The desire to drink. Thirst is one means by which the amount of water in the body is controlled (the other is the volume of urine excreted).
Thirst is stimulated by an increased concentration of salt, sugar, or certain other substances in the blood. As the blood passes through the hypothalamus in the brain, special nerve receptors are stimulated, inducing the sensation of thirst. Thirst is also stimulated if blood volume decreases as a result of sweating, vomiting, diarrhoea, severe bleeding, or extensive burns. Thirst may also be caused by a dry mouth.
The sensation of thirst is generally felt at the back of the throat, because, when there is a de?ciency of water in the system, the throat and mouth especially become parched by evaporation of moisture from their surface. Thirst is increased by heat, and is a constant symptom of FEVER; it is also present in diseases which remove a considerable amount of ?uid from the system, such as diarrhoea, DIABETES MELLITUS and DIABETES INSIPIDUS, and after great loss of blood by haemorrhage. A demand for water is also a feature of many conditions associated with prolonged exertion, severe exhaustion and DEHYDRATION.
A strong and persistent need to drink, most commonly due to dehydration. Other causes include untreated diabetes mellitus and diabetes insipidus, kidney failure, treatment with phenothiazine drugs, and severe blood loss. Abnormal thirst may also be due to a psychological condition known as psychogenic polydipsia.... thirst, excessive
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