Thirst is a perception associated with the body’s need for water. The body’s internal environment, the organs and tissues, requires certain amounts of water and mineral salts to function properly. Too much or too little water or salt can damage or destroy cells. Therefore, people and animals must control the balance of water and salt within their bodies. This balance is maintained mainly through the kidneys, which remove water and salts as urine, and the behaviors associated with seeking out and consuming water and other liquids.
People often describe thirst as a dry feeling in the throat. A lack of sufficient saliva can produce this kind of thirst, even when the internal environment has no need for water. In a similar way, the thirst sensation created by the internal environment’s need will disappear briefly if water is drunk and wets the throat. But unless the water reaches the internal environment, thirst will recur after a short time.
Sensory nerves in the internal organs and receptors (sensors) in the brain are affected by the volume of fluid both inside and outside of the body’s cells. These internal sensors detect the amount of water and salt present in different parts of the body (see Senses). The information is conveyed to the brain through chemical and nerve signals. Such information affects a region of the brain stem called the hypothalamus. The hypothalamus is important in maintaining the internal environment. Nerve activity in portions of the hypothalamus and other parts of the brain is associated with motivation to seek out and consume water. This motivational state is referred to as thirst.
