regulation of blood glucose concentration

• Blood glucose concentration can increase as a result of:

  • diet
  • glycogenolysis
  • gluconeogenesis
• Glycogenolysis = glycogen stored in the liver and muscle cells is broken down into glucose which is released into the bloodstream.
• Gluconeogenesis = the production of glucose from non-carbohydrate sources (e.g. glycerol and amino acids)
• Blood glucose concentration can be decreased by:

  • Respiration
  • Glycogenesis
• Glycogenesis = the production of glycogen from glucose
• Insulin secretion:

  • when blood glucose rises, glucose enters the beta cell
  • glucose is metabolised, inside the mitochondria, resulting in the production of ATP
  • ATP binds to potassium channels causing them to close
  • depolarisation occurs
  • depolarisation causes voltage-gated calcium channels to open
  • calcium ions enter the beta cell and cause vesicles to release the inulin they contain by exocytosis
• Insulin lowers blood glucose concentration by:

  • increasing rate of absorption of glucose by cells
  • increasing respiratory rate of cells
  • increasing rate of glycogenesis
  • increasing rate of glucose to fat conversion
  • inhibiting the release of glucagon
• Insulin is broken down by enzymes in the cells of the liver. Therefore, to maintain its effect it has to be constantly secreted.
• As blood glucose concentration returns to normal, this is detected by the beta cells of the pancreas and they reduce their secretion of insulin. This is an example of negative feedback.
• Glucagon is produced by the alpha cells of the islets of Langerhans in the pancreas. If the blood glucose concentration is too low, the alpha cells detect this fall and secrete glucagon directly into the bloodstream.
• Unlike insulin, the only cells in the body which have glucagon receptors are the liver cells and fat cells - therefore these are the only cells that can respond to glucagon.
• Glucagon raises blood glucose concentration by:

  • glycogenolysis
  • reducing the amount of glucose absorbed by the liver cells
  • increasing gluconeogenesis