Digestion and Absorption

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Information about Digestion and Absorption

Published on February 24, 2014

Author: drmustansar

Source: authorstream.com

Digestion and Absorption: Digestion and Absorption Digestive System : Digestive System Reduces particle size Helps to absorb micronutrients and trace elements Sets a physical and immunologic barrier Digestion: Digestion Breaks down Carbohydrates (starch and sugar) → single sugar molecules Proteins → amino acids Fats → fatty acids, glycerol Enzymes: Enzymes Proteins that break bonds The Digestive System: The Digestive System Is a long tube from the mouth to the anus Digestive System: Digestive System Mouth to anus Epithelium lines the lumen Barrier to invaders Submucosal layer Muscularis Taste and smell Peristalsis: Peristalsis Muscular contractions that move food along throughout GI tract The Mouth: The Mouth Mastication: chewing Saliva Salivary glands produce about 1.5 liters of saliva daily Salivary amylase (ptyalin) begins to break down starch (inactivated in the stomach) PowerPoint Presentation: Salivary lipase: begins fat digestion, but has minimal effect Mucus to lubricate the food for easier swallowing Lysozyme to kill bacteria PowerPoint Presentation: Taste receptors: sweet, sour, salty, bitter, savory Enzymes to help break down fatty acids Tongue Swallowing: Swallowing Bolus is the food swallowed at one time Epiglottis blocks windpipe, prevents choking The Esophagus: The Esophagus Long tube Connects pharynx to the stomach Peristalsis, muscle contraction Lower esophageal sphincter Heartburn The Stomach: The Stomach Lower esophageal sphincter and pyloric sphincter control entry and exit from stomach Storage capacity of ~4 cups Secretion of hydrochloric acid, enzymes, including a protease, gastric lipase; mucus, the hormone gastrin, and intrinsic factor (B12) Stomach secretes about 2000-2500 ml of gastric juice daily Stomach: Stomach pH of stomach is low, 1 to 4; kills many bacteria and micro-organisms Achlorhydria, gastrectomy, GI dysfunction or disease ↑ risk of bacterial overgrowth in the intestines PowerPoint Presentation: Protein digestion begins with pepsinogen which is converted to active pepsin in acidic stomach environment Chief cells secrete acid-stable gastric lipase, which has minor effect on shorter-chain triglycerides Stomach: Stomach Most of a liquid meal exits in 1 to 2 hours and most of a solid meal in 2 to 3 hours Formation of chyme Mucus layer protects stomach from digestion Very little absorption of nutrients Physiology of the Stomach : Physiology of the Stomach Stomach Acid: Stomach Acid Activates digestive enzymes Partially digests dietary protein Assists in calcium absorption Makes dietary minerals soluble for absorption The Small Intestine: The Small Intestine Most digestion and absorption happens here About 5-7 meters Duodenum (.5 meters) Jejunum (2-3 meters) Ileum (3-4 meters) The Small Intestine: The Small Intestine Folded walls with villi projections Absorptive cells are located on the villi Increases intestinal surface area 600x Rapid cell turnover The Small Intestine: The Small Intestine Nutrient Absorption: Nutrient Absorption Passive diffusion: driven by concentration; fats, water, some minerals Active absorption: uses energy; glucose and amino acids Phagocytosis and pinocytosis: absorptive cells engulf compounds, generally larger molecules, as in immune substances in breast milk Nutrient Absorption: Nutrient Absorption Site of Absorption: Site of Absorption Absorption: Absorption Digestion → small particles End products of digestion: Carbohydrates → monosaccharides Proteins → amino acids Fats → glycerol, fatty acids Absorption: Absorption Through small intestine walls Absorbed into Blood – water soluble nutrients Lymph – fat soluble nutrients Blood → liver → general circulation Liver detoxifies and repackages The Large Intestine: The Large Intestine ~3 1/2 feet in length No villi or enzymes present Little digestion occurs Absorption of water, some minerals, vitamins Bacteria break down fiber; produce Vitamin K Formation of feces for elimination Rectum: Rectum Stool remains Stimulates elimination Muscle contraction Anal sphincters Voluntary control Opens for elimination Accessory Organs: Accessory Organs Salivary glands Pancreas Gallbladder Liver Salivary Glands: Salivary Glands Saliva Works in mouth Moistens Salivary amylase Digests starch The Pancreas: The Pancreas Produces glucagon and insulin (endocrine) Manufactures digestive enzymes → small intestine Secretes pancreatic juices Bicarbonate needed to neutralize chyme when it enters small intestine The Liver: The Liver Produces bile (fat digestion) Enterohepatic circulation The Gallbladder: The Gallbladder Stores bile Concentrates it Releases to small intestine when needed PowerPoint Presentation: The Digestive System PowerPoint Presentation: Sites of Secretion, Digestion, and Absorption Digestion in the Stomach: Digestion in the Stomach Different nutrients leave the stomach at different rates: —Carbohydrates first, followed by protein, fat, and fibrous foods