blood glucose

• Homeostasis


  The maintenance of a constant internal environment
• Negative feedback


  Any deviation from the normal limits or values are restored to their original level
• Blood glucose levels


  An example of negative feedback
• Pancreas


  • The key organ involved in controlling blood glucose levels
  • Contains endocrine cells (islets of Langerhans) that release insulin and glucagon
• Insulin


  A hormone released by the pancreas that causes liver cells to become more permeable to glucose and enzymes to convert glucose to glycogen
• Glucagon


  A hormone released by the pancreas that activates enzymes to hydrolyse glycogen back into glucose
• Adrenaline

  A hormone released by the adrenal glands that also increases blood glucose levels, but is not part of the negative feedback loop
• Negative feedback loop for increasing blood glucose levels

  1. Increased blood glucose detected by beta cells

  2. Beta cells release insulin

  3. Insulin causes liver to absorb glucose and convert to glycogen

  4. Blood glucose levels return to normal
• Negative feedback loop for decreasing blood glucose levels

  1. Decreased blood glucose detected by alpha cells

  2. Alpha cells release glucagon

  3. Glucagon causes liver to break down glycogen into glucose

  4. Blood glucose levels return to normal
• Glycogenesis


  The process of excess glucose being converted to glycogen
• Glycogenolysis

  The process of glycogen being hydrolysed back into glucose
• Gluconeogenesis

  The process of creating new glucose from non-carbohydrate sources like amino acids
• How insulin increases blood glucose levels


  1. Insulin binds to receptors on liver cells

  2. Causes channels to open and more to be incorporated into cell membrane

  3. Allows more glucose to diffuse into cells

  4. Enzymes convert glucose to glycogen
• Second messenger model for glucagon and adrenaline


  1. Hormone binds to receptor

  2. Activates adenylate cyclase enzyme

  3. Converts ATP to cyclic AMP (second messenger)

  4. Activates protein kinase enzyme

  5. Enzyme hydrolyses glycogen to glucose
• Type 1 diabetes


  Inability to produce insulin, typically starts in childhood, treated with insulin injections
• Type 2 diabetes


  Reduced responsiveness of cells to insulin, typically develops in adulthood, treated by controlling carbohydrate intake and increasing exercise