Controlling blood glucose concentration

• What are the three ways glucose can enter the bloodstream?

  Absorption in the gut, hydrolysis of glycogen stores, and conversion of non-carbohydrates to glucose
• How does the amount of glucose absorbed from digestion vary?

  It can vary substantially based on the carbohydrate content of the food
• What hormones are involved in managing blood glucose concentration?

  Insulin and glucagon
• What happens to excess glucose in the blood after a carbohydrate-dense meal?

  It is removed through increased glucose uptake and glycogenesis
• What occurs when there is insufficient glucose in the blood?

  Glucose is rapidly released from storage molecules
• What is the role of insulin and glucagon in blood glucose regulation?

  They are constantly regulated to maintain blood glucose concentration
• What is the consequence of blood glucose concentration decreasing below a certain level?

  Cells may not have enough glucose for respiration
• What happens if blood glucose concentration increases above a certain level?

  It can disrupt normal cell function
• What is the key part of homeostasis related to blood glucose concentration?

  The control of blood glucose concentration
• What are the two cell types found in the Islets of Langerhans?

  Alpha cells and beta cells
• What hormone do alpha cells secrete?

  Glucagon
• What hormone do beta cells secrete?

  Insulin
• How do alpha and beta cells respond to a decrease in blood glucose concentration?

  Alpha cells secrete glucagon, and beta cells stop secreting insulin
• What is the first step when glucagon binds to liver cell receptors?

  It causes a conformational change that activates a G protein
• What does active adenylyl cyclase do?

  It catalyzes the conversion of ATP to cyclic AMP (cAMP)
• What is the role of cAMP in the signaling pathway initiated by glucagon?


  It activates protein kinase A enzymes
• What does active protein kinase A do?

  It activates phosphorylase kinase enzymes
• What is glycogenolysis?

  The breakdown of glycogen to glucose
• How does glucagon amplify the original signal?

  Through an enzyme cascade that releases extra glucose
• What role does adrenaline play in blood glucose concentration?

  It increases blood glucose by activating the same enzyme cascade as glucagon
• What happens when blood glucose concentration increases above normal?

  Beta cells in the pancreas detect it and secrete insulin
• How do glucose molecules enter beta cells when glucose concentration is high?

  By facilitated diffusion
• What effect does high ATP concentration have on potassium channels in beta cells?

  It causes the potassium channels to close
• What happens when voltage-gated calcium channels open in beta cells?

  Calcium ions influx leads to insulin secretion
• What is the action of insulin on target cells?

  It stimulates the uptake of glucose by muscle, fat, and liver cells
• What are glucose transporter proteins?

  Proteins that facilitate glucose uptake in target cells
• How does insulin increase glucose uptake in target cells?

  By activating more glucose transporter proteins on their surface
• What is glycogenesis?

  The synthesis of glycogen from glucose molecules
• How does insulin affect glucose concentration in the liver?

  It stimulates glycogenesis, lowering glucose concentration
• What is gluconeogenesis?

  The synthesis of glucose from non-carbohydrate molecules
• What triggers gluconeogenesis?

  Glucagon activates enzymes that convert non-carbohydrates into glucose
• What are the negative feedback control mechanisms in blood glucose regulation?

  • Receptors detect glucose levels (alpha and beta cells in pancreas)
  • Hormonal or nervous system communicates information to effectors
  • Effectors react to counteract changes:
  • Alpha cells release glucagon
  • Beta cells release insulin
  • Liver cells respond to glucagon
  • Liver, muscle, and fat cells respond to insulin
• What are the processes triggered by insulin and glucagon in the liver?

  • Insulin triggers glycogenesis (synthesis of glycogen)
  • Glucagon triggers glycogenolysis (breakdown of glycogen)
  • Glucagon also triggers gluconeogenesis (synthesis of glucose from non-carbohydrates)
• What is the role of the liver in blood glucose regulation?

  • Converts glycogen to glucose and vice versa
  • Responds to insulin and glucagon
  • Maintains blood glucose concentration within a normal range
• What is the significance of glucose transporter proteins in insulin action?

  • Facilitate glucose uptake in target cells
  • Their number is increased by insulin binding to receptors
  • Increase the permeability of cells to glucose
• What is the enzyme cascade initiated by glucagon in liver cells?

  1. Glucagon binds to liver cell receptors
  2. Activates G protein
  3. Activates adenylyl cyclase
  4. Converts ATP to cAMP
  5. Activates protein kinase A
  6. Activates phosphorylase kinase
  7. Activates glycogen phosphorylase
  8. Glycogen is broken down to glucose
• What are the effects of adrenaline on blood glucose concentration?

  • Increases blood glucose concentration
  • Activates the same enzyme cascade as glucagon
  • Stimulates glycogen breakdown in muscle during exercise