COMSAE PHASE 1 GASTROINTESTINAL
PHYSIOLOGY PRACTICE EXAM WITH
ACTUAL QUESTIONS AND VERIFIED
ANSWERS, PLUS EXPLAINED
RATIONALES/EXPERT VERIFIED FOR
GUARANTEED 100% PASS 2026/LATEST
UPDATE/INSTANT DOWNLOAD PDF
Question 1
A 24-year-old medical student participates in a physiology experiment
examining gastric acid secretion. A researcher administers a drug that
directly stimulates the basolateral membrane of gastric parietal cells and
increases intracellular cAMP. Which intracellular event most directly
mediates the resulting increase in hydrochloric acid secretion?
A. Activation of protein kinase C by increased intracellular calcium
B. Insertion and activation of H⁺/K⁺-ATPase pumps into the apical
canalicular membrane
C. Activation of Na⁺/H⁺ exchangers on the basolateral membrane
D. Increased synthesis of intrinsic factor by chief cells
E. Opening of apical chloride channels secondary to decreased cAMP
Answer: B. Insertion and activation of H⁺/K⁺-ATPase pumps into
the apical canalicular membrane
Rationale: Gastric parietal cells secrete H⁺ through the apical H⁺/K⁺-
ATPase, which exchanges intracellular hydrogen ions for luminal
potassium. Histamine acting at H₂ receptors increases cAMP and
activates protein kinase A, promoting activation and insertion of
proton pumps into the secretory canalicular membrane. Acetylcholine
and gastrin primarily signal through increased intracellular Ca²⁺, but
all three major stimulants ultimately converge on the H⁺/K⁺-ATPase.
1
,Question 2
A patient with autoimmune destruction of gastric parietal cells develops
fatigue, glossitis, and macrocytic anemia. Laboratory studies
demonstrate antibodies against intrinsic factor. Which physiologic
process is most directly impaired?
A. Conversion of pepsinogen to pepsin
B. Digestion of triglycerides by pancreatic lipase
C. Absorption of vitamin B12 in the terminal ileum
D. Absorption of iron in the duodenum
E. Absorption of folate in the jejunum
Answer: C. Absorption of vitamin B12 in the terminal ileum
Rationale: Intrinsic factor is secreted by gastric parietal cells and
binds vitamin B12 after B12 is released from dietary proteins. The
intrinsic factor–B12 complex is absorbed by specific receptors in the
terminal ileum. Loss of intrinsic factor therefore produces vitamin B12
deficiency and megaloblastic anemia. Gastric acid facilitates protein
digestion and iron absorption but is not the direct mechanism
responsible for B12 uptake.
Question 3
A patient undergoes surgical resection of the terminal ileum because of
severe inflammatory bowel disease. Several months later, the patient
develops steatorrhea. Which physiologic mechanism best explains the
development of fat malabsorption?
A. Failure of pancreatic bicarbonate secretion
B. Loss of gastrin-producing cells
C. Impaired enterohepatic recycling of bile acids
2
,D. Failure of gastric lipase secretion
E. Increased hepatic synthesis of cholesterol
Answer: C. Impaired enterohepatic recycling of bile acids
Rationale: Most bile acids are actively reabsorbed in the terminal
ileum and returned to the liver through the portal circulation. Ileal
resection decreases the bile acid pool, reducing micelle formation and
impairing lipid absorption. Unabsorbed bile acids may also enter the
colon and cause secretory diarrhea. Pancreatic bicarbonate and lipase
are important for digestion but are not the primary problem caused by
terminal ileal resection.
Question 4
A healthy individual consumes a meal rich in carbohydrates. As chyme
enters the duodenum, pancreatic secretion increases substantially. Which
hormone is primarily responsible for stimulating pancreatic bicarbonate
secretion in response to acidic chyme?
A. Gastrin
B. Secretin
C. Cholecystokinin
D. Motilin
E. Somatostatin
Answer: B. Secretin
Rationale: Secretin is released from S cells in the duodenal mucosa
when acidic gastric chyme enters the duodenum. It stimulates
pancreatic ductal cells to secrete a bicarbonate-rich fluid that
neutralizes gastric acid. CCK primarily stimulates pancreatic enzyme
secretion and gallbladder contraction, whereas gastrin stimulates
gastric acid secretion.
3
, Question 5
A patient is given a fatty meal containing long-chain fatty acids. Which
gastrointestinal hormone is most strongly stimulated by the presence of
these nutrients and subsequently causes gallbladder contraction?
A. Secretin
B. Gastrin
C. Cholecystokinin
D. Somatostatin
E. Gastric inhibitory peptide only
Answer: C. Cholecystokinin
Rationale: CCK is secreted by I cells in the duodenum and jejunum in
response primarily to fatty acids and amino acids. It causes
gallbladder contraction, relaxes the sphincter of Oddi, stimulates
pancreatic enzyme secretion, and slows gastric emptying. These
actions optimize digestion of dietary fat and protein.
Question 6
A researcher administers atropine to a patient before a meal. Which
aspect of gastrointestinal physiology would be most directly reduced?
