Answer
Body water is about 66%( 60-70%) of the human body by weight About of this water is extracellular water(ECF) most of which is in the blood-- which is about 84% water. The amount of water in blood is critical for maintaining blood volume and blood pressure. When blood volume decreases, blood pressure decreases, and homeostatic mechanisms are triggered to recover normal blood parameters volume , pressure, and flow.
Work Step by Step
Sweating and evaporation of sweat are body mechanisms for enhancing heat loss, and returning the body to normal temperature. Evaporation is an effective heat loss process, but it entails the loss of much extracellular water from the blood. Loss of water from plasma means that blood volume declines.A decline in blood volume results in a decrease in blood pressure. These changes are picked up by internal receptors; the stimuli travel by vagus sensory fibers to the solitary nucleus( of the medulla) which relays the stimulus to the preoptic area of the hypothalamus. The hypothalamus and thalamus have osmotic receptors and thirst centers (thalamus) and these have a roles in signaling thirst. Dry mouth, dehydration and the thalamus thirst center signals make us aware that we are thirsty and need to take in water. The signal to drink is a negative feedback signal because it depresses and eventually shuts off the original thirst or dehydration stimulus.
