Dehydration
A lack of total body water disrupting metabolic processes.
Dehydration is a physiological condition characterized by a lack of total body water that disrupts metabolic processes. It occurs when free water loss exceeds intake, often resulting from excessive sweating, health conditions, or inadequate water consumption. The condition ranges from mild, which can impair cognitive performance, to severe, which can cause physical and mental deterioration and even death.
- field
- Physiology
- known_for
- Disruption of metabolic processes due to total body water loss
- risk_factors
- Exertion in heat, high altitudes, endurance athletics, elderly, infants, chronic illness
- mild_dehydration
- 1–2% body water loss impairs cognitive performance
- severe_dehydration
- Over 10% loss causes physical and mental deterioration; 15–25% loss can cause death
Lore & Background
Dehydration occurs when water intake does not replace free water lost through normal physiologic processes such as breathing, urination, and perspiration, or through causes like diarrhea and vomiting. The body's water content varies from 70–75% in newborns to less than 40% in obese adults, with an average of 60%. Water is classified as intracellular fluid (57% of total body water) and extracellular fluid (43%), which includes blood and interstitial fluid. When free water is lost, serum osmolarity increases, detected by osmoreceptors in the hypothalamus, triggering release of antidiuretic hormone (ADH) to increase water absorption in the kidneys and constrict blood vessels.
Reader's Guide
Dehydration is significant because it can lead to life-threatening conditions such as seizures or respiratory arrest, and carries the risk of osmotic cerebral edema if rehydration is overly rapid. It is distinct from hypovolemia, which specifically refers to a decrease in blood plasma volume; the two are regulated through independent mechanisms, making the distinction important in guiding treatment. Chronic dehydration can cause kidney stones and chronic kidney disease. In the elderly, blunted thirst response or inadequate access to water are main causes, and dehydration contributes to morbidity, especially in hot weather. Treatment for mild dehydration is oral rehydration; severe cases may need intravenous fluids.
Did You Know?
- Most people can tolerate a 3–4% decrease in total body water without difficulty.
- A 5–8% decrease in total body water can cause fatigue and dizziness.
- Death occurs with a 15 to 25% loss of body water.
- Dehydration can cause hypernatremia, which is distinct from hypovolemia.
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