Aldosterone is a steroid hormone with a molecular weight of 360.4. It is secreted by the glomerulosa zone of the adrenal gland and controls regulation of hydromineral metabolism. In the distal part of the nephron, aldosterone encourages reabsorption of Na and Cl- ions and secretion of K and H ions in blood vessel lumen. Thus there is an increase in extra-cellular osmolarity and water retention. Regulation of aldosterone secretion is linked to the body's water balance and brings three factors into play. These are the renin- angiotensin system, the plasmic Na /K ratio and, as a secondary factor, the ACTH. Physiologically, there seems to be circadian rythm for levels of aldosterone in the blood, which may be linked to changes in body posture. Aldosterone levels are higher for children than for adults, and increase during pregnancy.
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