Digestion in the stomach
The stomach is a somewhat wide, bag-like organ. Waves of peristalsis in its muscular wall churn the food, breaking it into small pieces and mixing it into a paste called chyme.
Gastric juice
The secretions poured into the stomach together make gastric juice. Its main contents are hydrochloric acid and pepsin. The acid makes pepsin active; pepsin begins the digestion of protein, producing polypeptides.
Protein
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Polypeptides
- In infants, gastric juice also contains rennin, which curdles milk.
- Food stays in the stomach for about three hours. No products of digestion are absorbed there, but water, glucose and some medicines are.
- The chyme — part-digested protein, carbohydrate, undigested lipid, water, salts and vitamins — moves on into the duodenum, the first part of the small intestine.
Why you feel hungry
The stomach keeps contracting even when empty, and the longer it stays empty the faster the contractions — sometimes painfully. That is the feeling of hunger: a signal that the body needs food.