Lack of Effect of Insulin on Glucose Uptake and Usage by the Brain

Lack of Effect of Insulin on Glucose Uptake
and Usage by the Brain

The brain is quite different from most other tissues of the body in that insulin has little effect on uptake or
use of glucose. Instead, the brain cells are permeable to glucose and can use glucose without the intermediation of insulin.

The brain cells are also quite different from most other cells of the body in that they normally use only
glucose for energy and can use other energy substrates, such as fats, only with difficulty.
Therefore, it is essential that the blood glucose level always be maintained above a critical level, which is one of the most important functions of the blood glucose control system.
When the blood glucose falls too low, into
the range of 20 to 50 mg/100 ml, symptoms of hypoglycemic shock develop, characterized by progressive
nervous irritability that leads to fainting, seizures, and even coma.

Effect of Insulin on Carbohydrate Metabolism
in Other Cells
Insulin increases glucose transport into and glucose usage by most other cells of the body (with the exception of the brain cells, as noted) in the same way that it affects glucose transport and usage in muscle cells.
The transport of glucose into adipose cells mainly provides substrate for the glycerol portion of the fat molecule.
 Therefore, in this indirect way, insulin promotes deposition of fat in these cells.
 
 References:
© Copyright Guyton and Hall Textbook of Medical Physiology