mineralocorticoid

Mineralocorticoids are the branch of adrenal steroids in charge of the body's minerals and fluids — specifically sodium, potassium, and the water that follows them. The name says it: mineral-cortex-steroid. If glucocorticoids manage your energy, mineralocorticoids manage your plumbing, deciding how much salt to keep and how much to flush, which in turn sets your blood volume and blood pressure.

The dominant mineralocorticoid is aldosterone, made in the outermost cortical zone (the zona glomerulosa). Acting mainly on the kidney's distal tubules and collecting ducts, it tells the kidney to reabsorb sodium back into the blood and to excrete potassium into the urine. Because water tends to follow sodium, retaining salt also retains water, expanding fluid volume.

Their regulation is distinct from cortisol's. Aldosterone is controlled chiefly by the renin-angiotensin-aldosterone system, which responds to low blood pressure or low sodium, and directly by high blood potassium. Too much mineralocorticoid activity raises blood pressure and drops potassium; too little (as in Addison's disease) causes salt loss, dehydration, low blood pressure, and dangerously high potassium.