1)Describe the detailed mechanism by which the hormonal changes associated with
ID: 63819 • Letter: 1
Question
1)Describe the detailed mechanism by which the hormonal changes associated with diabetes insipidus would trigger increased thirst.
How is diabetes insipidus usually treated? What complications may arise from unchecked diabetes insipidus?
2) In a fluid deprivation test, water is withheld from the patient and the osmolarity of urine is checked. How would urine osmolarity change in a healthy person in response to fluid deprivation? How would it change in someone with diabetes insipidus due to head trauma?
Explanation / Answer
1. Diabetes insipidus occurs when the body has a lower than normal amount of antidiuretic hormone (ADH). ADH is also called vasopressin. ADH is produced in a part of the brain called the hypothalamus. It is then stored and released from the pituitary gland. ADH controls the amount of water excreted in urine. Without ADH, the kidneys do not work properly to keep enough water in the body. The result is a rapid loss of water from the body in the form of dilute urine. This results in the need to drink large amounts of water due to extreme thirst and to make up for excessive water loss in the urine.
Diabetes insipidus (DI) occurs when the kidney tubules do not respond to a hormone in the body called antidiuretic hormone (ADH), also called vasopressin. ADH normally tells the kidneys to make the urine more concentrated. As a result of the defect, the kidneys release too much water into the urine. This causes the body to produce a large quantity of very dilute urine.
Vasopressin (desmopressin, DDAVP) is given either as a nasal spray, tablets, or injections. This controls urine output and fluid balance and prevents dehydration. In mild cases, drinking more water may be all that is needed. If the body's thirst control is not working (for example, if the hypothalamus is damaged), a prescription for a certain amount of water intake may also be needed to ensure proper hydration.
If the diabetes inspidus is unchecked it may lead to confusion and changes in alertness due to dehydration and higher than normal sodium level in the body, if the person is unable to drink.
2. The water deprivation test (i.e, the Miller-Moses test), a semiquantitative test to ensure adequate dehydration and maximal stimulation of ADH for diagnosis, is typically performed in patients with more chronic forms of DI. In healthy individuals, water deprivation leads to a urinary osmolality that is 2-4 times greater than plasma osmolality. In central and nephrogenic DI, urinary osmolality will be less than 300 mOsm/kg after water deprivation. After the administration of ADH, the osmolality will rise to more than 750 mOsm/kg in central DI but will not rise at all in nephrogenic DI.
The body's normal response to dehydration is to conserve water by concentrating the urine. Those with DI continue to urinate large amounts of dilute urine in spite of water deprivation.
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