Explain the Regulation of Blood Glucose Concentration?

A number of mechanisms function to maintain blood glucose at remarkably constant level of 70-100 mg/dl under fasting conditions. Regulation is the net effect of the organ's metabolic processes that remove glucose from the blood for either glycogen synthesis or for energy release and of processes that return glucose to the blood, such as glycogenolysis and gluconeogenesis. Let us understand both of these mechanisms of blood glucose regulation.

Figure illustrates the regulatory process

After a meal, when blood glucose levels increase, the peptide hormones (such as cholecystokinin) secreted from enteroendocrine cells within the mucosa of the small bowel amplify the response of the β-cells of pancreas resulting in the secretion of insulin. Insulin facilitates the transport of glucose by glucose transporter - GLUT 4 into the adipocytes and muscle cells and stimulates glycogenesis (synthesis of glycogen) and fatty acid biosynthesis, thus returning the blood glucose to homeostatic level.

This was the case when there are high glucose levels in blood. But what happens, when the level of glucose falls? How, then the energy demands of cells are met? Well, in case of post absorptive state, the fall in blood glucose level signals the reversal of the pancreatic hormonal secretion i.e. decreased insulin and increased glucagon release. Blood glucose levels are maintained by the breakdown of glycogen and in this way, the glucose demands of brain, RBCs and testis are met. In long periods of fasting' or starvation, glucose is supplied from non-carbohydrate sources by gluconeogenesis. Glucose is synthesized from a range of substrates including pyruvate, lactate, glycerol and amino acids. Body proteins are catabolized to release amino acids while triacylglycerol yields glycerol. These gluconeogenic processes are triggered by a fall in blood glucose concentration below 5.0 mmol (90 mg/dl) and are signaled to the tissues by the secretion of glucagon and glucocorticoid hormones.