Wednesday, January 30, 2008

The stomach

If you were to lay your digestive tract out on a table, most of it would look like a simple, rather narrow tube. The exception is your stomach, a pouchy part just below your gullet (esophagus).
Like most of the digestive tube, your stomach is circled with strong muscles whose rhythmic contractions — called peristalsis — move food smartly along and turn your stomach into a sort of food processor that mechanically breaks pieces of food into ever smaller particles. While this is going on, glands in the stomach wall are secreting stomach juices — a potent blend of enzymes, hydrochloric acid, and mucus.
One stomach enzyme — gastric alcohol dehydrogenase — digests small amounts of alcohol, an unusual nutrient that can be absorbed directly into your bloodstream even before it’s been digested. Other enzymes, plus stomach juices, begin the digestion of proteins and fats, separating them into their basic components — amino acids and fatty acids. For the most part, digestion of carbohydrates comes to a screeching — though temporary — halt in the stomach because the stomach juices are so acidic that they deactivate amylases, the enzymes that break complex carbohydrates apart into simple sugars. However, stomach acid can break some carbohydrate bonds, so a bit of carb digestion does take place. Back to the action. Eventually, your churning stomach blends its contents into a thick soupy mass called chyme (from cheymos, the Greek word for juice). When a small amount of chyme spills past the stomach into the small intestine, the digestion of carbohydrates resumes in earnest, and your body begins to extract nutrients from food.

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