1a. Diabetes insipidus is a condition in which the patient suffers from insistent thirst, drinks a lot of water, and passes a great amount urine all day. This is usually caused by inadequate secretion/release of antidiuretic hormone (ADH) by the hypothalamus and posterior pituitary. This condition can also be the result of inability of the kidneys to respond to ADH.
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Excessive urine production is also a symptom of diabetes mellitus. In this case, however, the problem is not a defect in functioning of the hypothalamus-pituitary axis. In this disease the tissues are unable to utilize glucose efficiently. As a result, the blood of diabetics have abnormally high levels of glucose, some of which spills into the urine. High glucose levels in the urine is called glycosuria. The high osmolality of this urine is what pulls more water into the urinary tubules and results in more fluid (urine) entering the urethra to be voided as urine.