contractions that can start only in the duodenum.
D. contractions that are prominent during fasting.
E. the gastrocolic reflex.
Questions 3 to 6 refer to the clinical scenario that follows. A 50-year-old female patient has symptoms that include heartburn, re-flux of blood, and waking up in the night coughing and choking with a mouthful of bitter-tasting fluid. She reports that this problem has been worsening over the past several months. Other symptoms noted by the patient are regurgitation of carbonated drinks, a persistent cough that is worse during the night, and recurrent substernal discomfort that can sometimes be relieved by over-the-counter (OTC) antacids. When asked, the patient reports being in generally good health for the past year, with no loss of appetite; her weight is unchanged relative to her last two annual checkups at her physician’s office.
3. What is the most likely cause of the patient’s symptoms?
A. Weakness of the cricothyroid muscle
B. Diffuse esophageal spasm
C. An incompetent lower esophageal sphincter (LES)
E. Nonulcer dyspepsia
4. Which procedure would be most helpful in determining the extent of reflux-induced damage to this patient’s esophageal mucosa?
B. Radiologic examination
C. Esophageal pressure measurement
D. Nuclear magnetic resonance (NMR) visualization of the lower esophagus
E. Ultrasonic visualization of the lower esophagus
5. Which treatment would be most helpful to the patient?
B. Reducing the intake of fatty foods
C. Administration of atropine
D. Administration of gastrin
E. A proton pump inhibitor
6. Under which of the following circumstances would this patient’s symptoms worsen?
A. During increased intragastric pressure
B. Following administration of secretin
C. Following administration of somatostatin
D. If the patient takes OTC antacids
E. If the patient is given metoclopramide to augment cholinergic neuroeffector transmission
7. Which condition would you expect to find in a patient after resection of the fundus and upper part of the corpus of the stomach?
A. Increase in the rate of slow-wave depolarizations
B. Increased secretion of pepsinogen
C. Decreased gastrin production
D. Failure of the stomach to empty
E. Loss of receptive relaxation of the stomach
8. You would expect gastric emptying to slow in response to
A. a high-fat meal.
B. elevated levels of motilin.
C. a high pH in the duodenal lumen.
D. an isotonic NaCl solution.
9. Stimulation of the parasympathetic nerves innervating the parotid glands causes
A. decreased concentration of HCO3− in saliva.
B. decreased O2consumption.
C. increased volume of secretion.
D. vasoconstriction in the parotid gland.
10. A patient with a duodenal ulcer is given a test meal, and the serum levels of several hormones are measured. The hormonal response to the test meal is repeated 24 hours after administration of the H+−K+ ATPase inhibitor omeprazole. The serum level of which of the following would be higher following drug treatment?
11. Which of the following substances when present in the duodenal lumen would produce the greatest stimulus for pancreatic exocrine secretion?
A. Lipid and glucose
B. K+ and HCO3−
C. Na+ and H+
D. Amino acids and Fe2+
E. H+and lipid
12. A 36-year-old male patient is about to be treated for Crohn disease by surgical removal of his terminal ileum. You are charged with explaining to the patient the nature of the postoperative complications he is likely to experience. Which of the following would you tell him to anticipate?
A. Reduced Ca2+ and Fe2+ absorption
B. Lowered serum cholesterol and pernicious anemia
C. Decreased hepatic bile salt synthesis and an increased risk of pancreatitis
D. Peripheral edema linked to protein malabsorption
E. Night blindness as a consequence of fat-soluble vitamin deficiency
13. In humans, which of the following would be an effective source of energy in the absence of exocrine pancreatic secretion?
14. When chyme first enters the duodenum, the direction of net flux of water is primarily determined by the
A. rate of Na+ absorption.
B. rate of organic solute absorption.
C. rate of Cl− absorption.
D. osmolarity of the chyme.
E. serum secretin concentration.
15. A patient had portions of his ileum and ascending colon removed after complications to repair an inguinal hernia. His subsequent steatorrhea and weight loss were treated with a low-fat, low-oxalate, and reduced lactose diet. What is the cause of his low serum Ca2+?
