Food passes through the stomach within 2 hours, little as 30 min Little feed digestion of proteins and fats Bolus is converted to liquid called Chyme Epithelial cells extend down into the lamina propria where they form columns of secretory cells called Gastric Glands. Gastric glands contain 3 types of Exocrine Gland Cells secreting their products into the stomach lumen: 1) Goblet Cells - secrete mucus
2) Parietal Cells – produce Hydrochloric acid (HCl), up to 72L/24 hrs.
Strongly acidic fluid of the stomach kills many microbes in food. HCl partially denatures proteins in food stimulates the secretion of hormones that promote the flow of bile and pancreatic juice. 3) Chief Cells - secrete Pepsinogen (pepsin) to break down proteins and Gastric Lipase to break down fats. All the above secretions form Gastric Juice . Gastric glands also include a type of Enteroendocrine Cell – G Cell which secretes the hormone Gastrin into the bloodstream.
Digestion in the Stomach
Mixing Waves : beginning several minutes after food enters the stomach, gentle, rippling, peristaltic movements pass over the stomach every 15 – 25 seconds. These waves macerate food, mix it with secretions from gastric glands, and reduce it to a chyme. As food reaches the pylorus, each mixing wave forces some chyme into the duodenum through the Pyloric Sphincter called Gastric Emptying. Only small amounts of food are digested (chemically) in the stomach. However, mucus cells of the stomach absorb some water, ions, short-chain fatty acids, and certain drugs such as aspirin and alcohol.
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