Effect of Insulin on Carbohydrate Metabolism

Immediately after a high-carbohydrate meal, the glucose that is absorbed into the blood causes rapid
secretion of insulin, which is discussed in detail later in the chapter.The insulin in turn causes rapid uptake,
storage, and use of glucose by almost all tissues of the body, but especially by the muscles, adipose tissue, and liver.

Insulin Promotes Muscle Glucose Uptake
and Metabolism

During much of the day, muscle tissue depends not on glucose for its energy but on fatty acids. The principal
reason for this is that the normal resting muscle membrane is only slightly permeable to glucose, except
when the muscle fiber is stimulated by insulin; between meals, the amount of insulin that is secreted is too
small to promote significant amounts of glucose entry into the muscle cells.

However, under two conditions the muscles do use large amounts of glucose. One of these is during moderate or heavy exercise.This usage of glucose does not require large amounts of insulin, because exercising muscle fibers become more permeable to glucose even in the absence of insulin because of the contraction process itself.

The second condition for muscle usage of large amounts of glucose is during the few hours after a
meal. At this time the blood glucose concentration is high and the pancreas is secreting large quantities of
insulin. The extra insulin causes rapid transport of glucose into the muscle cells. This causes the muscle
cell during this period to use glucose preferentially over fatty acids, as we discuss later.

Storage of Glycogen in Muscle.

If the muscles are not exercising after a meal and yet glucose is transported into the muscle cells in abundance, then most of the glucose is stored in the form of muscle glycogen instead of being used for energy, up to a limit of 2 to 3 per cent concentration. The glycogen can later be used for energy by the muscle. It is especially useful for short periods of extreme energy use by the muscles and even to provide spurts of anaerobic energy for a few minutes at a time by glycolytic breakdown of the glycogen to lactic acid, which can occur even in the absence of oxygen.

 References:
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