Digestion and absorption

• Salivary gland- secretes amylase which catalyses the hydrolysis of starch to maltose
• Oesophagus- carries food from the mouth to the stomach, made up of thick muscular wall
• Stomach- muscular sac that produces enzymes, stores and digests food, produces mucus
• Pancreas- produces protease, lipases and amylase
• Carbohydrate digestion

  • food is mixed with amylase from salivary glands
  • catalyses hydrolysis of glycosidic bonds in starch and produces maltose
  • food is swallowed and enters acidic stomach, denatures amylase preventing further breakdown
  • food passed along small intestine and mixed with pancreatic juices
  • continues to hydrolyse starch to maltose
  • smooth muscle in ileum wall push food along ileum
  • molecule absorbed into epithelial cells
• protein digestion and absorption

  • endopeptidase- hydrolyses peptide bonds between amino acid in the centre of a protein molecule forming a series of peptide molecules
  • exopeptidase- hydrolyses peptide bonds on the terminal amino acid of the peptide molecule formed by endopeptidases
• Lipid absorption

  1. Bile salts are produced in the liver act on lipids to split them up into tiny droplets called micelles- called emulsification and increases the surface area of the lipids
  2. ester bonds joining the three fatty acids and glycerol molecule are then hydrolysed. Products of the reaction are packaged into micelles
  3. movement of material in the intestinal lumen means micelles come into contact with the epithelial cells that make up the villi
• Lipid absorption

  4. the micelles break down realising monoglycerides and fatty acids

  5. monoglycerides and fatty acids are non-polar molecules so can diffuse across the cell-surface membrane and into the epithelial cells

  6. fatty acids and monoglycerides are transported to the endoplasmic reticulum where they are recombined to form triglycerides

  7.Triglycerides then move from the endoplasmic reticulum to the Golgi apparatus where they associate with cholesterol and lipoproteins to form structures called chylomicrons
• Lipid absorption

  8. Chylomicrons move out the epithelial cell by exocytosis and enter the lacteals

  9. pass from lacteals into the blood stream

  10. triglycerides in the chylomicrons are hydrolysis by an enzyme in the endothelial cells that make up the capillaries. The fatty acids then diffuse into the cells that make up tissues where they are used for various metabolic processess