Hormones and regulation of blood glucose

• Hormones are produced by endocrine glands and secreted directly into the bloodstream
• Hormones bind to receptors on the target cells because they are complementary
• Hormones are produced in small quantities but have widespread and long-lasting effects
• Modes of Action

  1. Activation of cell-surface receptors
  2. Diffuse directly into cells through the phospholipid bilayer
  3. Second-messenger systems
• Second-messenger systems

  • binds to receptor on plasma membrane
  • adenylate cyclase activated
  • ATP synthesised to cAMP
  • activates protein kinase
• Increase in blood glucose concentration

  1. Detected by pancreas which secretes insulin from beta cells
  2. Insulin binds to receptors on muscle + liver cells
  3. This increases the number of glucose channel proteins in the cell-surface membrane
  4. This also activates enzymes for glycogenesis
  5. Blood glucose concentration decreases
• Decrease in blood glucose concentration

  1. Detected by pancreas which secretes glucagon from alpha cells
  2. Glucagon binds to receptors in liver cells and acts via second messenger
  3. This activates enzymes for glycogenolysis and gluconeogenesis
  4. Blood glucose concentration increases
• Adrenaline

  1. Secreted by adrenal glands when blood glucose concentration is low
  2. Adrenaline binds to receptors on liver cells and acts via second messenger
  3. Activates enzymes for glycogenolysis
  4. Blood glucose concentration increases