How do humans keep a constant internal body temperature and water content?
Our body maintains internal homeostasis i.e. a constant internal environment of temperature, pH, water content etc. due to presence of hypothalamus.
Thermoregulatory center and the temperature sensors are located in the brain's hypothalamus.
The hypothalamus works by:
sensing through receptors,
receiving sensory messages from elsewhere,
sending messages through neurons and
controlling secretion of hormones.
Negative feedback mechanisms contribute to homeostatic control.
Water content of the body is controlled by the secretion of the posterior pituitary hormone vasopressin/anti diuretic hormone (ADH).
A decrease in water content in blood and tissue fluid will be sensed by hypothalamus. It has neurons which send axonic terminals to posterior pituitary capable of secreting hormone ADH. As these neurons respond by secreting more of the hormone, there will be more of absorption of water from filtrate along urinary tubules. Water content in blood will be soon normalised. This message will provide negative feedback to hypothalamus and secretion of ADH will slow down.