Digestion and Absorption

• Amylase (pancreas, salivary glands) hydrolyses glycosidic bonds converting polysaccharides to disaccharides and maltose.
• Membrane-bound disaccharides (sucrase, lactase) break down sucrose and lactose to monosaccharides (duodenum).
• Proteins are broken down by endopeptidases (hydrolyse peptide bonds between amino acids in the middle of the polymer chain), exopeptidases (end of polymer chain) and membrane-bound peptidases (hydrolyse bond between dipeptidases). It starts in the stomach, then duodenum and finally the ileum.
• Lipids are broken down chemically by lipase (pancreas, hydrolyse ester bonds in triglycerides to form monoglycerides and fatty acids) and by physical digestion with bile salts (emulsify lipids to form micelles).
• Lipid digestion


  1 - lipids coated in bile salts to create an emulsion (increase surface area, allows lipase to work faster)

  2 - micelles formed so fatty acids and monoglycerides more soluble in water and then released to the epithelial cells

  3 - fatty acids and monoglycerides absorbed into the epithelial cells by diffusion

  4 - triglycerides formed in the golgi and when combined with a protein a chylomicron is formed

  5 - vesicles move to the membrane for exocytosis

  6 - chylomicrons absorbed into the lacteal and transported away
• Villi and microvilli on the ileum increase surface area, decrease diffusion distance and there is a capillary network close to maintain the concentration gradient.