Regulating Digestion In The Stomach

Digestion in the stomach can be stimulated in a variety of ways. The thought, sight, or smell of food can stimulate the stomach to secrete digestive fluids. When food enters the

Food Entering The Stomach
Figure 6.2 Gastric pits, found in the lining of the stomach, contain special cells that secrete chemicals used in digestion. Shown here is a micrograph of gastric pits.

stomach, it stretches the walls of the stomach, resulting in pressure on specialized nerves within the smooth muscle layers of the stomach. These nerves relay a signal that stimulates gastrin secretion. In addition to the action of the stretch receptors, certain chemicals, such as caffeine and alcohol, cause stomach fluids to be produced. Highly alkaline food also causes stomach secretions to flow.

Increasing amounts of hydrochloric acid in the stomach causes the parietal cells to decrease secretion of the acid, slowing production of pepsin and slowing down the initial breakdown of proteins. Stomach digestion is also slowed down by the actions of the small intestine. When the acidic stomach contents (called chyme) enter the small intestine, the nervous system stimulation of the G cells is inhibited. The presence in the small intestine of protein fragments called peptides and fatty acids from triglyceride breakdown also inhibits the nervous system stimulation of the G cells and slows down the mixing of the stomach contents. The interplay of the stomach and small intestine ensures that the small intestine receives chyme in amounts that it can handle. In addition to continuing digestion in the intestine, this control process includes the neutralization of stomach acids. The small intestine does not have the relatively thick, protective layer of mucus found in the stomach. The hydrochloric acid would harm the intestinal lining and cause a type of ulcer (see the "Your Health" section concerning ulcers on page 55).

Few materials are absorbed through the stomach lining. The stomach functions to prepare food for further digestion and absorption in the small intestine. Glucose, caffeine, and alcohol are three chemicals that are absorbed through the stomach lining. Water will only be absorbed in the stomach if a sufficient amount of glucose is dissolved in the water. The formulation of sports drinks for athletes takes advantage of this dual absorption to rapidly increase the

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  • robert
    Does thought,sight and smell of food stimulate the digestive process?
    7 years ago

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