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Digestion

Digestion. Most chemical digestion occurs in the small intestine. The length of the intestines is related to the types of food eaten. Plant material is harder to digest than meats Carnivores have short intestines Omnivores have medium length intestines

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Digestion

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  1. Digestion • Most chemical digestion occurs in the small intestine. • The length of the intestines is related to the types of food eaten. • Plant material is harder to digest than meats • Carnivores have short intestines • Omnivores have medium length intestines • Herbivores have a longest lengths of intestines

  2. Small Intestine • Longest section (7 m) • Small Diameter (2.5 cm) • 3 Parts • Duodenum (25 - 30 cm) – most of the digestion occurs here • Jejunum (3 m) – absorption occurs here • Ileum (4 m) – absorption occurs here

  3. Small Intestine • Walls covered with villi • Sphincter at lower end • Ileo-caecal valve • Peristalsis continues • Receives secretions from • walls of small intestine • liver & gall bladder • pancreas

  4. Absorption • Villi & microvilli • Amino Acids & monosaccharides • directly to blood stream • Lacteal – lymph vessels that transport digested fat • fatty acids & glycerol + colloidal fats

  5. Pancreas

  6. Pancreas • Dual Organ • Endocrine • releases insulin into blood stream • Exocrine • releases digestive enzymes into ducts

  7. How the pancreas protects the intestines:

  8. Pancreas • Bicarbonate ions • neutralizes stomach acid • Trypsinogen • Enterokinase activates enzymes • from wall of small intestine • Becomes Trypsin • Long chain peptides ==> short chain peptides

  9. Pancreas • Erepsin – an enzyme than completes protein digestion • short chain peptides ==> amino acids • Lipase - • fats ==> fatty acids & glycerol • Pancreatic Amylase • starch ==> disaccharides • Maltase (maltose ==> glucose) • Sucrase (sucrose==> glucose + fructose) • lactase (Lactose ==> glucose + galactose)

  10. The enzymes that are used to digest proteins into a.a.’s

  11. Liver • Bile – breaks down fat into smaller pieces. This is not a chemical reaction but physical process (like soap) • Emulsifies fats & neutralizes stomach acid • Stored & released from gall bladder • When fats enter the small intestine, the hormone CCK is released into the blood stream. • CCK causes bile to be released

  12. Liver • Many functions, including • Produces bile salts • Detoxifies harmful chemicals (alcohol) • Toxic wastes converted to less toxic wastes • Ammonia ==> Urea

  13. Liver • Glucose converted to glycogen for storage • Glycogen converted to glucose for energy • Storage of some vitamins (A, B12, D)

  14. Large Intestine (colon) • 1.5 m in length • 7 - 8 cm in diameter • Ascending colon • Transverse Colon • Descending Colon • Sigmoid Colon • Rectum • Anus (sphincter under voluntary control)

  15. Large Intestine • Reabsorption of water • Cellulose (fiber) • helps retain some water in feces • Bacteria in residence • E. coli • syntheizes vitamins B & K

  16. Control of digestion • Nervous and hormonal systems control digestion. • When we sense food we start producing digestive enzymes even before we eat. Hormones: • Gastrin made by the stomach causes the release of HCL • Speed is controled by the nervous system as well as the hormone enterogastrone. This slows digestion so that fats can be digested and absorbed.

  17. Digestive System Disorders • Ulcers • Gallstones • Jaundice • Hernia (Hiatal) • Appendicitis • Perotinitis • Hepatitis • Cirrhosis

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