Question

Compare and contrast the molecular and cellular activities of Insulin and Glucagon on different tissues (adipose, skeletal muscle – resting & active, liver, pancreas) during fed and fasting metabolisms. [Include stimuli for secretion, source tissues, target cells, and cellular mechanisms of action.]

Answer 1

Glucose homeostasis is maintained mainly by 2 Hormones Insulin and Glucagon.

INSULIN-

Insulin is the hormone secreated by Beta cells of islets of langherhans of pancreas that reduces blood glucose level.

After a Meal (when blood glucose level is Increased ≥ 3 mmol/L)insulin is released. The stimulus for insulin secretion is a HIGH blood glucose, insulin secretion is regulated by various hormones, such as melatonin, estrogen, leptin, growth hormone, and glucagon like peptide-1 .

Insulin lowers blood glucose by -

1.MUSCLES AND ADIPOSE TISSUES-

*Increasing glucose uptake in muscle and adipose tissue by increasing the number of plasma membrane GLUT1 and GLUT4.

2.LIVER-

*Promoting glycolysis and glycogenesis in liver

*Reducing hepatic glucose output(Glycogenolysis and glucogenesis).

3.KIDNEY-

Insulin in kidney causes -

*Reduces renal gluconeogenesis thus reducing glucose release into circulation.

*Stimulates renal Glucose uptake

GLUCAGON-

Glucagon is the hormone released by Alpha cells of islets of langherhans of Pancreas.This Hormone increases the Blood Glucose level.

Glucagon secretion is stimulated by low blood glucose concentrations (hypoglycemia), by the ingestion of protein,and by exercise.

1.ADIPOSE TISSUE-

*Increases the release of glycerol from adipose tissue ,from which glucose can be formed in the liver.

2.LIVER-

*. stimulating gluconeogenesis and glycogenolysis

*decreases glycogenesis and glycolysis in the liver

{Glycogenolysis is the process by which Glycogen is metabolised in to Glucose & Gluconeogenesis is the process in which new glucose molecules are synthesized from non carbohydrate sources.
Glycogenesis is the formation of glycogen from glucose and Glycolysis  is pathway in which glucose is converted into Pyruvate}

3.TISSUES -

*Promotes lipolysis in these tissues, in which fatty acids are released into circulation where they can be catabolised to generate energy in tissues such as skeletal muscle when required.There by sparing Use of glucose for energy during Low Glucose In the Body