Thirst is stimulated: A. Before dehydration occurs. B. Once dehydration occurs. C. After blood volume decreases. D. After a decrease in plasma sodium concentration E. Both b and c are correct.

Thirst is stimulated once dehydration occurs and After blood volume decreases. The correct option is E.

Explanation: thirst is a mechanism physiological used by the body to maintain fluid balance. Once cellular dehydration occurs and decrease in blood volume is detected, thirst mechanism is stimulated to compensate the changes for proper body functioning. There are two types of thirst that the body can respond to, these are;

- Volumetric thirst: this is caused by decrease in blood volume ( that is hypovolemia). This can be fatal if not compensated by the body as it can lead to hypovolemic shock ( if the volume falls too low that the heart cannot circulate blood effectively. Cells in the kidney detects decreased blood volume and triggers thirst through the renin- angiotensin system

- osmometric thirst: this occurs when cellular dehydration is detected. This is when more water moves out of the individual cells than the amount of water taken in through drinking. These changes are detected by organum vasculosum of the lamina terminalis and subfornical organ to initiates water seeking and ingestive behavior.