Controlling blood glucose levels

• Insulin

  • secreted by beta cells
  • secreted when blood glucose is too high
  • binds to specific receptors on liver and muscle cell membranes
• Glucagon

  • secreted by alpha cells
  • secreted when blood glucose is too low
  • binds to specific receptors on liver cell membranes
• Effect of insulin

  • increased permeability of cell membranes to glucose
  • activation of enzymes for glycogenesis (glucose -> glycogen)
  • increases rate of respiration (muscle cells)
• Effect of glucagon

  • activation of enzymes for glycogenolysis (glycogen -> glucose)
  • promotion of gluconeogenesis ( glycerol / amino acids -> glucose)
  • decreases rate of respiration of glucose
• Insulin production in beta cells

  • high glucose concentration -> more enters beta cells via facilitated diffusion
  • results in an increased rate of respiration
  • more ATP is produced, causing ATP sensitive potassium ion channels to close in the plasma membrane
  • K+ builds up inside beta cell
  • voltage sensitive calcium ion channels open, Ca2+ diffuses into the cell
  • docked vesicles containing insulin are released from the cell by exocytosis