Gastrointestinal Secretion, Digestion and Absorption Quiz

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Which statement best describes how a mixed meal is prepared in the mouth and stomach before it reaches the duodenum?

Terminal ileum activates trypsinogen with enteropeptidase before any gastric acid has denatured dietary protein Mouth initiates triglyceride emulsification with bile salts while the stomach activates pancreatic proenzymes before chyme enters the duodenum Proximal colon secretes pancreatic lipase, which emulsifies fat before bile reaches the small intestine Mouth reduces particle size and starts starch digestion with salivary amylase; stomach denatures protein and begins digesting it with pepsin into large peptides Stomach completes protein digestion to free amino acids ready for absorption, while saliva packages long-chain fat into chylomicrons

A Terminal ileum activates trypsinogen with enteropeptidase before any gastric acid has denatured dietary protein
B Mouth initiates triglyceride emulsification with bile salts while the stomach activates pancreatic proenzymes before chyme enters the duodenum
C Proximal colon secretes pancreatic lipase, which emulsifies fat before bile reaches the small intestine
D Mouth reduces particle size and starts starch digestion with salivary amylase; stomach denatures protein and begins digesting it with pepsin into large peptides ✓
E Stomach completes protein digestion to free amino acids ready for absorption, while saliva packages long-chain fat into chylomicrons

The answer is D: Mouth reduces particle size and starts starch digestion with salivary amylase; stomach denatures protein and begins digesting it with pepsin into large peptides

Explanation

Why D is correct

See Mouth and Stomach Preparation. Option D is correct: the mouth and stomach each do a small, specific first job before the meal reaches the duodenum (the first part of the small intestine). In the mouth, chewing breaks food into smaller pieces and mixes it with saliva, which gives enzymes more surface to work on, and salivary amylase (an enzyme made by the salivary glands) starts splitting starch into shorter sugar chains. In the stomach, acid denatures protein, meaning it unfolds the protein's tightly folded shape so that its bonds are exposed, and the enzyme pepsin then cuts the protein into large peptides (short chains of amino acids) rather than into free amino acids. Fat digestion mostly has to wait for the small intestine, where bile and pancreatic enzymes join the meal. Memory aid: amylase for starch in the mouth, pepsin for protein in the stomach, and fat later in the duodenum.

Mouth: chewing reduces particle size and salivary amylase starts splitting starch.
Stomach: acid denatures protein and pepsin cuts it into large peptides.
Fat: its digestion mostly waits for the small intestine.

Why the other options are incorrect

A. Terminal ileum activates trypsinogen with enteropeptidase before any gastric acid has denatured dietary protein: Enteropeptidase sits on the brush border of the duodenum and activates trypsinogen after gastric contents arrive. The terminal ileum is not the activation site, and it lies far downstream of the stomach.
B. Mouth initiates triglyceride emulsification with bile salts while the stomach activates pancreatic proenzymes before chyme enters the duodenum: Bile salts enter at the duodenum, not the mouth. Pancreatic protease precursors are activated in the small intestine, not by normal gastric digestion.
C. Proximal colon secretes pancreatic lipase, which emulsifies fat before bile reaches the small intestine: Pancreatic lipase is secreted into the duodenum by the pancreas, not by the colon. Bile salts, not lipase, emulsify fat, and this happens in the small intestine.
E. Stomach completes protein digestion to free amino acids ready for absorption, while saliva packages long-chain fat into chylomicrons: Pepsin only begins protein digestion, producing peptides, and digestion continues in the small intestine. Chylomicrons are assembled inside intestinal lining cells, not in saliva.

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1
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2
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