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A Tour of the Digestive System

A Tour of the Digestive System. Where is the food now? The duodenum. How broken down is it? Physical digestion: Teeth and stomach churning broke it into pieces Bile broke the fats into smaller globs Chemical digestion: Salivary amylase: starch  maltose

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A Tour of the Digestive System

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  1. A Tour of the Digestive System

  2. Where is the food now? • The duodenum

  3. How broken down is it? • Physical digestion: • Teeth and stomach churning broke it into pieces • Bile broke the fats into smaller globs • Chemical digestion: • Salivary amylase: starch  maltose • Pepsin in stomach: protein  peptides • Pancreatic amylase: starch  maltose • Trypsin from the pancreas: protein  peptides • Lipase from the pancreas: fats  glycerol + fatty acids

  4. What still needs to be broken down? • FATS? fats  glycerol + fatty acids • PROTEINS? protein  peptides want AMINO ACIDS • CARBOHYDRATES? starch  maltose want GLUCOSE • NUCLEIC ACIDS? DNA / RNA  nucleotides  P + sugar + base

  5. Maltase Peptidase Digestive Enzymes from the Interstitial glands Glucose Maltose Amino Acids Peptide

  6. Cells in Small Intestine make enzymes • Interstitial glands… • Peptidases break down proteins • Amino acids • Maltase breaks down maltose • Glucose • Other disaccharides are also broken down, e.g. lactase breaks down lactose • Nucleosidases breaks down nucleotides • P, sugar, N base

  7. Inside the small intestine • Increased surface area: • Large folds • Villi stick out from the folds • Microvilli stick out from the villi ~600m2 (size of a baseball diamond)

  8. Outer wall Pathway for Food Inner wall The Villi

  9. Villi • Layer of cells around villi (epithelium) • Lacteal in the centre • lymphatic vessel • Blood capillaries surround the lacteal

  10. Absorbing nutrients • Fats enter the lacteal • Absorbed by lymphatic system Lipase Glycerol Fatty Acid Fatty Acid Fatty Acid

  11. Absorbing nutrients • sugars and amino acids enter the blood • Capillaries join hepatic portal vein to the liver How long is “food” here? Up to 4 hours

  12. A close up look at villi

  13. A Tour of the Digestive System

  14. Large Intestine • Colon • ~1.5m long • 3 parts: • ascending • transverse • descending • Rectum • Last 20 cm • Anus • Sphincter at the end

  15. Caecum • pouch at the start of the large intestine • Appendix • a vestigial organ • (no current function)

  16. What does the large intestine do? • Reabsorption of water • Absorption of some vitamins • Also contains: • bile pigments • heavy metals • billions of E. coli bacteria • break down some indigestible food • produce some vitamins, amino acids, and other growth factors

  17. Indigestion? Disorders in the large intestine and symptoms http://www.youtube.com/watch?v=1ZIK6Ua20JA&feature=channel_page http://www.youtube.com/watch?v=0yLPtYH6xfE Overall review of digestion: http://www.youtube.com/watch?v=QtDgQjOGPJM

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