Fluid and Electrolyte Balance
The regulation of the body’s water and of the dissolved salts (electrolytes — chiefly sodium, potassium, and chloride) within it. Together these set the volume and the concentration of every body fluid.
Two things are balanced
Section titled “Two things are balanced”- Volume — the total amount of body water, which influences blood pressure.
- Concentration (osmolarity) — how dilute or concentrated the fluids are, which must stay steady or cells will swell or shrink.
How it is regulated
Section titled “How it is regulated”- The kidneys are the main effector, fine-tuning how much water and salt are kept or excreted.
- Vasopressin (ADH) controls water reabsorption.
- Aldosterone, via the RAAS, controls sodium retention.
- Thirst, triggered by the hypothalamus, drives water intake.
Key idea
Section titled “Key idea”The body regulates water and salt together because each determines the other’s effect — it is balancing not just how much fluid there is, but how concentrated it is.