Duodenum

• What is digested in the duodenum?

  lipids, carbohydrates and proteins
• What is digested in the intracellular membranes of the microvilli cells?

  Carbohydrates and protein
• The pH of the duodenum is 7
• Pancrease secretes amylase, trypsinogen, exopeptidase and lipase
• Liver secretes bile which emulsifies lipids
• Brunner's glands:

  • secretes alkaline mucus/juice
  • neutralises stomach acid
  • provides optimum pH for enzymes
  • protects the duodenum wall
• Enterokinase is secreted into the duodenum by glands in the mucosa. It activates trypsinogen into trypsin to prevent autolysis.
• Intracellular digestion occurs inside the cells e.g. in the membranes of the microvilli epithelial cells. All dimer to monomer digestion occurs here.
• Duodenum:

  The liver

  • the liver produces bile. This bile is stored in the gall bladder from where it can enter into the duodenum via the bile duct

  Bile

  • emulsifies lipids into smaller droplets. This increases the surface area of the lipid droplets which increases the rate of digestion
  • aids in neutralising the stomach acid as it enters the duodenum with the food
• Duodenum:

  The pancreas

  • the exocrine glands in the pancreas secrete pancreatic juice. This juice enters the duodenum via the pancreatic duct.
  • It contains these enzymes:
  • endopeptidases - hydrolyse protein to polypeptides. Trypsin is secreted in an inactive form called trypsinogen which s activated by enterokinase
  • exopeptidases - hydrolyses the terminal ends of a polypeptide into dipeptides and amino acids
  • amylase - hydrolyses any remaining starch to maltose
  • lipase - hydrolyses lipids to fatty acids and glycerol
• Duodenum:

  • the duodenum makes up the first 20cm of the small intestine
  • it receives secretions from the liver and the pancreas
  • Aid in digestion:
  • Brunner's glands in the submucosa secrete mucus for lubrication and protection, and alkaline juice which helps maintain the optimum pH for the functioning of the enzymes in this area
  • Intracellular chemical digestion:
  • carbohydrate and protein digestion is completed by enzymes fixed in the membrane of the epithelial cells of the mucosa
• autolysis - self digestion of proteins in your own cells
• Extracellular digestion occurs outside of cells e.g. in the lumen of the gut