Intro to Nutrition #53: THE DIGESTIVE SYSTEM Anatomy: What Happens in the Stomach During Digestion?

Intro to Nutrition #53: THE DIGESTIVE SYSTEM Anatomy: What Happens in the Stomach During Digestion?


Besides serving as a holding area for ingested
food, the stomach continues the demolition job begun by the mouth by further degrading
food both physically and chemically. Protein digestion begins in the stomach and is the
main type of enzymatic breakdown that occurs there. HCl produced by stomach glands denatures
dietary proteins in preparation for enzymatic digestion. The most important protein-digesting
enzyme produced by the gastric mucosa is pepsin. In infants, however, the stomach glands also
secrete rennin, an enzyme that acts on the milk protein casein, converting it to a curdy
substance that looks like soured milk. Additionally, lingual lipase released by the minor salivary
glands may digest some triglycerides in the stomach for a short time before the lipase
itself is digested. Two common lipid-soluble substances, alcohol and aspirin, pass easily
through the stomach mucosa into the blood. Both alcohol and aspirin may cause gastric
bleeding, so these substances should be avoided by people with gastric ulcers. Despite the
obvious benefits of preparing food to enter the intestine, the only stomach function essential
to life is secretion of intrinsic factor. Intrinsic factor is required for intestinal
absorption of vitamin B12, needed to produce mature erythrocytes. In its absence, pernicious
anemia results. However, if vitamin B12 is administered by injection, individuals can
survive with minimal digestive problems even after a total gastrectomy, or stomach removal.
And finally, chyme is delivered into the small intestine, where the next stage of the digestive
process occurs.

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