The Digestive Syste7

The Digestive Syste7 - o Pepsin starts protein digestion o...

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The Digestive System Movements and Secretions in the Digestive System The digestive system is regulated by neural and hormonal mechanisms. Intramural plexuses are responsible for local reflexes. Oral Cavity, Pharynx, and Esophagus Amylase in saliva starts starch digestion. Mucin provides lubrication. Mastication is accomplished by the teeth, which cut, tear, and crush the food. During the voluntary phase of deglutition, a bolus of food is moved by the tongue from the oral cavity to the pharynx. During the pharyngeal phase of deglutition, the soft palate closes the nasopharynx, and the epiglottis closes the opening into the larynx. Pharyngeal muscles move the bolus to the esophagus. During the esophageal phase of deglutition, a wave of constriction (peristalsis) moves the food down the esophagus to the stomach. Stomach Secretions of the stomach. o Mucus protects the stomach lining. o Hydrochloric acid kills microorganisms and activates pepsin.
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Unformatted text preview: o Pepsin starts protein digestion. o Intrinsic factor aids in vitamin B 12 absorption. o Gastrin helps regulate stomach secretions and movements. • Regulation of stomach secretions. o During the cephalic phase, the stomach secretions are initiated by the sight, smell, taste, or thought of food. Gastrin stimulates stomach secretions. o During the gastric phase, partially digested proteins or distention of the stomach also promotes secretion. o During the intestinal phase, acidic chyme in the duodenum stimulates neuronal reflexes and the secretion of hormones that induce and then inhibit gastric secretions. Gastrin stimulates stomach secretion. Secretin, gastric inhibitory polypeptide, and cholecystokinin inhibit gastric secretion. • Movement in the stomach. o Mixing waves mix the stomach contents with the stomach secretions to form chyme. o Peristaltic waves move the chyme into the duodenum....
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