Gastrointestinal Secretion, Digestion and Absorption Quiz

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.

E is wrong because pepsin is produced by gastric chief cells, not by salivary glands, and the stomach does not emulsify fat; emulsification is performed by bile salts after bile enters the duodenum. C is wrong because pancreatic amylase is released by the pancreas into the duodenum, not into the mouth, and the stomach performs only limited early fat digestion; free fatty acids are mainly absorbed in the small intestine, not the stomach. In A, the first clause is true because the mouth does begin some fat digestion with lingual lipase, but the second clause is wrong: pepsin starts protein digestion and gives large peptides; free amino acids are produced mainly by pancreatic and brush-border enzymes in the small intestine. B is tempting because its first half mirrors the correct mouth preparation, but the stomach does not absorb most dietary glucose; glucose absorption occurs mainly in the small intestine once carbohydrate digestion has produced monosaccharides.