Chapter 38.2, Problem 1CSC

Insulin is a large, water-soluble hormone that binds to receptors on the outside surface of muscle, fat, and several other cell types. Insulin binding to its receptors activates proteins that in turn stimulate or inhibit many enzymes inside the cell. One of the activated enzymes starts a cascade of reactions inside the cell, with the result that glucose-transporting proteins are moved to the plasma membrane. Once in the plasma membrane, the transport proteins facilitate the diffusion of glucose into the cell.

Insulin is essential to regulate metabolism and sustain life, but it can have a dark side, too. Excessive insulin, particularly if combined with fasting, can stimulate muscle and fat cells to take up too much glucose from the blood. In extreme cases, blood glucose can drop so low that a person goes into insulin shock. Deprived of glucose, the brain shuts down, and the victim may faint, go into a coma, and die. There have even been a couple of cases of “murder by insulin.” But insulin shock never happens in a properly functioning human body. Why not? How does the body regulate insulin release and glucose metabolism preventing insulin shock? Or regulate the release of other hormones, so you don’t grow so tall that you can't stand up, or become so frightened by a loud noise that your heart fails?