Hormones that circulate freely in the blood remain functional for less than one hour. Some hormones are functional for as little as two minutes. A hormone becomes inactivated when it diffuses out of the bloodstream and binds to receptors in target tissues or is absorbed and broken down by cells of the liver or kidneys. Enzymes in the plasma or interstitial fluids that break down hormones also cause them to become inactivated. Other hormones (e.g., renin) are activated by enzymes that cleave the active portion from a larger circulating precursor molecule.