Summary of Enzymatic Digestion and Absorption: Summary of Enzymatic Digestion and Absorption Secretion Enzyme Substrate Action Final Product Saliva Ptyalin Starch Hydrolysis to form dextrins Gastric juice Pepsin Protein Hydrolysis of peptide bonds Gastric lipase Fats Hydrolysis into free fatty acids Summary of Enzymatic Digestion and Absorption —cont’d: Summary of Enzymatic Digestion and Absorption —cont’d Secretion Enzyme Substrate Action Final Product Pancreatic exocrine secretion Lipase Fat Hydrolysis to mono-glycerides Fatty acids Cholesterol esterase Cholesterol Hydrolysis to esters of cholesterol and fatty acids Choles-terol alpha-Amylase Starch, dextrins Hydrolysis Dextrin, maltose Summary of Enzymatic Digestion and Absorption —cont’d: Summary of Enzymatic Digestion and Absorption —cont’d Secretion Enzyme Substrate Action Final Product Pancreatic exocrine secretion Trypsin Protein Hydrolysis Polypeptides Chymotrypsin Protein Hydrolysis Polypeptides Carboxy-peptidase Polypep-tides Hydrolysis Amino acids Ribonuclease Ribonu-cleic acids Hydrolysis Mono- nucleotides Elastase Fibrous protein Hydrolysis Amino acids Summary of Enzymatic Digestion and Absorption —cont’d: Summary of Enzymatic Digestion and Absorption —cont’d Secretion Enzyme Substrate Action Final Product Brush border enzymes Carboxy-peptidase; aminopep-tidase; dipeptidase Polypep-tides Hydrolysis Amino acids Entero-kinase Trypsino-gen Activates to trypsin Polypep-tidases and peptides Sucrase Sucrose Hydrolysis Glucose, fructose Enzymatic Digestion and Absorption —cont’d: Enzymatic Digestion and Absorption —cont’d Secretion Enzyme Substrate Action Final Product Brush border enzymes Isomaltase Dextrin Hydrolysis Glucose Maltase Maltose Hydrolysis Glucose Lactase Lactose Hydrolysis Glucose, galactose Nucleotidases Nucleic acid Hydrolysis Nucleotides Nucleosidases and phosphorylase Nucleosidases Hydrolysis Purine and pyrimidine bases Features of Digestion and Absorption: Features of Digestion and Absorption 92% to 97% of the diet is absorbed Small intestine—key role in digestion and absorption Intestines: 7 meters long —Villi and microvilli/brush border PowerPoint Presentation: Villi of the Human Intestine Refeeding after Starvation : Refeeding after Starvation GI tract compromised after starvation Feeding results in cellular proliferation, which restores normal gastrointestinal architecture and function after a few days Lipids: Lipids The major portion of fat digestion takes place in the small intestine as a result of pancreatic lipase PowerPoint Presentation: Summary of Fat Absorption PowerPoint Presentation: Transport Pathways through the Cell Membrane Large Intestine : Large Intestine 5 feet long Bacterial action to produce gases and organic acids Nutrients formed here—vitamin K, thiamin, vitamin B12, riboflavin PowerPoint Presentation: The Gradual Breakdown of Large Starch Molecules PowerPoint Presentation: Process of Digestion of Carbohydrate PowerPoint Presentation: Sites of Secretion and Absorption into Gastrointestinal Tract Neurotransmitters: Neurotransmitters Alpha-aminobutyric acid: relaxes LES Norepinephrine: decreases motility, increases contractions of sphincters, inhibits secretions Acetylcholine: increases motility, relaxes sphincters, stimulates secretions PowerPoint Presentation: Neurotensin: inhibits release of gastric emptying and acid secretion Neuropeptide-Y: stimulates feeding behavior Hormones and GI Function: Gastrin: Hormones and GI Function: Gastrin Released from gastric mucosa and duodenum in presence of peptides and amino acids; stimulates secretion of hydrochloric acid and pepsinogen; increases gastric antral motility, increases LES tone Hormones and GI function: Secretin: Hormones and GI function: Secretin Secretin: from duodenal mucosa in presence of acid in small intestine; stimulates pancreas to secrete water and bicarb; also insulin and pancreatic enzymes Hormones and GI function: Cholecystokinin (CCK): Hormones and GI function: Cholecystokinin (CCK) Released from proximal small bowel in presence of peptices, amino acids, fat, HCL, stimulates pancreas to release pancreatic enzymes Hormones and GI function: Gastric Inhibitory Polypeptide (GIP): Hormones and GI function: Gastric Inhibitory Polypeptide (GIP) Released from small intestine in presence of glucose and fat; inhibits gastrin-stimulated release of gastric acid Hormones and GI Function (Motilin): Hormones and GI Function (Motilin) Released from stomach and small and large intestine in presence of biliary and pancreatic secretions; promotes gastric emptying and increases GI motility Hormones and GI function: Somatostatin: Hormones and GI function: Somatostatin Released from stomach, pancreas, and upper small intestine in presence of acidity and products of protein and fat digestion; inhibits release of gastrin, motilin, and pancreatic secretions; decreases motility of GI tract Digestion and Absorption: Digestion and Absorption It’s important to know the physiology and function of the GI tract in order to understand the implications of pathophysiology

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