Antidiuretic hormone water loss regulated

Age-dependent differences have been observed in hormonal regulation of electrolytes. For example, antidiuretic hormones enhance water excretion in young rats, but inhibit it in old ones. Hydrocortisone has similar effects, increasing water and sodium output in young rats but reducing water loss in old animals. Aldosterone increases potassium retention in old rats but essentially has no effect in very young rats (110),... 

Fig. 4.10. Body fluid homeostasis (constant body water balance). Intake is influenced by availability of fluids and food, thirst, hunger, and the ability to swallow. The rates of breathing and evaporation and urinary volume influence water loss. The body adjusts the volume of urinary excretion to compensate for variations in other types of water loss and for variations in intake. The hormones aldosterone and antidiuretic hormone (ADH) help to monitor blood volume and osmolality through mechanisms regulating thirst and sodium and water balance.

Extracellular fluid balance is maintained through closely regulated loss and retention to ensure that the total level of fluid in the body remains constant. Mechanisms are in place for regulation of water loss, such as secretion of antidiuretic hormone (ADH) to stimulation retention of water in urine, which helps to prevent excessive fluid elimination. The mechanism of thirst (also stimulated by ADH, as well as by blood pressure) is used to stimulate the ingestion of fluids and fluid-containing foods. 3... 

There are two components to the regulation of ECE sodium the total amount of sodium retained and its concentration. The former is regulated by mechanisms that directly affect sodium, whereas the latter is essentially regulated via water balance. Thus, whatever sodium is retained in ECF is clothed with the appropriate amount of water to maintain the normal plasma sodium concentration within narrow limits deviations of less than 1% (hard to measure in the laboratory) trigger corrective responses. Thus, a raised plasma sodium concentration (e.g., after water loss) stimulates both thirst and renal water conservation antidiuretic hormone (ADH) from the posterior pituitary reduces urine output through its effect on the renal collecting ducts. Even one of these mechanisms can defend body water thus diabetes insipidus (inadequate production or effect of ADH) does not cause severe dehydration but polydipsia (increased fluid intake thirst is a sensation). 

---