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MCAT Digestive System Practice Questions: Enzymes, Absorption and Hormones

By StudyStore · Published 2026-11-04 · 8 original questions · about 12 min

Eight free MCAT-style practice questions on digestive enzymes, bile, pancreatic secretions, absorption in the small intestine and gut hormones, with explanations.

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Quick concept primer

Digestion starts in the mouth, where salivary amylase begins starch digestion. In the stomach, parietal cells secrete HCl and chief cells secrete pepsinogen, which is activated by acid to pepsin; pepsin digests protein at low pH. Gastrin stimulates acid secretion. In the duodenum, secretin signals the pancreas to release bicarbonate that neutralizes acid, and cholecystokinin (CCK) stimulates gallbladder contraction and pancreatic enzymes.

The pancreas releases amylase, lipase and proteases (trypsinogen, activated by enteropeptidase to trypsin). Bile, made in the liver and stored in the gallbladder, emulsifies fat but is not an enzyme. Most absorption occurs in the small intestine, where villi and microvilli increase surface area. Amino acids and glucose are absorbed into capillaries; fats are packaged into chylomicrons and enter lacteals. The large intestine reabsorbs water and ions.

8 practice questions

Try each question before opening the explanation. Click "Show answer and explanation" to check yourself. All questions are original and written for study practice.

Question 1

Which cells of the stomach secrete hydrochloric acid?

  1. Chief cells
  2. Goblet cells
  3. G cells
  4. Parietal cells
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Answer: D. Parietal cells

Parietal cells secrete HCl, and in humans also intrinsic factor needed for vitamin B12 absorption. Chief cells secrete pepsinogen, and G cells secrete the hormone gastrin.

Question 2

Why is pepsin secreted as the inactive precursor pepsinogen?

  1. It must be activated by a low pH, which prevents digestion of the cells that make it
  2. It is only active at basic pH
  3. It needs bile to become active
  4. It is a carbohydrate-digesting enzyme
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Answer: A. It must be activated by a low pH, which prevents digestion of the cells that make it

Storing pepsin as a zymogen protects chief cells from digesting their own proteins. Stomach acid converts pepsinogen to active pepsin, which works best at about pH 2. Pepsin digests proteins, not carbohydrates, and does not need bile.

Question 3

Which hormone released by the duodenum causes the pancreas to secrete bicarbonate to neutralize stomach acid?

  1. Gastrin
  2. Secretin
  3. Ghrelin
  4. Insulin
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Answer: B. Secretin

Acidic chyme in the duodenum stimulates S cells to release secretin, which prompts bicarbonate secretion from the pancreas. Neutralizing the acid allows pancreatic enzymes, which work at near neutral pH, to function. Gastrin acts on the stomach to increase acid secretion.

Question 4

Cholecystokinin (CCK) is released in response to fats and amino acids in the duodenum. Which effect does it have?

  1. Gallbladder contraction and release of pancreatic enzymes
  2. Increased gastric emptying
  3. Increased stomach acid secretion
  4. Conversion of trypsinogen to trypsin directly
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Answer: A. Gallbladder contraction and release of pancreatic enzymes

CCK stimulates the gallbladder to release bile and the pancreas to release digestive enzymes, and slows gastric emptying so the duodenum is not overloaded. Enteropeptidase, an enzyme of the duodenal brush border, activates trypsinogen.

Question 5

What is the main role of bile in digestion?

  1. Chemically cleaving triglycerides into fatty acids
  2. Digesting proteins in the duodenum
  3. Emulsifying fats to increase the surface area for lipase
  4. Neutralizing stomach acid with enzymes
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Answer: C. Emulsifying fats to increase the surface area for lipase

Bile salts are amphipathic and break large fat droplets into smaller micelles, which increases the surface area available to pancreatic lipase. Bile contains no digestive enzymes, and bicarbonate from the pancreas is mostly responsible for neutralization.

Question 6

After a meal, which statement about fat absorption is correct?

  1. Absorbed fats enter lacteals as chylomicrons
  2. Fatty acids enter the hepatic portal vein directly as free fatty acids in all cases
  3. Fats are absorbed in the stomach
  4. Fats are digested by salivary amylase
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Answer: A. Absorbed fats enter lacteals as chylomicrons

Within intestinal cells, monoglycerides and fatty acids are reassembled into triglycerides and packaged into chylomicrons, which enter lymphatic lacteals and later reach the blood. Glucose and amino acids instead enter capillaries leading to the hepatic portal vein.

Question 7

Which structure most directly increases the surface area for nutrient absorption in the small intestine?

  1. Goblet cells
  2. Villi and microvilli
  3. Peyer's patches
  4. The pyloric sphincter
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Answer: B. Villi and microvilli

Folds, villi and microvilli (the brush border) together create a very large absorptive surface. Goblet cells secrete mucus, Peyer's patches are lymphoid tissue for immune surveillance, and the pyloric sphincter controls passage from the stomach.

Question 8

A patient has a blockage of the pancreatic duct. Digestion of which nutrient would be affected most?

  1. Only simple sugars such as glucose
  2. Only water absorption
  3. Absorption of vitamin B12 in the stomach
  4. Fats, because pancreatic lipase would not reach the duodenum
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Answer: D. Fats, because pancreatic lipase would not reach the duodenum

The pancreas supplies most lipase, as well as amylase and proteases, so a blocked duct causes poor fat digestion and fatty stools. Simple sugars need no digestion, and vitamin B12 absorption depends on intrinsic factor from the stomach.

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Written by StudyStore from standard scientific facts as a study aid. These are not official exam questions and are not affiliated with or endorsed by any testing organization. Always check values against the reference provided with your exam or course.

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