thirst

Thirst is the conscious desire to drink fluids. It serves to regulate body water balance and maintain blood volume and electrolyte concentration. While often prompted by a dry mouth, true thirst stems from signaling pathways that monitor hydration status and plasma osmolality.

Physiology and regulation involve specialized sensors in the brain. Osmoreceptors in the hypothalamus detect increased blood osmolality, signaling the need to conserve water and to drink. A drop in blood volume or blood pressure activates the renin-angiotensin system, contributing to thirst. Antidiuretic hormone (vasopressin) is released to promote water reabsorption in the kidneys, helping restore balance. The sensation of thirst can be categorized as osmotic thirst (driven by osmolality) or hypovolemic thirst (driven by blood volume loss).

Triggers and manifestations vary. Dehydration from sweating, fever, diarrhea, or inadequate fluid intake raises thirst. High salt intake, dry mouth, diabetes, or certain medications can also promote thirst. In clinical contexts, excessive thirst is called polydipsia, which may accompany conditions such as diabetes mellitus or diabetes insipidus, while reduced thirst can be a risk factor for dehydration, especially in older adults.

Clinical relevance and management focus on maintaining fluid balance. Assessment considers intake and output, medical history, and signs of dehydration. Treatment emphasizes appropriate fluid intake and addressing underlying causes, with caution to avoid overhydration and electrolyte disturbances.