Regulation of blood glucose conc. part 2

Question 1

Where is glucagon produced?

Answer 1

by the alpha cells of the islets of Langerhans in the pancreas

Question 2

How is glucagon secreted and received?

Answer 2

• if the blood glucose conc. is too low, the alpha cells detect this fall and respond by secreting glucagon directly into the bloodstream
• • there are only two cells in the body which have glucagon receptors - liver cells and fat cells - therefore these are the only cells that can respond to glucagon

Question 3

How does glucagon raise blood glucose concentration?

Answer 3

• glycogenolysis - the liver breaks down its glycogen store into glucose and releases it back into the bloodstream
• reducing the amount of glucose absorbed by the liver cells
• increasing the gluconeogenesis - increasing the conversion of amino acids and glycerol into glucose in the liver

Question 4

How is glucagon secretion stopped?

Answer 4

• same as beta cells
• • negative feedback causes the corrective measures to be switched off, returning the system to its original level

Question 5

How is the system of maintaining blood glucose concentration self-regulation?

Answer 5

• the level of glucose in the blood determines the quantity of insulin and glucagon that is released

Question 6

What is the mechanism for the secretion of insulin?

Answer 6

• at normal blood glucose conc. levels, potassium channels in the plasma membrane of beta cells are open and potassium ions diffuse out of the cells, the inside of the cells is at a potential of -70mV with respect to the outside of the cell
• when blood glucose concentration rises, glucose enters the cells by a glucose transporter
• the glucose is metabolised inside the mitochondira, resulting in the production of ATP
• the atp binds to potassium channels and causes them to close - aka ATP-sensitive potassium channels
• potassium ions can no longer diffuse out of the cells, the pd reduces to -30mV - depolarisation occurs
• depolarisation causes the voltage-gated calcium channels to open
• calcium ions enter the cells and cause secretory vesicles to release the insulin they contain by exocytosis