Question

An individual has low blood glucose levels—not low enough to cause symptoms, but enough to cause the body to attempt a restoration to normal levels. Describe all processes by which the body induces the increase of blood sugar levels. Your response should include a review of all body cells and structures capable of detecting low glucose levels, the body responses that stimulate glucose production, and all processes for the actual synthesis of glucose. (While this is not a biochemistry class, a thorough discussion of the two major glucose production pathways is expected)

Answer 1

Blood glucose regulation regulation

1. The liver functions as an important blood glucose buffer system. That is, when the blood glucose rises to a high concentration after a meal and the rate of insulin secretion also increases, as much as two thirds of the glucose absorbed from the gut is almost immediately stored in the liver in the form of glycogen.

Blood glucose control depends heavily on proteins called G-protein-coupled receptors (GPCRs). GPCRs span cell membranes to relay signals from the outside in. Once activated by the binding of a substance, GPCRs trigger a cascade of responses inside the cell. These receptors are thus important targets for drug development.

When blood glucose levels drop, such as after an overnight fast, the pancreas releases a hormone called glucagon. Glucagon binds a GPCR on liver and muscle cells called the glucagon receptor, which then stimulates the cells to release glucose into the bloodstream.

2. Both insulin and glucagon function as important feedback control systems for maintaining a normal blood glucose concentration. When the glucose con centration rises too high, increased insulin secretion causes the blood glucose concentration to decrease toward normal. Conversely, a decrease in blood glu cose stimulates glucagon secretion; the glucagon then functions in the opposite direction to increase the glu cose toward normal. Under most normal conditions, the insulin feedback mechanism is much more impor tant than the glucagon mechanism, but in instances of starvation or excessive utilization of glucose during exercise and other stressful situations, the glucagon mechanism also becomes valuable.

3. Also, in severe hypoglycemia, the prolyl endopeptidase enzyme — located in a part of the hypothalamus known as the ventromedial nucleus — sets a series of steps in motion that control glucose levels in the blood.

hypothalamus stimulates the sympathetic nervous system. The epinephrine secreted by the adrenal glands further increases release of glucose from the liver. This also helps protect against severe hypoglycemia.

4. And finally, over a period of hours and days, both growth hormone and cortisol are secreted in response to prolonged hypoglycemia. They both decrease the rate of glucose utilization by most cells of the body, converting instead to greater amounts of fat utilization. This, too, helps return the blood glucose concentration toward normal.