natriuresis

Natriuresis simply means flushing sodium out in the urine. The word combines “natrium” (sodium) with “-uresis” (urinating), so it literally describes the kidney letting salt go. It is the body’s main way to get rid of excess salt and, with it, excess water.

Because sodium holds water in the circulation, dumping sodium also sheds fluid, which lowers blood volume and pressure. The kidney increases natriuresis when the body is salt- and volume-loaded, and natriuretic peptides released by the stretched heart actively command it. These peptides push sodium out, oppose the salt-retaining renin-angiotensin-aldosterone system, and so act as a brake on rising volume and pressure.

Natriuresis is also how many blood-pressure medicines work. Diuretics force the kidney to excrete more sodium and water, deliberately producing natriuresis to lower volume and pressure. A related idea, “pressure natriuresis,” describes how a rise in blood pressure itself nudges the kidney to excrete more salt, providing a built-in long-term defense against high pressure.