Digestion

• mouth - physical - teeth - cut+crush food
• salivary glands - chemical - produces saliva containing amylase, lubricates the bolus
• oesophagus -pushes food into stomach
• stomach

  • physical - muscles contract
  • chemical - hydrochloric acid, protease
• liver

  • chemical - produces bile - neutralises HCl, emulsifies fats
• gall bladder

  • chemical - stores bile
• pancreas

  • chemical - produces pancreatic amylase
• small intestine (ileum) - absorbs amino acids, nutrients, etc
• large intestine (colon) - water + vitamin absorbtion
• physical digestion:

  • mechanical breakdown of large food stuffs to make smaller pieces
  • increases surface area for chemical digestion
• chemical digestion:

  • use of chemical reactions to hydrolyse bonds in macromolecules
  • makes molecules small enough to be absorbed by membranes
• Protein digestion - endopeptidase:

  • breaks bond in middle of chain
  • produced in stomach -> function in stomach
  • produced in pancreas -> function in ileum
  • produces shorter polypeptides
• protein digestion- exopeptidase

  • breaks bond on outside of chain
  • produced in stomach -> function in stomach
  • produced in pancreas -> function in ileum
  • produces either
  • amino acid+shorter polypeptide
  • dipeptide + shorter polypeptide
• protein digestion- membrane-bound dipeptidase

  • breaks bond between 2 amino acids
  • located in small intestine
  • produces 2 amino acids
• features of the ileum:

  Membrane-bound disaccharidases + dipeptidases

  • digest disaccharides and dipeptides to form monosaccharides and amino acids, which are small enough to be absorbed through channel and carrier proteins in the cell surface membrane
• features of the ileum:

  Rugae (folds in wall of ileum)

  • increases surface area of the walls for a faster rate of absorption of the products of digestion
• features of the ileum:

  Villi

  • increases surface area + contains enzymes
• features of the ileum:

  Epithelial cell

  • lining of ileum is only one cell thick, providing a short diffusion pathway
• features of the ileum:

  Microvilli

  • increases surface area
• features of the ileum:

  Mitochondria

  • more respiration produces more ATP, so more active transport can occur into the cell
• Lipid digestion:

  • lipids form droplets to repel water - hydrophobic
  • bile salts emulsify the droplets
  • after fusion with bile salts, droplets are called micelles
  • micelles release contents at the membrane of epithelial cells in ileum
  • monoglycerides and fatty acids from micelles are lipid-soluble, so cross by simple diffusion
  • SER synthesises these into triglycerides, which are packaged into vesicles with proteins, forming chylomicrons
  • contents of chylomicrons leave cells via exocytosis as they are large
• Lipid digestion:

  Bile salts can interact with lipids as they are amphipathic - they have a polar region and a non-polar region.