Digestion and absorbtion

• Explain what happens in digestion

  large insoluble molecules are hydrolysed into smaller soluble molecules that can be absorbed across cell membranes into the blood
• Describe the digestion of starch

  Amylase hydrolyes starch into maltose

  Membrane bound Maltase hydrolyes maltose to glucose

  Hydrolysis of glycosidic bong
• Describe the digestion of disaccarides

  maltase hydrolyses maltose into 2x glucose

  lactase hydrolyes lactose into galactose and glucose

  sucrase hydrolyses sucrose into fructose and glucose

  hydrolysis of glycosidic bond
• Describe the digestion of lipids including bile salts

  Bile salts emulsify lipids causing them to form smaller lipid droplets

  this increases surface area pf lipids for faster lipase activity

  Lipase hydrolyses lipids into monoglycerides and fatty acids

  hydrolysis of ester bond
• describe the digestion of proteins

  Endopeptidases-hydrolyses internal peptide bonds within the polypeptide into smaller peptides

  Exopeptidases-hydrolyses peptide bonds at the end of the polypeptide chain into single amino acids

  membrane bound dipeptidases-hydrolyses peptide bond in a dipeptide into to 2 amino acides

  hydrolysis of peptide bond
• suggest why membrane bound enzymes are important in digestion

  membrane bound enzymes are located on the cell membranes of epitheleal cellls lining ileum by hydrolysing molecules at the site of absorbtion they maintain the concentration gradient for absorbtion
• describe the pathway for absorbtion of products of digestions in mammals

  lumen inside of ileum-cells lining ileum-blood
• describe the absorption of amino acids and monosaccarides

  1. sodium ions are actively transported from epithelial cells lining ileum to blood by K+/NA+ pump establishing a concentration gradient of Na+
  2. Na+ enters epithelial cell down its concentration gradient with glucose against its concentration gradient via a co transporter protein
  3. Glucose moves down a concentration gradient into blood via facilitated diffusion
• Micelles


  • Contain bile salts, monoglycerides and fatty acids
  • Make monoglycerides and fatty acids more soluble in water
  • Carry/release fatty acids and monoglycerides to cells lining of ileum
  • Maintain high concentration of fatty acids to cells
• Absorption of lipids


  1. Monoglycerides/fatty acids absorbed into epithelial cells by diffusion

  2. Triglycerides reformed in epithelial cells and aggregate into globules

  3. Globules coated with proteins forming chylomicrons which are then packaged into vesicles

  4. Vesicles move to cell membrane and leave via exocytosis

  5. Enters lymphatic vessels and eventually return to blood circulation