Theory 41/Biology & physiology/Thirst
Thirst Balances Salt and Volume
The claim
Thirst is triggered when the ratio of plasma osmolality to blood volume exceeds a threshold, so the same water deficit produces thirst or none depending on salt load.
01Mechanism
Osmoreceptors and volume receptors both feed the drive; the ratio sets the integrated signal.
02Prediction
Thirst should track the ratio.
03Refutation
Thirst tracking volume alone would remove osmolality.