lectures_14-15

lectures_14-15 - About this Chapter Digestion function and...

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About this Chapter Digestion function and processes Anatomy of the digestive system Motility Secretion Regulation of GI function Digestion and absorption
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DIGESTION Function and processes of the digestive system Gastrointestinal (GI) tract: - move materials - digestion of food Challenges to GI tract: - protect from autodigestion - ulcers - dehydration - diarrhea
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DIGESTION Function and processes of the digestive system absorbed nutrients enter cells - cellular metabolism - used for energy or stored - hormones play a role in gut function as well as cellular metabolism
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DIGESTION Function and processes of the digestive system repel foreign invaders: - largest contact area - several defense mechnisms - mucus, enzymes, acid, lymphoid tissue (GALT) - 80% of immunoglobulin-producing cells - small intestine
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Anatomy of the digestive system small intestine: - mostly absorption and digestion - divided into three sections 1. Duodenum 2. Jejunum 3. Ileum large intestine: - colon and rectum - watery chyme converted to semisolid feces - distention of rectal wall - triggers defecation reflex
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Modifications to increase lumen surface area - rugae in the stomach - plicae in the intestine
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GI tract wall has four layers: basic structure of the GI wall is similar the four layers are: 1. Mucosa 2. Submucosa 3. Smooth muscle 4. Connective tissue - serosa
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Figure 21-2c: ANATOMY SUMMARY: The Digestive System The mucosa: epithelial cells - single layer Lamina propria Muscularis mucosae
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Epithelial cells - most variable feature of the GI tract Stomach has four major types: 1. Mucus cells - mucus 2. Parietal cells - HCl 3. Chief cells - pepsin 4. G cells - gastrin
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Dominant cells in the intestine: 1. Absorptive cells - move nutrients to ECF 2. Endocrine cells 3. Goblet cells - mucus 4. Other secretory cells - mast cells - histamine Average life span of cells - a few days
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Cell to cell junctions vary: - stomach: tight junctions - intestine: leaky
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The mucosa: epithelial cells - single layer lamina propria: - subepithelial connective tissue - contains nerve fibers - contains blood and lymphatic vessels - wandering immune cells - macrophages and lymphocytes - Peyer’s patches - collection of lymphoid tissue
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The mucosa: epithelial cells - single layer lamina propria muscularis mucosa: - separates mucosa from submucosa - contraction of this smooth muscle - alter effective surface area
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DIGESTION Function and processes of the digestive system four basic processes of the digestive system: 1. Motility 2. Secretion 3. Digestion 4. Absorption
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Motility: moving food from mouth to anus mechanical mixing: - maximizes exposure to digestive enzymes and absorptive epithelium smooth muscle - contracts spontaneously single unit smooth muscle connected by gap junctions
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Motility Tonic contractions Sustained Occur in smooth muscle sphincters and stomach Keep bolus from moving backwards Phasic contractions Last a few seconds Peristalsis moves bolus forward Segmentation mixes
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Figure 21-5a
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lectures_14-15 - About this Chapter Digestion function and...

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