3.6.4.2 Control of blood glucose concentration

• How is blood glucose regulated?

  • Insulin lowers blood glucose by promoting uptake and glycogenesis.
  • Glucagon raises blood glucose by stimulating glycogenolysis and gluconeogenesis.
• Insulin lowers blood glucose by increasing cellular uptake and promoting glycogenesis (conversion of glucose to glycogen in the liver).
• Glucagon raises blood glucose by stimulating glycogenolysis (breakdown of glycogen to glucose) and gluconeogenesis (formation of glucose from non-carbohydrates).
• Explain how negative feedback regulates blood glucose levels.

  • High glucose triggers insulin release to lower levels.
  • Low glucose triggers glucagon release to raise levels, maintaining homeostasis.
• Adrenaline raises blood glucose by stimulating glycogen breakdown and inhibiting glycogen synthesis.
• How does type 1 diabetes affect blood glucose regulation?

  • The pancreas fails to produce insulin, causing high blood glucose levels.
  • Treatment involves insulin injections.
• How does type 2 diabetes affect blood glucose regulation?

  • Cells become resistant to insulin, impairing glucose uptake.
  • Treatment involves diet, exercise, and medication.
• Gluconeogenesis is the process of producing glucose from non-carbohydrate sources, such as amino acids and glycerol.
• Glycogenesis is the process of converting glucose into glycogen for storage in the liver and muscles.
• Glycogenolysis is the breakdown of glycogen into glucose to increase blood sugar levels. This primarily occurs in the liver and muscle cells.
• Insulin is secreted by beta cells of the pancreas when blood glucose levels are high.
• Glucagon is secreted by alpha cells when blood glucose is low.
• Explain the effects of adrenaline on blood glucose levels during the fight-or-flight response.

  • Adrenaline is released during the fight-or-flight response
  • It promotes glycogenolysis in the liver and muscles, increasing blood glucose levels for quick energy
  • It inhibits insulin secretion to prevent glucose storage, ensuring glucose remains available for immediate use.
• In type I diabetes, the immune system attacks and destroys beta cells in the pancreas, leading to insufficient insulin production.
• The islets of Langerhans are in the pancreas.
• The pancreas contains clusters of cells called islets of Langerhans that produce hormones to regulate blood glucose.

  • Alpha cells: secrete glucagon.
  • Beta cells: secrete insulin.
• Effects of Glucagon:

  1. Stimulates glycogenolysis: Stimulates the liver to break down stored glycogen into glucose.
  2. Stimulates gluconeogenesis: Stimulates the liver to produce new glucose from amino acids and glycerol.
  3. Reduces glucose uptake by cells: Reduces the uptake of glucose by muscle and fat cells, ensuring glucose remains in the bloodstream.
• The control of blood glucose concentration follows a negative feedback loop.
• When blood glucose rises (e.g., after eating):

  • Stimulus: Blood glucose concentration increases.
  • Receptor: Detected by the pancreas (specifically, the beta cells).
  • Control centre: Beta cells in the pancreas release insulin.
  • Effector: Insulin acts on liver, muscle, and fat cells.
  • Response: Glucose is taken up by cells, and glycogen is stored in the liver, lowering blood glucose back to normal levels.
• When blood glucose falls (e.g., between meals or after exercise):

  • Stimulus: Blood glucose concentration decreases.
  • Receptor: Detected by the pancreas (specifically, the alpha cells).
  • Control centre: Alpha cells in the pancreas release glucagon.
  • Effector: Glucagon acts on the liver.
  • Response: Glycogen is broken down into glucose and released into the blood, raising blood glucose back to normal levels.
• What is blood glucose concentration?

  The amount of glucose in the blood, regulated to maintain energy balance for cellular function.
• Why is it important to regulate blood glucose?

  To prevent hyperglycemia (high glucose, which damages blood vessels) and hypoglycemia (low glucose, leading to confusion and unconsciousness).
• The primary role of insulin in glucose regulation is to promote glucose uptake and glycogen storage.
• Glucagon stimulates gluconeogenesis.
• Adrenaline acts as a secondary messenger in the break down of glycogen into glucose to raise blood glucose levels.
• Adrenaline is a hormone secreted by the adrenal medulla, a part of the adrenal glands, in response to stress or low blood glucose levels. It helps prepare the body for rapid action in "fight or flight" situations.
• Adrenaline increases blood glucose levels by:

  1. Stimulating glycogenolysis
  2. Inhibiting glycogenesis
  3. Promoting gluconeogenesis
• How does adrenaline act as a secondary messenger?

  • it fuses to a receptor on the cell surface membrane of the liver cell and causes the receptor to change shape on the inside of the membrane
  • this activates the enzyme adenyl cyclase which converts ATP to cyclic AMP (cAMP) - acts as a second messenger
  • cAMP then changes shape and activates protein kinase enzyme which catalyses the conversion of glycogen into glucose