Question

Blood glucose levels are under the control of the hormones insulin and glucagon. Describe the control of blood glucose levels in a (normal) individual following a carbohydrate meal.

Answer 1

Normal blood glucose level is very important in the sound functioning of human body. This is achieved by a highly sophisticated and interrelated network of various hormones and neuropeptides released mainly from the brain, pancreas, liver, intestine as well as adipose and muscle tissues. Within these organs, the pancreas acts as the principal gland by secreting the blood sugar-lowering hormone insulin and its opponent glucagon.

A person before having his breakfast, normally possesses a blood glucose concentration of 80 –90 mg/dL of blood. It may increase to 120–140 mL/dL by one hour after having food. The feedback systems rapidly act to reduce it back to the normal levels, usually within 2 hours after the last absorption of carbohydrates. On the other hand, different mechanisms elevate blood glucose level during starvation.

Insulin and glucagon secreted by islet cells within the pancreas work in balance to regulate the blood sugar levels and to maintain homeostasis. If the level of one hormone is higher or lower than the ideal range, blood sugar levels may spike (hyper glycemia) or drop (hypo glycemia) considerably. When blood sugar is high, insulin is secreted by Beta cells and when blood sugar levels drop, glucagon is released by Alpha cells of pancreas. Insulin helps the cells to absorb glucose from the blood, and to lower the blood sugar level to normal and glucagon helps to turn stored glycogen in the liver back into glucose and release into the blood.

Insulin influences several cells, including muscle, red blood cells, and fat cells. These cells can absorb glucose out of the blood, to lower the high blood glucose levels into the normal range. As blood glucose falls, the amount of insulin secreted by the pancreatic islets goes down.

If blood glucose is high, then no glucagon is secreted and is released into blood when glucose level is reduced. Glucagon acts mainly on cells of liver. Glucagon may activate the enzymes that depolymerize glycogen in the liver and release glucose (glycogenolysis), promoting glucose release by the liver and adipose tissue. Glucagon can reduce the rate of glucose breakdown (by reducing cell respiration rates) and induce the liver and muscle cells to make glucose out from non-carbohydrate precursors as protein (gluconeogenesis) .