Diabetes is a metabolic disorder, arising either due to (1) relative or absolute deficiency of a digestive hormone called insulin of (2) inability or resistance of body-cells to use the available insulin. The disorder completely throws the metabolism of dietary carbohydrates, fats and proteins into disarray.
To gain a clear understanding of the disease it is necessary to procure basic knowledge about the pancreas gland and the function of its secretion insulin in the body.
Pancreas is a digestive gland, which lies deep in the upper part of the abdomen, between the lower border of stomach and the upper border of duodenum. On either side, it is flanked by kidneys. The human pancreas weighs about 100 gms and is made up of small units called lobules. Each lobule consists of two groups of cells, the exocrine and the endocrine. Each endocrine group of cells is also called an islet of Langerhans. The beta cells of the islets produce insulin whereas the alpha cells of the islets produce a hormone glucogon, whose action is opposite to that of insulin.
The role of insulin
The carbohydrates in our food are digested in the intestines. The end-products of carbohydrate-digestion are various sugars, chiefly glucose. This glucose is absorbed through the mucous membrane of intestines to enter the blood-stream. Thus the concentration of glucose in the blood rises. Insulin makes this glucose available to each and every cell of the body. Each cell in our body is a tiny engine that uses glucose as fuel to generate heat and energy. If glucosefuel is to gain entrance into the cellular engine, insulin is essential.
If the amount of glucose in the blood is greater than the cellular requirements, insulin converts it into glycogen and fat which are stored in the liver (or muscles) and adipose tissue respectively.
Insulin is also concerned with the metabolism of dietary fats and proteins. The end-products of fat-digestion are fatty acids. Insulin converts these fatty acids back into fat and stores it in the adipose tissue. Again, insulin prevents the conversion of stored fat into fatty acids. Insulin is also essential for protein-synthesis in the body. If there is a deficiency of insulin, proteins lost due to wear and tear cannot be replaced.
Besides, insulin also serves certain other functions, the exact nature of which is not yet completely understood.
In short, the most important and obvious function of insulin is to control the concentration of glucose in the blood. After taking food, the concentration of glucose in blood rises. Insulin prevents the glucose concentration to rise above normal or physiological limits.
If insulin is inadequate or absent, the glucose in blood cannot enter various body-cells or cannot be converted into glycogen. Consequently, blood-glucose level rises.
When the blood passes through the kidneys, the glucose is normally not allowed to escape in the urine. However, when due to lack of insulin, the concentration of glucose increases beyond a particular level, it surpasses the efficiency level of kidneys (called renal threshold) and spills into the urine. That is the reason why the urine of diabetics is sweet.
Let us again consider cellular nutrition. Normally the nutritional requirements of body-cells are satisfied by glucose. When due to deficiency of insulin or due to resistance of cells to insulin, glucose cannot enter the cells, cellular starvation ensues. To supply nutrition to the starving cells, the body starts disintegrating stored fats and proteins. It is because of the destruction of muscle-protein and fats that a diabetic experiences undue weakness or fatigue and weight-loss respectively.
While defining diabetes, it was said that it is a condition arising due either to (1) deficiency of insulin or (2) inability of body-cells to use available insulin. The first type of diabetes is called Juvenile or insulin dependent diabetes mellitus (lDDM). It afflicts mostly children or young adults and produces acute symptoms. The second type of diabetes is called non-insulin-dependent or maturity onset diabetes mellitus (NIDDM). It mostly afflicts middle-aged persons and produces mild symptoms. In our country, almost 99 % of all diabetics suffer from the latter variety of diabetes.