Thirst

Image:William-Adolphe Bouguereau (1825-1905) - Thirst (1886).jpg Thirst is the basic need or instinct of humans or animals to drink. It arises from a lack of fluids and/or an increase in the concentration of certain osmolites such as salt. If the water volume of the body falls below a certain threshold, or the osmolite concentration becomes too high, the brain signals thirst. The osmolite concentration in the blood is measured with specialized sensors in the hypothalamus, notably in two circumventricular organs that lack an effective blood-brain barrier, the organum vasculosum of the lamina terminalis and the subfornical organ. These areas project to the supraoptic nucleus and paraventricular nucleus, which contain neurons that secrete the antidiuretic hormone, vasopressin, from their nerve endings in the posterior pituitary, but also project to other hypothalamic areas, including especially the median preoptic nucleus to trigger thirst. Continuous dehydration can cause myriad problems, but is most often associated with neurological problems such as seizures, and renal problems.

Excessive thirst, known as polydipsia, along with excessive urination, known as polyuria, may be an indication of diabetes.

Angiotensin II is a hormone which is a powerful dipsogen (ie it stimulates thirst) which acts via the subfornical organ.

[edit] Quotes

According to the Gospel of John, `I am thirsty` were some of Jesus`s very last words before his death. (19:28)

M.J. McKinley and A.K. Johnson (2004). "The Physiological Regulation of Thirst and Fluid Intake". News in Physiological Sciences 19 (1): 1-6. Retrieved on 2006-06-02.