Digestion and Absorption

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  • Digestion and absorption
    • The contraction of circular and longitudinal muscle layers of the small intenstine mixes the food with enzymes and moves it along the gut
      • peristalsis - waves of muscle contraction
    • the pancreas secretes enzymes into the lumen of the small intenstine
      • glucose and glucagon
      • digestive enzymes
        • pancreatic juice
          • amylase to digest starch
          • lipases to digest triglycerides, phospholipids
          • proteases to digest proteins and peptides
    • enzymes digest most macromolecules in food into monomers in the small intestine
      • starch is digested into maltose by amylase
      • triglycerides are digested to fatty acids and glycerol by lipase
      • phospholipids are digested to fatty acids, glycerol and phosphate by phospholipase
      • proteins and polypeptides are digested to shorter peptides by protease
      • DNA and RNA into nucleotides by Nucleases
      • Maltose into glucose by maltase
      • lactose into glucose and galactose by lactase
      • sucrose into fructose and glucose by sucrase
      • exopeptides digest polypeptides by removing single amino acids to get to a dipeptide
    • Villi increase the surface area of epithelium over which absorption is carried out
    • Villi absorb monomers formed by digestion as well as mineral ions and vitamins
      • glucose, fructose, galactose and other monosaccharides
      • all of the amino acids
      • fatty acids, monoglycerides and glycerol
      • mineral ions
      • vitamins such as ascorbic acid
    • Different methods of membrane transport are required to absorb different nutrients
      • Tryglicerides
        • digested in monoglycerides and fatty acids
          • simple diffusion in the epithelium
            • tryglicerides in order not to flux back
              • fatty acids absorbed by facilitated diffusion
              • tryglicerides and cholesterol to go into the lacteal - lymph or blood capillaries
          • fatty acids absorbed by facilitated diffusion
      • glucose goes into the epithelium with sodium - potassium pumps by active trnasport
        • sodium co transporter ions go down their concentration gradient - facilitated diffusion

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