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Human Systems

Human Systems. 8.4 Digestion. Digestion. Initial digestion of carbohydrates: mouth Initial digestion of proteins: stomach Complete digestion of carbs and proteins: small intestine Initial and complete digestion of lipids: small intestine

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Human Systems

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  1. Human Systems 8.4 Digestion

  2. Digestion • Initial digestion of carbohydrates: mouth • Initial digestion of proteins: stomach • Complete digestion of carbs and proteins: small intestine • Initial and complete digestion of lipids: small intestine • Small intestine- approx. 7 m in length, 2.5 cm in diameter (humans)- in mammals, length related to diet • Absorption of all macronutrients into the bloodstream occurs in the small intestine

  3. Small Intestine • 3 sections: duodenum, jejunum, ileum • Majority of digestion in duodenum (first 25 – 30 cm) • Contents enter from stomach – move by peristalsis • Specific structures for absorption:- villi: finger-like projections to increase surface area- microvilli: fine, thread-like extensions on each villus (further increase surface area)- capillary network: on each villus (transport monosaccharidesand amino acids) - lacteals: intertwines with lymph vessels to transport materials (fats) Villi

  4. Pancreas • Contents enter small intestine coated in HCl & pepsin- initiates conversion of prosecretin into secretin • Carried to pancreas • Signals release of bicarbonate ions (HCO3-) - carried to small intestine • Buffer HCl in gastric fluid- raise pH to ~ 9.0 • Inactivates pepsin • Protects lining of small intestine

  5. Pancreas • Pancreatic secretions also include trypsinogen, erepsins, amylase, lipase • Trypsinogen (inactive): converted to trypsin (active) by enterokinase in small intestine- trypsin breaks down polypeptides into peptides • Erepsins: from pancreas and small intestine- complete protein digestion into individual amino acids • Amylase: continue carbohydrate digestion- broken down into disaccharides • small intestine releases disaccharidases- completes digestion of carbs • Lipase: break down fats into glycerol and fatty acids

  6. Protein digestion in small intestine. Made possible by release of pancreatic juices

  7. Liver and Gall Bladder • Liver produces bile- bile salts to help fat digestion • Bile stored in gall bladder • Fats detected in small intestine:- hormone cholecystokinin (CCK) released- carried to gall bladder- bile salts released • Act to emulsify fat globules (physical digestion)- prepares fat for chemical digestion by lipases CCK and lipids

  8. Liver and Gall Bladder • Bile contains pigments- liver breaks down hemoglobin- brown colour of feces • Liver stores glycogen and vitamins • Able to detoxify substances- harmful ones soluble, dissolve in blood, excrete in urineex) alcohol • See table 2 pg 267 • Problems: gall stones, cirrhosis

  9. Large Intestine • Chemical digestion complete • Colon: largest part of large intestine- stores wastes, allows for water and mineral reabsorption • E. coli bacteria found here- use wastes to produce vitamin B and K • Cellulose: undigested- provides bulk • Build up: receptors signal bowel movement • Not enough cellulose = fewer bowel movements Colonoscopy Round Worm

  10. Control of Digestion • Nervous system- sight/taste/smell signal production gastric juices- swallowing motions • Hormonal systemEx) secretin (release HCO3-), gastrin (release HCl) • Speed of digestion- controlled by receptors- large meal: more receptors activated • Meal very fatty: release of enterogastrone- slows peristalsis

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