Question

Discuss the following: The hormonal regulation of blood glucose and the effect it has on glycolysis, gluconeogenesis, and glycogen metabolism.

Answer 1

The hormonal regulation of blood glucose

Explanation:

When blood glucose levels rise, insulin is secreted by the pancreas, lowering blood glucose by increasing its uptake in cells and stimulating the liver to convert glucose to glycogen, in which form it can be stored.

If insulin secretion is impaired, it can result in diabetes mellitus: a disease in which blood glucose levels remain high, leading to excess glucose in the urine, increased urine output, and dehydration, among other symptoms.

When blood glucose levels fall, glucagon is secreted by the pancreas, which increases blood glucose levels by stimulating the breakdown of glycogen into glucose and the creation of glucose from amino acids.

The basal metabolic rate of the body is controlled by the hormones T3 and T4, produced by the thyroid gland in response to the thyroid stimulating hormone (TSH), produced by the anterior pituitary.

T3 and T4 bind to receptors on the mitochondria, causing an increase in the production of ATP, as well as increase in the transcription of genes that help utilize glucose and produce ATP, resulting in higher metabolismof the cell.

Effect it has on glycolysis:

Glycolysis means sugar (glyco) breaking (lysis). It is an enzymatic pathway which converts glucose (a hexose, six carbon sugar) to two molecules of pyruvate (a triose, 3-carbon sugar). Glycolysis occurs in the cytoplasm and does not require the presence of oxygen. It is found (with variations in the terminal steps), in nearly all organisms and is one of the most ancient known metabolic pathways. In aerobic organisms the pyruvate is used to generate more ATP via the citric acid cycle/cytochrome system, or converted into fatty acids and stored as triglycerides.

Effect on gluconeogenesis:

Gluconeogenesis is a metabolic pathway that results in the generation of glucose from non-carbohydrate carbon substrates such as lactate, all citric acid cycle intermediates (through conversion to oxaloacetate), amino acids other than lysine or leucine, and glycerol.

Gluconeogenesis is one of the two main mechanisms humans and many other animals use to keep blood glucose levels from dropping too low (hypoglycemia). The other means of maintaining blood glucose levels is through the degradation of glycogen (glycogenolysis). Gluconeogenesis takes place mainly in the liver and, to a lesser extent, in the cortex of kidneys. This process occurs during periods of fasting, starvation, low-carbohydrate diets, or intense exercise and is often associated with ketosis. Gluconeogenesis is also a target of therapy for type II diabetes, such as metformin, which inhibits glucose formation and stimulates glucose uptake by cells.

Effect on glycogen metabolism:

Glycogen's role in maintaining blood-glucose levels is especially important because glucose is virtually the only fuel used by the brain, except during prolonged starvation. Moreover, the glucose from glycogen is readily mobilized and is therefore a good source of energy for sudden, strenuous activity. Unlike fatty acids, the released glucose can provide energy in the absence of oxygen and can thus supply energy for anaerobic activity.