The first three glands listed in the preceding list are exocrine glands

The first three glands listed in the preceding list are exocrine glands

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The first three glands listed in the preceding list are exocrine glands, whose secretions, collectively  called gastric juice, enter the stomach and mix with food. The last gland is an endocrine gland,  whose hormone secretions enter the blood supply. The stomach serves a variety of functions:  Storage.  Because of its accordionlike folds (called rugae), the wall of the stomach can  expand to store two to four liters of material. Temporary storage is important because you eat  considerably faster than you can digest food and absorb its nutrients.  Mixing.  The stomach mixes the food with water and gastric juice to produce a creamy  medium called  chyme.   Physical breakdown.  Three layers of smooth muscles (rather than the usual two) in the  muscularis externa churn the contents of the stomach, physically breaking food down into  smaller particles. In addition, HCl denatures (or unfolds) proteins and loosens the cementing 
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Unformatted text preview: substances between cells (of the food). The HCl also kills most bacteria that may accompany the food. Chemical breakdown. Proteins are chemically broken down by the enzyme pepsin. Chief cells, as well as other stomach cells, are protected from self-digestion because chief cells produce and secrete an inactive form of pepsin, pepsinogen. Pepsinogen is converted to pepsin by the HCl produced by the parietal cells. Only after pepsinogen is secreted into the stomach cavity can protein digestion begin. Once protein digestion begins, the stomach is protected by the layer of mucus secreted by the mucous cells. Controlled release. Movement of chyme into the small intestine is regulated by a sphincter at the end of the stomach, the pyloric sphincter....
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This note was uploaded on 11/10/2011 for the course PT 101 taught by Professor Staff during the Spring '10 term at Texas State.

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