A. Increased Ca2+ secretion by the pancreas
B. Increased binding of Ca2+to the pancreatic enzymes
C. Increased binding of Ca2+to unabsorbed fatty acids
D. Increased binding of Ca2+to oxalate
E. Increased binding of Ca2+to unabsorbed proteins
Questions 16 and 17 refer the clinical scenario that follows.
A patient who has recently returned from an extended stay in a developing country develops a diarrhea that is characterized by the passage of a large volume of fluid, and he rapidly becomes dehydrated. Although the patient reports not eating for almost 48 hours, his diarrhea shows no signs of stopping, and although he has tried to increase his fluid intake, he continues to be severely dehydrated.
16. Which of the following is the most likely cause of this patient’s symptoms?
A. Celiac disease (sprue)
B. Irritable bowel syndrome (IBS)
C. Cholera enterotoxin
D. Ulcerative colitis
E. Crohn disease
17. Which of the following would be the most appropriate solution for oral rehydration of this patient?
A. Distilled water
B. Distilled water with glucose
C. Isotonic NaCl
D. A slightly hypotonic NaCl and glucose solution
E. An isotonic NaCl and glucose solution
Answers and Explanations
1. C. Most extrinsic nerves innervating the GI tract exert their effects via the myenteric plexus (p. 202).
A,B,D,E Very few efferents synapse directly on smooth muscle cells, endocrine cells, ganglia outside the GI tract, or exocrine glands.
2. B. Peristalsis moves a bolus a short distance along the gut in an aboral direction (p. 206).
A Peristalsis involves intrinsic but not extrinsic innervation of the gut.
C Peristalsis can start anywhere along the length of the small or large intestine.
D Migrating myoelectric complex (MMC) refers to those GI contractions that take place during fasting. Peristalsis are those contractions that occur in the GI in response to stretching of the gut wall, and is most important following gastric emptying.
E The gastrocolic reflex is characterized by increased colonic motor activity shortly after ingestion of a meal.
3. C. This patient is suffering from gastroesophageal reflux disease (GERD), and she is refluxing acidic gastric contents into her esophagus through an incompetent (partially open) LES. The “bitter taste” indicates the gastric origin of the refluxate because this shows it to be acidic. At this point, she is exhibiting symptoms consistent with erosive esophagitis (bleeding from the inflamed esophagus), suggesting that this is a long-standing problem (p. 207).
A The cricothyroid muscle supports the larynx, not the esophagus.
B Patients with diffuse esophageal spasm report excruciating pain during swallowing; this is a motility disorder that is not characterized by mucosal damage or regurgitation of the gastric contents into the mouth.
D Based on this patient’s general health, appetite, and weight, she is not nutritionally compromised, which indicates that food is passing from her esophagus to her stomach without difficulty. For this reason, and in the absence of any other likely related problems (e.g., aspiration pneumonia), a diagnosis of achalasia (failure of the LES to open) does not match her presenting symptoms. Although achalasia patients may report regurgitation, this refluxate does not have a “bitter taste” because it originates in the distal esophagus, not the acidic gastric lumen.
E Symptoms of nonulcer dyspepsia include abdominal discomfort, bloating, nausea, and early satiety. This is a functional bowel disorder that is not associated with pathophysiological damage to any structures in the upper GI tract. The presence of blood in this patient’s reflux precludes a diagnosis that is characterized by a lack of structural damage.
4. A. Endoscopy provides direct visualization of the mucosal surface.
B,D,E Radiology, NMR, and ultrasound all show the structure of the esophagus as a whole, but not the integrity of the mucosal epithelium.
C Pressure measurements may give an indication of altered motility linked to esophageal damage, but this tells us nothing quantitative about the mucosal surface itself.
5. E. A proton pump inhibitor will reduce the acidity of the gastric contents refluxing into the esophagus and allow mucosal healing to take place; these drugs are pharmacologically selective, essentially acting at only one anatomical location (parietal cells), and so would be the treatment of choice in this case (p. 207).
A Vagotomy will help to reduce acid secretion, but it is an invasive surgical procedure, and its effect on motility due to loss of receptive relaxation likely outweighs any potential benefits under these circumstances.
B Low-fat meals empty more rapidly from the stomach and provide a lesser stimulus for acid secretion, but this alone will not significantly alter the reflux of acid into the distal esophagus.
