The Digestive System

The Digestive System - The Digestive System P A R T A...

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Unformatted text preview: The Digestive System P A R T A Digestive System: Overview The alimentary canal or gastrointestinal (GI) tract digests and absorbs food Alimentary canal mouth, pharynx, esophagus, stomach, small intestine, and large intestine Accessory digestive organs teeth, tongue, gallbladder, salivary glands, liver, and pancreas Figure 23.1 Digestive Process The GI tract is a disassembly line Nutrients become more available to the body in each step There are six essential activities: Ingestion, propulsion, and mechanical digestion Chemical digestion, absorption, and defecation Figure 23.2 Gastrointestinal Tract Activities Ingestion taking food into the digestive tract Propulsion swallowing and peristalsis Peristalsis waves of contraction and relaxation of muscles in the organ walls Mechanical digestion chewing, mixing, and churning food Peristalsis and Segmentation Figure 23.3 Gastrointestinal Tract Activities Chemical digestion catabolic breakdown of food Absorption movement of nutrients from the GI tract to the blood or lymph Defecation elimination of indigestible solid wastes GI Tract External environment for the digestive process Regulation of digestion involves: Mechanical and chemical stimuli stretch receptors, osmolarity, and presence of substrate in the lumen Extrinsic control by CNS centers Intrinsic control by local centers Receptors of the GI Tract Mechano and chemoreceptors respond to: Stretch, osmolarity, and pH Presence of substrate, and end products of digestion They initiate reflexes that: Activate or inhibit digestive glands Mix lumen contents and move them along Nervous Control of the GI Tract Intrinsic controls Nerve plexuses near the GI tract initiate short reflexes Short reflexes are mediated by local enteric plexuses (gut brain) Extrinsic controls Long reflexes arising within or outside the GI tract CNS centers and extrinsic autonomic nerves Nervous Control of the GI Tract Figure 23.4 Peritoneum and Peritoneal Cavity Peritoneum serous membrane of the abdominal cavity Visceral covers external surface of most digestive organs Parietal lines the body wall Peritoneal cavity Lubricates digestive organs Allows them to slide across one another Peritoneum and Peritoneal Cavity Figure 23.5a Peritoneum and Peritoneal Cavity Mesentery double layer of peritoneum that provides: Vascular and nerve supplies to the viscera Hold digestive organs in place and store fat Retroperitoneal organs organs outside the peritoneum Peritoneal organs (intraperitoneal) organs surrounded by peritoneum Peritoneum and Peritoneal Cavity Figure 23.5b Blood Supply: Splanchnic Circulation Arteries and the organs they serve include The hepatic, splenic, and left gastric: spleen, liver, and stomach Inferior and superior mesenteric: small and large intestines Blood Supply: Splanchnic...
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This note was uploaded on 01/06/2012 for the course BIOL 2402 taught by Professor Elainefanin during the Fall '11 term at Collins.

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The Digestive System - The Digestive System P A R T A...

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