3. 3.1 List three hormones that are elevated in the blood following a carbohydrate rich diet. (20 marks)

3.2 Select one of the hormones listed in

3.1 that acts on hepatocytes and describe insulin mode of action in hepatocyte for the maintenance of the blood glucose level. (40 marks)

3.3 Explain the role played by epinephrine in providing the energy for myocyte during exercise. (40 marks)

3.1

Insulin

Insulin like growth factor-1

GTP

Insulin Mode of Action

3.2 Insulin- which is a peptide hormone Is a secreted by pancreatic β cells is transported via blood to target tissues like skeletal muscles, adipocytes, liver etc. As it’s water soluble protein it act via 2nd messenger system. Insulin mode of action via tyrosine kinase receptor. It has 2 subunits namely α subunit and β subunit. α subunit contains hormone binding suite in ECF. β subunit contain 2 parts. Hydrophobic domain which is embedded in cytoplasm and a cytosolic domain which contain tyrosine kinase enzyme.

Once the hormones binds to receptor; Tyrosine kinase of cytosolic domain get phosphorylated. This will result in subsequent phosphorylation of intracellular proteins like IRS and protein kinase B. Finally this will promote gene transcription of glucokinase and other enzymes.

Glucokinase is the main regulatory enzyme of glycolytic pathway which occur n liver. As it has a less affinity than hexokinase it can trap move glucose as glucose-6-phosphate. This is helpful in increasing glucose uptake in the liver which will result in reduction of blood glucose levels.

Also it will increase synthesis of phosphofructokinase-1 and pyruvate kinase which are regulatory enzymes of glycolysis. This will result in increase glycolysis.

Also it increases glycogen synthesis by activating glycogen synthase. Inhibit gluconeogenesis & glycogenolysis.

Adenyl Cyclase action of Epinephrine

3.3 During exercise sympathetic nervous system gets activated and it will cause release of epinephrine.

Epinephrine is a catecholamine which is secreted by adrenal medulla it acts via 2nd messenger system as it is a water soluble hormone. It binds to G protein coupled receptors on the surface of myocytes. It will increase cAMP by activating adenyl cyclase.

cAMP activate protein kinase A activate glycogen phosphorylase and other enzymes in glycolytic pathway in nucleus. It will increase glycogenolysis. Glucose-6-phosphate thus produced as an end product will enter glycolytic pathway and produce ATP. This will provide more energy for exercise.



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