Diabetes Mellitus Symptoms

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The classical diabetes mellitus symptoms are excessive urination (polyuria), excessive thirst (polydipsia), and excessive appetite (polyphagia). These symptoms are due to the high glucose level and inability of cells of make use of glucose as a source of energy.

Excessive urination (osmotic diuresis)

The symptom of excessive urination experienced by patients with diabetes is due to a process called osmotic diuresis. The high sugar level in the blood also increases the sugar level in the tubules of the kidneys. This elevated sugar level in the tubules attracts water. This is the same principle operating in the traditional experiment on osmosis: water moving across a semi-permeable membrane from the side with high water concentration (or low salt concentration) to the side with the low water concentration (or high salt concentration).

In the kidneys of a diabetic with high blood sugar, the space inside the kidney tubules has low water concentration (or high glucose concentration), and the space outside the tubules has a high water concentration (low glucose concentration), and the wall of the tubules acts as the semi-permeable membrane. In this scenario, water will move from outside the tubules (high water, low sugar) to inside (low water, high sugar). As the water inside the tubules will become part of the urine, this movement of water increases urine formation and produces the symptom of excessive urination.

Excessive thirst

This diabetes mellitus symptom is a result of excessive urination. A sustained increase in the amount of urine causes a reduction of total body water. This reduction is sensed by the central nervous system. The nervous system reacts by initiating the sensation of thirst. Unlike the usual thirst sensation which disappears after a drink of water, the thirst sensation in diabetics is sustained because the water loss in the urine is continuous. The cycle of excessive urination and thirst only stops when the glucose level is reduced.

Excessive appetite

Excessive appetite, or excessive eating without gaining weight, is a result of the inability of the cells of the body to make use of glucose in the blood as a source of energy.

In a non-diabetic, the rise of blood sugar level after a meal is accompanied by the release of insulin from the pancreas. Insulin promotes the entry of glucose inside the cell (see carbohydrate metabolism). In a diabetic, the elevation of glucose level after a meal is not accompanied by the release of insulin. The absence of insulin impairs the entry of glucose in the cell. This cellular starvation is detected by the central nervous system which brings about the hunger sensation. This sensation, like that of thirst, can not be satisfied until the underlying cause is corrected. It disappears only when the insulin level in the blood is increased.

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