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Aldosterone is the primary of several endogenous members of the class of mineralocorticoids in humans. Deoxycorticosterone is another important member of this class. Aldosterone tends to promote Na+ and water retention, and lower plasma K+ concentration by the following mechanisms:
1. Acting on the nuclear mineralocorticoid receptors (MR) within the principal cells of the distal tubule and the collecting duct of the kidney nephron, it upregulates and activates the basolateralNa+/K+ pumps, which pumps three sodium ions out of the cell and two potassium ions into the cell. This results in reabsorption of sodium (Na+) ions and water (which follows sodium) into the blood, and secreting potassium (K+) ions into the urine (lumen of collecting duct).
2. Aldosterone upregulates epithelial sodium channels (ENaCs), increasing apical membrane permeability for Na+.
3. Cl− is reabsorbed in conjunction with sodium cations to maintain the system's electrochemical balance.
4. Aldosterone stimulates the secretion of K+ into the tubular lumen.
5. Aldosterone stimulates Na+ and water reabsorption from the gut, salivary and sweat glands in exchange for K+.
6. Aldosterone stimulates secretion of H+ in exchange for Na+ in the intercalated cells of the cortical collecting tubules, regulating plasma bicarbonate (HCO3−) levels and its acid/base balance.
Aldosterone is responsible for the reabsorption of about2% of filtered sodium in the kidneys, which is nearly equal to the entire sodium content in human blood under normal glomerular filtration rates.
Aldosterone, probably acting through mineralocorticoid receptors, may positively influence neurogenesis in the dentate gyrus.
Aldosterone is secreted in response to low salt levels. Aldosterone then activates the MR (for mineralocorticoid receptor) gene. (Aldosterone is classified as a mineralocorticoid hormone.) The product of the MR gene, in turn, stimulates the kidney to reabsorb and retain salt, thereby retaining water.
steroid hormone secreted by the adrenal gland and it keeps water and salt balance in the body, helping in maintaining the blood pressure
