Digestion and Absorption

• Large molecules are hydrolysed into smaller molecules
• Digestion of Carbohydrates:

  • Begins in mouth, then duodenum, then completed in the ileum
  • Involves amylase and membrane-bound disaccharidases
  • Amylases produced in the salivary glands and pancreas, hydrolysing polypeptides into maltose, breaking glycosidic bonds
  • Sucrase and Lactase are membrane-bound enzymes
• DIgestion of Proteins:

  • Begins in the stomach, then duodenum, then ends in ileum
  • Endopeptidases hydrolyse peptide bonds in the middle
  • Exopeptidases hydrolyse peptide bonds at the ends
  • Membrane Bound Peptidases hydrolyse peptide bonds between 2 amino acids
• Digestion of Lipids:

  • Digested by lipase and bile salts
  • Lipase is produced in the pancreas, hydrolysing ester bonds in triglycerides to form monoglycerides and fatty acids
  • Bile salts produced in the liver emulsify lipids into micelles to increase surface area for lipase to act on
  • Micelles include fatty acids, glycerol, monoglycerides and bile salts
  • Micelles are non-polar and can simply diffuse across membranes
  • Micelles are modified back into triglycerides in the golgi and ER once in the cell
• Absorption occurs in the ileum, walls are covered in villi and microvilli to increase surface area, with a network of capillaries to reduce diffusion distance
• Glucose and Amino Acids require active transport and co-transport to be absorbed as there is a higher concentration in the epithelial cell