Blood glucose control 1

Question 1

Describe the mode of action of hormones.

Answer 1

Hormones are produced in endocrine glands and are secreted into the blood. They are carried in the blood plasma to all cells. They only act on target cells due to specific receptors on their cell surface membrane.
They are effective at low concentrations and can have widespread and long lasting effects.

Question 2

Why is it important to maintain blood glucose concentration within restricted limits?

Answer 2

• Provides a constant availability of a respiratory substrate
• to maintain the water potential of the blood and therefore cells

Question 3

Describe the second messenger model for adrenaline and glucagon.

Answer 3

Adrenaline/glucagon binds to the protein receptor in the membrane of a liver cell. The binding causes the protein to change shape on the inside of the membrane. This change of shape activates the enzyme adenyl cyclase which converts ATP to cAMP. The cAMP acts as the second messenger and binds to the enzyme protein kinase, changing the shape, activating it. The protein kinase catalyses the hydrolysis of glycogen into glucose. This increases blood glucose.

Question 4

Describe glycogenesis.

Answer 4

The conversion of glucose into glycogen using a condensation reaction to form a glycosidic bond.

Question 5

Explain how the production of glycogen in liver cells lowers blood glucose levels.

Answer 5

Glucose level in the liver cell falls creating a concentration gradient with the blood. Glucose enters the liver cells from the blood down the concentration gradient via facilitated diffusion.

Question 6

Describe glycogenolysis.

Answer 6

The hydrolysis of glycogen into glucose.

Question 7

Explain when glycogenolysis will occur and what happens

Answer 7

When blood glucose levels fall and the alpha cells in the islets of Langerhans detect the change they release glucagon. Glucagon is received by the liver cells and the second messenger cAMP activates protein kinase to catalyse glycogen into glucose. This raises the blood glucose level

Question 8

Describe gluconeogenesis.

Answer 8

The production of glucose from glycerol or amino acids. It increases blood glucose. It occurs in response to the hormone glucagon.

Question 9

Describe the role of insulin in blood glucose control.

Answer 9

Binds to receptors on the cell surface membrane of liver and muscle cells. Increases the number of channel proteins in the surface membrane. This increases the rate of facilitated diffusion of glucose into cells. Insulin also causes the activation of enzymes involved in the conversion of glucose to glycogen.

Question 10

Explain why the action of glucagon is classed as negative feedback

Answer 10

• The decrease in blood glucose caused the release of glucagon from the alpha cells which brings about corrective mechanism which restore blood glucose to within normal levels. This then inhibits the release of glucagon
• The release of glucagon caused inhibition of its own release.