5.4.4(Regulating blood glucose)

State 3 things which cause blood glucose levels to increase

1. Absorption in the gut following carbohydrate digestion

2. Hydrolysis of glycogen stores

3. Non-carbohydrates such as lipids, lactate and amino acids that have been converted to glucose

Describe the action of insulin in controlling blood glucose concentration

• Blood glucose rise which is detected by beta cells in the islets of Langerhans causing them to secrete insulin

• Insulin travels in the blood to muscle and liver cells mainly

• Insulin binds to specific receptors on the plasma membrane

• This causes the activation of tyrosine kinase which is associated with the receptor inside the cell

• Tyrosine kinase causes the phosphorylation of inactive enzymes in the cell

• This causes the activation of enzymes which cause vesciles containing glucose transporter proteins to fuse with the membrane

• This causes more glucose to enter the target cell by facilitated diffusion which causes a cascade of reactions in the cell

State the 1 type of cell which does not have Insulin receptors on its plasma membrane

• erythrocytes

Describe the effect of insulin in cells

• Glucose in the cell is converted into glycogen(Glycogenesis)

• Glycolysis increased, respiratory rate increased

• If glycogen stores are adequate then glucose is converted into fat in the liver and adipose tissue(lipogenesis)

Describe the response to blood glucose levels being too low

• It is detected by alpha cells in the islets of Langerhans which then secrete glucagon

• Glucagon is secreted into the blood and travels to the liver and muscles

• Glucagon binds to receptors on plasma membrane specific and complementary to glycogen

• This causes the stimulation of G-proteins which causes the activation of adenyl cyclase inside the cell

• Which converts ATP to cAMP which causes the activation of an enzyme cascade

Describe the effect of glucagon in cells

• Second messenger cascade activates conversion of glycogen to glucose - glycogenolysis

• Glucose is also synthesised from amino acids and fats- gluconeogenesis

• Glucose is released into the blood