The small intestine

• how many regions does the small intestine have?

  2
• what are the 2 regions of the small intestine?

  • duodenum
  • ileum
• what does relaxation of the pyloric sphincter muscle at the base of the stomach allow?

  it allows partially digested food into the duodenum, a little at a time
• how much of the small intestine is the duodenum?

  the duodenum is the first 25 cm
• where are the secretions that the duodenum receives from?

  from the liver and the pancreas
• where is bile made?

  in the liver
• where is bile stored?

  in the gallbladder then passes through the bile duct into the duodenum
• what does bile contain?

  • it doesn’t contain enzymes
  • it contains bile salts, which are amphipathic (i.e. their molecules have hydrophilic and hydrophobic parts - they emulsify lipids in the food by lowering their surface tension and breaking up large globules into smaller globules, which increases their surface area, making digestion by lipase more efficient
• what is the pH of bile like and what does it do?

  • its alkaline and neutralises the acid in food coming from the stomach
  • it provides a suitable pH for the enzymes in the small intestine
• what is pancreatic juice?

  • its secreted by islet cells, which are exocrine glands in the pancreas
  • it enters the duodenum through the pancreatic duct
• where do exocrine glands secrete enzymes into?

  into ducts
• where do endocrine glands secrete hormones into?

  directly into the blood
• what are the enzymes involved in pancreatic secretion?

  • trypsinogen
  • endopeptidases
  • amylase
  • lipase
• what does trypsinogen do?

  inactive enzyme converted into the endopeptidase trypsin by the duodenal enzyme, enterokinase
• what does endopeptidases do?

  hydrolyse proteins and polypeptides to peptides
• what does amylase do?

  digests any remaining starch to maltose
• what does lipase do?

  hydrolyses lipids into fatty acids and monoglycerides
• what does sodium hydrogen carbonate do in pancreatic secretion?

  raises the pH to make pancreatic juice slightly alkaline and contributes to:

  • neutralising acid from the stomach
  • providing the appropriate pH for the pancreatic enzymes to work efficiently
• what is this an image of?

  the duodenum, gall bladder and liver

  
• what is the food coming from the stomach lubricated and neutralised by?

  by mucus and neutralised by alkaline secretions from cells at the base of the crypts of Lieberkühn, called Brunner’s glands
• what do the epithelial cells lining the ileum have?

  they have finger-like projections called villi which synthesis digestive enzymes
• where are endopeptidases and exopeptidases secreted from and what do they do?

  • peptidases are secreted by villus epithelial cells and digestion continues in the gut lumen
  • dipeptidases in the cell surface membranes digest dipeptides to amino acids
• what do carbohydrases do?

  • they are secreted and digestion continues in the gut lumen
  • carbodhydrases in the cell surface membranes digest disaccharides into monosaccharides
  • some disaccharides are absorbed so their digestion is intracellular