- Aldosterone
Aldosterone is a hormone - one of the many molecules made by the body that signals elaborate actions on living tissues attuned to receive it. Those tissues with receptors for aldosterone include .
When aldosterone binds to these cells, new sodium channels are constructed, and existing ones are activated, and sodium is transported into the cells. Giving extra aldosterone to people seems to have the same effect as putting them on a no-salt diet long enough to deprive body stores of sodium, availasble sodium, in both situations, is moved into tissues.
Throughout the body, there is a pattern to the movement and management of two major single-positive charged mineral ions: sodium (chemical symbol:Na) and potassium (chemical symbol:K). Where Na+ goes, K+ tends to leave, and vice versa. And so, with inflows of sodium, facilitated by aldosterone, there are often balancing outflows of potassium.
In general, it is within the cells of the body that K+ exists in great plentitude, and it is outside those cells, in the extra-cellular fluid, and the plasma flowing in the blood vessels, that Na+ is predominant. The salt soutions on both sides of the cell's boundries, the inside of the cytoplasm and the outside of the extracellular fluid, have about the same charge and osmotic pressure. That term "osmotic pressure" refers, in a sense, to the drawlng power of the fluid. For example, when something is put in a fluid of higher osmotic pressure, it tends to get wrinkly and depleted of fluid - like the skin of your little finger stuck in salt brine. When gets put in a fluid of lower osmotic pressure, it tends to plump out with fluid, and its contents get diluted - like a raisin soaked in water. The something in these cases is permeable to water, water can move- to at least some extent, into and out of it.
In keeping with aldosterone's role of moving sodium into the cells, its actions towards potassium are opposite- to discard it.
- Chapter 21 - Disorders of Potassium Balance in Brenner: Brenner & Rector's The Kidney