C Muscarinic cholinergic antagonists (atropine-like drugs) can also reduce acid secretion, but they are so nonselective in terms of where they act that the side effects would outweigh any benefits for this patient.
D Gastrin stimulates gastric acid secretion, which will make the patient’s condition worse. Note that this patient may benefit from a referral to have an assessment for a fundoplication to increase LES pressure.
6. A. Increased intragastric pressure increases reflux and would worsen the patient’s symptoms (p. 207).
B,C Secretin and somatostatin both reduce acid secretion and would lessen the patient’s symptoms.
D Antacids can provide symptomatic relief because they neutralize gastric acid in the distal esophagus and reduce the sensation of discomfort that causes.
E Metoclopramide is one of a class of drugs known as “prokinetic agents” because they directly or indirectly stimulate GI smooth muscle. In this case, the drug would augment LES tone and, along with an appropriate acid-reducing drug, help to reduce the reflux of acidic gastric contents into the distal esophagus, thus reducing the patient’s symptoms.
7. E. Receptive relaxation occurs in the proximal stomach (fundus and corpus), so this would be lost following resection (p. 208).
A Slow-wave depolarizations are not affected by the presence of the proximal stomach.
B Some pepsinogen is secreted by the proximal stomach, so secretion decreases.
C Gastrin is secreted in the distal stomach, so it is unaffected by this surgery.
D Stomach motility is reduced by this surgery, but the stomach still empties.
8. A. Lipid in the duodenal lumen inhibits gastric emptying via the enterogastric reflex (p. 209).
B Motilin has a promotility action on the stomach; for example, it plays an important controlling role in migrating myoelectric complex (MMC), powerful peristaltic contractions that remove non-digestible solids left behind in the stomach and small intestine.
C Gastric emptying is slowed by low pH in the duodenal lumen due to the presence of acidic chyme. The latter stimulates the release of secretin which slows gastric emptying by decreasing gastric motility and by increasing the tone of the pyloric sphincter. This is part of the hormonal mediation of the enterogastric reflex.
D As a consequence of the enterogastric reflex, isotonic NaCl empties more rapidly than solutions that are hyper- or hypotonic.
E Vagotomy causes the stomach to lose the ability to expand without contracting as the volume of the luminal contents increases (receptive relaxation); in the absence of this vagally mediated inhibition, gastric motility and rate of emptying are increased.
9. C. Parasympathetic efferent fibers stimulate salivation via muscarinic M3 receptors, resulting in increased volume of secretion (p. 215).
A The concentration of HCO3− in saliva increases as the rate of salivary secretion is increased.
B O2 consumption is increased by parasympathetic stimulation of the parotid gland.
D Parasympathetic stimulation causes the release of kallikrein, which activates bradykinin. Bradykinin is a potent vasodilator substance.
E Stimulation of the salivary glands via their parasympathetic inner-vation does not cause nausea, but nausea, as a prelude to vomiting, can be associated with increased salivary secretion.
10. A. Because accumulation of gastric acid in the antrum inhibits gastrin secretion via the release of somatostatin, gastrin levels increase when less acid is “pumped” into the stomach. This effect, however, will take time to manifest (p. 219).
B Secretion of cholecystokinin is not affected by changes in gastric acid production.
C Secretin release is stimulated by acid exiting the stomach and entering the duodenum, so its plasma concentration would be reduced in a patient taking a proton pump inhibitor such as omeprazole.
D Somatostatin is a paracrine substance, and although its release would be reduced if gastric acid production falls, it does not travel in the systemic circulation.
E Histamine secretion is stimulated by gastrin, so its levels increase, but it acts locally and does not change its concentration in blood.
11. E. Lipid in the duodenum stimulates secretion of the hormone cholecystokinin, and H+ stimulates the release of the hormone secretin. In combination, these hormones provide the largest stimulus for pancreatic exocrine secretion (pp. 224, 225).
A–C Glucose, K+, Na+, Fe2+, and HCO3− in the duodenal lumen do not affect the volume of pancreatic exocrine secretion either directly or indirectly.
D Amino acids only stimulate secretion of cholecystokinin, and Fe2+ does not affect the volume of pancreatic exocrine secretion.