A. Histamine-mediated gastric acid secretion
B. Parasympathetic stimulation of gastrointestinal smooth muscle and
glands
C. Secretin release in response to duodenal acid
D. CCK release in response to fatty acids
E. Bile acid synthesis by hepatocytes
Answer: B. Parasympathetic stimulation of gastrointestinal smooth
muscle and glands
4
PHYSIOLOGY PRACTICE EXAM WITH
ACTUAL QUESTIONS AND VERIFIED
ANSWERS, PLUS EXPLAINED
RATIONALES/EXPERT VERIFIED FOR
GUARANTEED 100% PASS 2026/LATEST
UPDATE/INSTANT DOWNLOAD PDF
Question 1
A 24-year-old medical student participates in a physiology experiment
examining gastric acid secretion. A researcher administers a drug that
directly stimulates the basolateral membrane of gastric parietal cells and
increases intracellular cAMP. Which intracellular event most directly
mediates the resulting increase in hydrochloric acid secretion?
A. Activation of protein kinase C by increased intracellular calcium
B. Insertion and activation of H⁺/K⁺-ATPase pumps into the apical
canalicular membrane
C. Activation of Na⁺/H⁺ exchangers on the basolateral membrane
D. Increased synthesis of intrinsic factor by chief cells
E. Opening of apical chloride channels secondary to decreased cAMP
Answer: B. Insertion and activation of H⁺/K⁺-ATPase pumps into
the apical canalicular membrane
Rationale: Gastric parietal cells secrete H⁺ through the apical H⁺/K⁺-
ATPase, which exchanges intracellular hydrogen ions for luminal
potassium. Histamine acting at H₂ receptors increases cAMP and
activates protein kinase A, promoting activation and insertion of
proton pumps into the secretory canalicular membrane. Acetylcholine
and gastrin primarily signal through increased intracellular Ca²⁺, but
all three major stimulants ultimately converge on the H⁺/K⁺-ATPase.
1
,Question 2
A patient with autoimmune destruction of gastric parietal cells develops
fatigue, glossitis, and macrocytic anemia. Laboratory studies
demonstrate antibodies against intrinsic factor. Which physiologic
process is most directly impaired?
A. Conversion of pepsinogen to pepsin
B. Digestion of triglycerides by pancreatic lipase
C. Absorption of vitamin B12 in the terminal ileum
D. Absorption of iron in the duodenum
E. Absorption of folate in the jejunum
Answer: C. Absorption of vitamin B12 in the terminal ileum
Rationale: Intrinsic factor is secreted by gastric parietal cells and
binds vitamin B12 after B12 is released from dietary proteins. The
intrinsic factor–B12 complex is absorbed by specific receptors in the
terminal ileum. Loss of intrinsic factor therefore produces vitamin B12
deficiency and megaloblastic anemia. Gastric acid facilitates protein
digestion and iron absorption but is not the direct mechanism
responsible for B12 uptake.
Question 3
A patient undergoes surgical resection of the terminal ileum because of
severe inflammatory bowel disease. Several months later, the patient
develops steatorrhea. Which physiologic mechanism best explains the
development of fat malabsorption?
A. Failure of pancreatic bicarbonate secretion
B. Loss of gastrin-producing cells
C. Impaired enterohepatic recycling of bile acids
2
,D. Failure of gastric lipase secretion
E. Increased hepatic synthesis of cholesterol
Answer: C. Impaired enterohepatic recycling of bile acids
Rationale: Most bile acids are actively reabsorbed in the terminal
ileum and returned to the liver through the portal circulation. Ileal
resection decreases the bile acid pool, reducing micelle formation and
impairing lipid absorption. Unabsorbed bile acids may also enter the
colon and cause secretory diarrhea. Pancreatic bicarbonate and lipase
are important for digestion but are not the primary problem caused by
terminal ileal resection.
Question 4
A healthy individual consumes a meal rich in carbohydrates. As chyme
enters the duodenum, pancreatic secretion increases substantially. Which
hormone is primarily responsible for stimulating pancreatic bicarbonate
secretion in response to acidic chyme?
A. Gastrin
B. Secretin
C. Cholecystokinin
D. Motilin
E. Somatostatin
Answer: B. Secretin
Rationale: Secretin is released from S cells in the duodenal mucosa
when acidic gastric chyme enters the duodenum. It stimulates
pancreatic ductal cells to secrete a bicarbonate-rich fluid that
neutralizes gastric acid. CCK primarily stimulates pancreatic enzyme
secretion and gallbladder contraction, whereas gastrin stimulates
gastric acid secretion.
3
, Question 5
A patient is given a fatty meal containing long-chain fatty acids. Which
gastrointestinal hormone is most strongly stimulated by the presence of
these nutrients and subsequently causes gallbladder contraction?
A. Secretin
B. Gastrin
C. Cholecystokinin
D. Somatostatin
E. Gastric inhibitory peptide only
Answer: C. Cholecystokinin
Rationale: CCK is secreted by I cells in the duodenum and jejunum in
response primarily to fatty acids and amino acids. It causes
gallbladder contraction, relaxes the sphincter of Oddi, stimulates
pancreatic enzyme secretion, and slows gastric emptying. These
actions optimize digestion of dietary fat and protein.
Question 6
A researcher administers atropine to a patient before a meal. Which
aspect of gastrointestinal physiology would be most directly reduced?
A. Histamine-mediated gastric acid secretion
B. Parasympathetic stimulation of gastrointestinal smooth muscle and
glands
C. Secretin release in response to duodenal acid
D. CCK release in response to fatty acids
E. Bile acid synthesis by hepatocytes
Answer: B. Parasympathetic stimulation of gastrointestinal smooth
muscle and glands
4
