The body watches blood volume like a thermostat. When volume or BP drops too low, it turns on hormones that retain salt and water. Those are RAAS and ADH. When volume runs too high, the stretched heart releases hormones that dump salt and water. Those are ANP and BNP. Flip the volume and watch who responds.
The volume thermostat
The kidney and the heart with their hormone signals. Active pathways glow and quiet ones fade.
Set the volume state to begin.
① Set blood volume / BP
② Pick a hormone to learn
What it does
Simple rule:low volume → RAAS and ADH turn ON to retain. Aldosterone keeps salt & water, and ADH keeps water. High volume → the stretched heart fires ANP/BNP to dump salt & water. RAAS and ADH are the opposite of ANP and BNP.