12. B. Serum cholesterol decreases because it is used for hepatic synthesis of bile salts, and removal of the terminal ileum would interrupt the enterohepatic circulation by which this pool is returned to the liver from the small intestine. Vitamin B12(necessary for red blood cell formation) can only be absorbed in the terminal ileum. In its absence, absorption ceases, hepatic stores of this vitamin become depleted, and pernicious anemia follows (pp. 223, 253).
A Ca2+ and Fe2+ absorption occurs in the most proximal regions of the small intestine and would be unaffected by this surgical procedure.
C The reduction of the circulating bile salt pool would cause increased hepatic synthesis of bile salts, but there is no relationship between this phenomenon and the pancreas.
D Loss of the terminal ileum would not significantly change protein digestion or amino acid absorption, so a negative nitrogen balance and peripheral edema will not be a concern for this patient.
E Although this patient may initially experience diarrhea, lipid and therefore fat-soluble vitamin (A, D, K, and E) absorption is largely complete before the luminal contents reach the terminal ileum, so the patient is unlikely to experience night blindness as a consequence of long-term vitamin A malabsorption.
13. B. Sucrose can be digested by the brush border enzyme sucrase to produce one molecule of glucose and one molecule of fructose, each of which can be absorbed by the enterocyte and used for aden osine triphosphate (ATP) formation (p. 228).
A,D,E The other carbohydrates listed require a contribution from pancreatic amylase for digestion to occur.
C Cellulose is not digested to produce tri-, di-, or monosaccharides in the human small intestine, although this does occur in herbivores.
14. D. Chyme is initially adjusted to isotonicity by secretion (hypertonic chyme) or absorption (hypotonic chyme) of water. This process is facilitated by the “leaky” duodenal mucosa, which results from the large intercellular spaces in the epithelium (p. 235).
A–C After adjustment to isotonicity, absorption of water is dependent upon solute absorption.
E Secretin does not affect absorption of water.
15. C. Ca2+binds to free fatty acids more readily than to pancreatic enzymes, oxalate, or proteins (B,D,E).
A The pancreas does not secrete Ca2+.
16. C. The enterotoxin released by the bacterium Vibrio cholerae elicits uncontrolled intestinal secretion of Cl− via the cystic fibrosis trans-membrane conduction regulator (CFTR), and this draws massive quantities of water into the gut lumen. The fluid accumulating in the lumen by this mechanism stimulates motility, which in turn results in a decreased reabsorption time and extensive fluid loss from the body. Given the patient’s recent travel history, this option is the best match for his symptoms (p. 234).
A In celiac disease, the patient exhibits symptoms that are most likely to occur shortly after eating any gluten-containing food; this can be alleviated by diet modification. The continued presence of symptoms after a 48-hour fast should exclude this condition as a diagnosis.
B Patients with IBS may report, among other things, abdominal discomfort, bloating, gas, diarrhea and/or constipation, and/or a sensation of incomplete evacuation, but this condition is not associated with the severe dehydration and volume loss this patient is reporting.
D,E Ulcerative colitis and Crohn disease, collectively known as inflammatory bowel disease, are associated with abdominal pain and bloody diarrhea, but not normally extensive fluid loss and extreme dehydration, particularly the first time the patient presents, so these options do not correlate well with this patient’s symptoms.
17. D. Oral replacement therapy includes NaCl plus glucose. This works because substrate-coupled cotransport of glucose and sodium into the enterocyte via the Na+-dependent cotransport (SGLT1) is not disrupted by cholera toxin or the elevated intracellular cyclic adeno-sine monophosphate (cAMP) that it causes in intestinal epithelial cells; the inward movement of Na+ by this mechanism draws water out of the intestinal lumen and opposes the fluid loss associated with cholera toxin–induced hypersecretion of Cl− (pp. 233–235).
A Distilled water alone does not work because there is no net driving force that would take it out of the intestinal lumen and into the body, so the dehydration would just continue even if it were to be given.
B,C Na+ facilitates glucose absorption which serves as an energy (aden osine triphosphate [ATP]) source. NaCl is required to replace losses from the diarrhea.
E Slightly hypotonic is a better treatment than isotonic because this favors water absorption from the gut lumen.