Blood : Special Tests

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.

Glucose travels throughout body and when it comes in contact with beta cells of pancreas, they secrete insulin in response to increased levels of glucose in the blood. This insulin attaches itself to each cell surface to make glucose molecules enter the cells to be used for energy. The cells require very little energy and the rest is stored as adenosine triphosphate (ATP). This is then used by the body. Everything in excess is stored by the muscles, the liver etc.

In case of a normal person, the fasting blood sugar level is 70 - 110 mg/dl. It does not fall below 70mg/dl due to the antagonizing effect of other hormones mentioned above. When the blood sugar rises to a relatively high level, the kidney filters it through glomeruli (network of tiny blood vessels) but it returns to the blood by the re-absorption system of its tubules.

Diabetes Mellitus

Diabetes Mellitus occurs when blood glucose is too high due to very less insulin or none at all. Sometimes, the pancreas produces normal amounts of insulin but the body needs more than the normal. As a result of this, the body suffers from a lack of energy. People with diabetes often complain of weakness and tiredness.

Characteristics of diabetes mellitus

	Raised fasting blood sugar levels.
	The amount of urine passed is increased often up to 5 to 6 liters of pale urine.
	Thirst.
	Due to lack of insulin glucose is not utilized by cells. Energy is obtained through:

Body proteins.

Fats.

This causes muscular weakness and results in weight loss. Also, the end product of protein is urea which increases above the normal range and causes discomfort.

	In severe cases, more fat is used for energy. The excessive oxidation of fatty acids increases ketone bodies in the blood and there is also an increase in cholesterol synthesis.
	In severe cases, the plasma bicarbonate decreases which results in a fall of blood pH and leads to a loss of sodium ions.

The last two conditions may result in diabetic coma.

Types of Diabetes.

There are two major types of diabetes. Type I and Type II

Type I Diabetes

It is insulin dependent diabetes mellitus (IDDM) or "juvenile diabetes." This occurs when beta cells of the pancreas do not function to produce insulin. Patients take supplementary insulin by injections because if taken orally it will get digested, as insulin is a protein in nature.

Insulin is either obtained from the pancreas of cattle or pigs, or produced synthetically, using recombinant DNA (deoxyribonucleic acid). This synthetic insulin does not stimulate the formation of antibodies against insulin as the animal insulin may do.

Most often young people get this type of diabetes and the onset is fast. Sometimes, older people also get Type I diabetes which has a slow onset and acts like Type II for a long period.

Type II Diabetes

This is non-insulin dependent diabetes mellitus (NIDDM). The body produces some insulin but the requirement is more. It may be due to reduction in the number of insulin producing beta cells. Due to this, glucose is unable to enter the cells as interaction between insulin and its receptor is less effective. People with this type of diabetes are usually above their ideal weight. Overeating also contributes to it, so diet is primary treatment for this type of diabetes. Generally people above the age of 40 get this type of diabetes, but it may be found in younger people also. About 85 per cent of all people who have diabetes, have Type II diabetes.

Other Types of Diabetes

Some people are not diabetic but may have an increased risk of developing diabetes.

Pre-diabetes

A person both of whose parents are diabetic, or who has an identical twin who develops diabetes, although he/she may not have diabetes initially is considered a prospect for the disease.

Latent diabetes

Some people have elevated blood glucose levels only in certain times of stress e.g. in pregnancy or during severe infection. They suffer from diabetes but become normal when pregnancy ends or after they recover from the infection.

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