Introduction to blood sugar regulation

Question 1

What are the 3 major cells in the Islets of Langerhans and what do they secrete?

Answer 1

Alpha cells (secrete glucagon)
Beta cells (secrete insulin and amylin)
Delta Cells (secrete somatostatin)

Question 2

What are the 2 main hormones which control blood glucose levels?

Answer 2

Insulin - used to reduce blood glucose

Glucagon - used to increase blood glucose

Question 3

How does insulin lower blood glucose levels - 4 steps

Answer 3

• Insulin binds to insulin receptors on cell surface of cell membranes such as muscle and adipose
• Causes intracellular storage vesicles containing GLUT 4 to fuse with cell membrane
• GLUT4 proteins embed into the membrane and allow glucose to move into the cell
  This lowers blood glucose levels

Question 4

What raises blood glucose levels?

Answer 4

Glucagon

Question 5

How does glucagon raise blood glucose levels? - Long answer Q

Answer 5

• Alpha cells in pancreas islets are sensitive to glucose concentrations in blood
• When glucose levels are low, alpha cells secrete glucagon into blood
• Glucagon also secreted by adrenaline during stressful situations
• Glucagon binds to glucagon receptor in membrane of target cells (mainly liver and also adipose)
• When bound, glucagon promotes the breakdown of glycogen into glucose and fatty acids
  1. In liver = glycogen into glucose (glycogenolysis) and
  2. Glucose from lactic acid and non carbohydrate molecules (gluconeogenesis)
  3. Effect on fat = breakdown of fat (lipolysis) releasing fatty acids as energy source

Glucose released into blood = increase in blood glucose