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Blood – Special Tests

Regulation of sugar and diabetes
Concentration of blood sugar (glucose) remains steady up to 100 mg/dl during 24 hours. After partaking of food, it increases up to 140 – 150 mg/dl.
The ways by which glucose is added to the blood:

Absorption from the intestine.
By the breakdown of liver glycogen (glycogen is a starch like carbohydrate) to glucose.
By gluconeogenesis (a form of glucose from non–carbohydrates).

The ways by which glucose is removed from the blood:

By synthesis of fats e.g. triglycerides.
Conversion to liver glycogen.
Conversion to muscle glycogen.
In synthesis of glycoproteins and lactose etc.

When these processes are performed in the right balance, the blood sugar level remains within the normal limits of about 70 – 110 mg/dl. throughout the day. (Average 100 mg/dl).

The liver plays an important part by taking glucose from the blood and converting it into glycogen.
Releasing glucose from glycogen and converting pyruvate to glucose.
Muscle glycogen does not contribute directly to blood sugar. Glycogenolysis in the muscle produces locate, which is converted into glucose in the liver.
Kidney plays its part by the re–absorption of glucose when the blood glucose level is below 150 – 170 mg/dl (threshold level).

In normal individuals, the blood glucose level does not rise above the threshold level.
The following hormones play a part:
A. Insulin: It is secreted by the pancreas. It controls blood sugar in the following ways:

By increasing transport of glucose across the cell membrane.
By promoting oxidation of glucose or glycogen to pyruvate and lactate.
By increasing the formation of glucose from non–carbohydrates.
By decreasing conversion of glycogen to glucose.
By inhibiting conversion of protein to glucose and favoring a synthesis of protein from amino acids.
By promoting the transfer of potassium phosphate and amino acids into the cells.

Glucose is also regulated by other hormones than insulin but to a lesser extent. These hormones antagonize the action of insulin. They are:
B. Thyroxine (secreted by the thyroid gland).
C. Glucagon (secreted by alpha cells of the pancreas).
D. Growth hormone (secreted by the pituitary gland).
E. Glucocorticoids (secreted by the adrenal cortex).
F. Epinephrine (secreted by the adrenal medulla).
These hormones increase blood sugar levels by:

By increasing absorption of glucose from the intestine.
Decreasing the oxidation of glucose or glycogen to pyruvate and lactate.
Preventing synthesis of glycogen.
Stimulating synthesis of glycogen from glucose.
Stimulating the formation of glucose from non–carbohydrates.

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