Digestion and absorption

• ileum :

  very long

  internal lining is folded - provides larger surface area

  has villi and microvilli
• Villi : finger-like projections that cover the surface of an ileum's fold
• Microvilli: microscopic projections that line the epithelial cells of the villi
• Villi

  • increase surface area
  • thin walled
  • have muscle cells so they can move
  • well supplied with blood vessels
• co-transport is the coupled movement of substances across a cell membrane via a carrier protein
• Trilycerides can be found in the gut lumen and in the epithelial cells
• Triglycerides are emulsified into micelles by bile salts
• Micelles are non-polar molecules
• In the epithelial cells , monoglycerides and fatty acids are transported to the Endoplasmic rectilium to recombine into triglycerides
• Trilycerides associate cholesterol and lipoproteins to form chylomicrons
• Chylomicrons move out of the epithelial cells by exocytosis and enter the lacteals at the centre of the vili .
• exocytosis is the process of cell transport and releasing substances from inside the cell to the outside
• Monitoring the products of digestion :

  • blood carrying the products of digestion leaves the villus and travels along the hepatic portal vein to the liver
  • liver monitors and regulates levels of the product in the blood
• Digestion is when large biological molecules are hydrolysed into smaller molecules that can be absorbed across cell membranes into the blood stream
• Haemoglobin has four polypeptide chains
• each polypeptide chain in haemoglobin is bound to a prosthetic group called haem
• the oxygen dissociation curve measures the amount of oxygen that combines with haemoglobin
• because oxygen is a gas we dont say concentration , we say partial pressure
• affinity means how strongly the oxygen is bound to the haemoglobin
• each haem group binds to one oxygen molecule
• The Bohr affect: carbon dioxide causes the oxygen affinity of haemoglobin to decrease
• carbon dioxide can form the acidic molecule carbon acid
• carbonic acid releases the hydrogen ion
• hydrogen ion combines with haemoglobin and causes it quaternary structure to change and have a lower affinity for oxygen