Insulin Promotes Liver Uptake, Storage, and
Use of Glucose
One of the most important of all the effects of insulin is to cause most of the glucose absorbed after a meal to be stored almost immediately in the liver in the form of glycogen. Then, between meals, when food is not available and the blood glucose concentration begins to fall, insulin secretion decreases rapidly and the liver glycogen is split back into glucose, which is released back into the blood to keep the glucose concentration from falling too low.
The mechanism by which insulin causes glucose uptake and storage in the liver includes several almost simultaneous steps:
1. Insulin inactivates liver phosphorylase,the principal enzyme that causes liver glycogen to split into glucose.
2. Insulin causes enhanced uptake of glucose from the blood by the liver cells.
3. Insulin also increases the activities of the enzymes that promote glycogen synthesis, including especially glycogen synthase, which is responsible for polymerization of the monosaccharide units to form the glycogen molecules.