NORMAL BLOOD GLUCOSE LEVEL

Maintenance of glucose in fed state* (hyperglycaemic condition)

Normally Blood Sugar level increases after each meal, which can be called Postprandial Hyperglycemia.

Now, this increased blood sugar level releases Insulin hormone by β-cells of Islets of Langerhans from Pancreas.

Insulin reduces Blood sugar level in many ways.

• It stimulates active transport* of Glucose across the cell membrane of muscles & adipose tissues(fat) but not in Liver.
• Because In Liver Glucose is freely permeable so, it is rapidly absorbed.
• In Liver, Insulin increases the use of Glucose by process of Glycolysis by inducing synthesis of key Glycolytic enzymes:

      -Glucokinase

      -Phosphofructokinase

      -Pyruvate kinase.

• In liver & muscles, Insulin stimulates Glycogenesis* (by stimulating Glycogen synthetase enzyme) & so leading to suppression of Glycogenolysis*.
• Insulin inhibits Gluconeogenesis* by suppressing action of key enzymes.
• In adipose tissue, glucose is converted into Glycerol-3-phosphate, which is required for Triacylglycerol (lipogenesis) formation.
• Insulin enhances synthesis of protein & decreases Protein catabolism, so this is how it releases Amino acids.

Maintenance of blood glucose in fasting state (hypoglycemic condition)

When Blood Glucose level decreases, certain Hyperglycaemic Hormones gets released,

e.g.1) Glucagon

      2) Epinephrine/Adrenaline

      3) Glucocorticoids

      4) Growth Hormone & ACTH

      5) Thyroxine.

So, lets learn about them step by step in brief.

1) GLUCAGON

Glucagon is a hormone produced by α-cells if Islets of Langerhans in pancreas.

Its actions are opposite of the actions of Insulin.

It acts primarily on Liver.

• In liver, it stimulates Glycogenolysis by activating enzyme Glycogen Phosphorylase & inhibits Glycogen synthesis.
• Not like Epinephrine, Glucagon doesn’t have effect on muscles due to lack of receptors.
• Glucagon enhances Gluconeogenesis from amino acids & lactic acids by inciting action of Gluconeogenesis.

2) EPINEPHRINE/ ADRENALIN

This hormone is secreted from Adrenal Medulla.

In liver & muscles It stimulates Glycogenolysis.

• In Liver, Glucose is the main product so it leads to increase in Blood Glucose level.
• In muscles, as Glucose-6-phosphatase* enzyme is absent, Glycogenolysis results with the formation of Lactic acid.

3) GLUCOCORTICOIDS

This hormone is secreted from Adrenal Cortex.

It causes Gluconeogenesis by increasing enzyme activities.

It causes catabolism* of Protein to provide glucogenic amino acids for Gluconeogenesis.

It increases absorption of amino acids from liver for Gluconeogenesis.

Glucocorticoids also inhibits the usage of Glucose in extrahepatic tissues.

4) GROWTH HORMONE & ACTH

Its all actions are opposite of Insulin as it increases blood Glucose level.

Growth hormone decreases Glucose uptake in muscles.

ACTH decreases utilization of Glucose by tissues.

5) THYROXINE

A hormone secreted by Thyroid gland.

It increases the rate of Glycogenolysis in liver and causes rise in Blood Glucose level.

It also increases absorption rate of Hexoses from intestine.