chapter21c The Digestive System 3

chapter21c The Digestive System 3 - Chapter 21c The...

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Unformatted text preview: Chapter 21c The Digestive System The Cephalic Phase Chemical and mechanical digestion begins in the mouth Salivary secretion is under autonomic control Softens and lubricates food Chemical digestion: Salivary amylase and some lipase Saliva also has a protective function Chewing: mastication Swallowing Reflex Figure 21-24, step 1 Tongue pushes bolus against soft palate and back of mouth, triggering swallowing reflex. Hard palate Tongue Bolus Epiglottis Tonically contracted upper esophageal sphincter Larynx Soft palate Glottis 1 Swallowing Reflex Figure 21-24, step 2 Upper esophageal sphincter relaxes while epiglottis closes to keep swallowed material out of the airways. Epiglottis 2 Swallowing Reflex Figure 21-24, step 3 Food moves downward into the esophagus, propelled by peristaltic waves and aided by gravity. 3 The Gastric Phase Storage Stomach Digestion Stomach Acid, enzymes, and signal molecules Protection The Gastric Phase Activity of secretory cells of the gastric mucosa Figure 21-25 Gastric mucosa Opening of gastric gland Cell Types Substance Secreted Stimulus for Release Function of Secretion Mucous neck cell Mucus Bicarbonate Tonic secretion; with irritation of mucosa Secreted with mucus Physical barrier between lumen and epithelium Buffers gastric acid to prevent damage to epithelium Parietal cells Gastric acid (HCl) Intrinsic factor Acetylcholine, gastrin, histamine Activates pepsin; kills bacteria Complexes with vitamin B12 to permit absorption Enterochromaffin- like cell Histamine Acetylcholine, gastrin Stimulates gastric acid secretion Chief cells Pepsin(ogen) Gastric lipase Acetylcholine; acid, secretin Digests proteins Digests fats D cells Somatostatin Acid in the stomach Inhibits gastric acid secretion G cells Gastrin Acetylcholine, peptides and amino acids Stimulates gastric acid secretion The Gastric Phase Integration of cephalic and gastric phase secretion in the stomach Figure 21-26 Lumen of...
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chapter21c The Digestive System 3 - Chapter 21c The...

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