The polyuria and polydypsia seen in patients with diabetes mellitus results from which of the following?

a. Inability to increase the amount of glucose reaching the kidneys the kidneys.

b. The inability to reabsorb all of the glucose filtered from the blood at the level of the kidneys

c. Decreased thirst receptor activity at the hypothalamus

B. The inability to reabsorb all of the glucose filtered from the blood at the level of the kidneys.

Explanation:

Diabetes mellitus is a syndrome caused by either lack of insulin or decreased sensitivity of insulin receptors. Type I diabetes is due to lack of insulin secretion where as type II diabetes is due to decreased sensitivity of target tissue to the insulin hormone.

Polyuria i. e excess urine secretion and polydypsia i. e increased flluid intake due to increased thirst are the classic symptoms of diabetes. When the glucose level in blood increases, its not completely reabsorbed from the renal tubules in the kidney, the excess glucose thus enters into the filtrate and moves out along with urine. This normally happens if the blood glucose is as high as 180 mg/100 ml or above. The loss of glucose in urine causes osmotic diuresis. Due to the osmotic effect of glucose in the renal tubules, the tubular reabsorption of water decreases thereby increasing the overall volume of urine. Both extracellular and intracellular dehydration are symptoms of diabetes mellitus.