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 - Dense network of vessels (capillaries & lacteals)

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

Lipid absorption Lipase digests fat into 2 products Products + Bile Salts = Micelles Micelles are water soluble particles They move to epithelium surface of intestine wall Monoglyceride + Fatty acids diffuse through into epithelial cells Once through the Smooth ER - built back into triglycerides Coated with lipoprotein and exit by exocytosis Enter lacteals – lymphatic system

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

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

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