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Delivery of nutrients to cells

Delivery of nutrients to cells. Chapter 22. Preparation for absorption. Digestive enzymes act as food is moved along alimentary canal Small intestine has a structure suited to absorption - large surface area - villi & microvilli - Very thin lining

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Delivery of nutrients to cells

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  1. Delivery of nutrients to cells Chapter 22

  2. Preparation for absorption • Digestive enzymes act as food is moved along alimentary canal • Small intestine has a structure suited to absorption • - large surface area • - villi & microvilli • - Very thin lining • - Dense network of vessels (capillaries & lacteals)

  3. Nutrient absorption • Glucose & amino acids into capillaries via epithelium • - direct to bloodstream • Lipids into lacteals • - lymphatic system • Other nutrients (calcium, iron, vitamins) absorbed into capillaries • Bile salts act as an emulsifier of lipids • -ve heads repel each other • - made in liver, stored in gall bladder • - with lipase, speeds up lipid digestion

  4. Lipid absorption • Lipase: • Products + Bile Salts = Micelles • Micelles move to epithelium surface • Monoglyceride + Fatty acids diffuse through into epithelial cells • Once through Smooth ER built back into triglycerides • Coated with lipoprotein and exit by exocytosis • Enter lacteals – lymphatic systems

  5. Liver Blood Supply • Hepatic artery in (oxygenated) • Hepatic vein away (deoxygenated) • Hepatic portal vein (deoxygenated from the gut) • – part of the portal system • - allows liver to process digestion products • Liver regulates nutrient & urea concentrations • Hepatic artery – normal conc of nutrients & urea • Hepatic portal vein – normal urea, high conc of digestion products • Hepatic vein – normal nutrient conc., high conc of urea

  6. Role of liver in metabolism • Glucose: • In excess – insulin converts glucose to glycogen • Further excess converted into fat • Low levels – glucagon converts glycogen to glucose • Lipids: • Dietary lipids removed from circulation • - make cholesterol (hormones), lipoproteins etc • Protein: • Make plasma proteins – albumins, globulins, fibrinogen • Amino acid conversions – transaminase enzymes • - amino acids converted

  7. Fate of absorbed materials • Carbohydrate: • Absorbed by cells for energy • Stored as glycogen or fat • Lipids: • Circulated in lipoproteins • Glycerol & Fatty acids absorbed by cells for energy • Excess FA’s & Glycerol stored in adipose tissue • Proteins: • Absorbed by cells for protein synthesis • Energy source to cells (following deamination) • Vitamins & Minerals: • Metal ions e.g iron – enzyme activators (co-factors) • Vitamins (organic, non-proteins) – co-enzymes

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