Water Turnover
Start with the big picture
In adults, total body water is approximately 60% of body weight, divided mainly between intracellular and extracellular fluid. Daily turnover is about 2.5 L under steady-state conditions: water comes from drinks, food, and nutrient oxidation, and leaves chiefly through urine, insensible skin and lung losses, and feces. Plasma osmolality helps determine water distribution. Rising osmolality stimulates thirst and ADH, which increases collecting-duct water reabsorption; RAAS conserves sodium and water, while ANP promotes their renal loss. The topic also connects these controls to dehydration and overhydration, including changes in ADH and urine concentration. Fever, exertion, age, and the minimum urine volume needed for solute excretion are among the factors that shape water turnover.
What you'll learn
- Describe the main body-water compartments and their approximate proportions.
- Identify major daily sources of water intake and routes of output.
- Explain how thirst, ADH, RAAS, and ANP regulate water balance.
- Relate plasma osmolality and ADH responses to dehydration and overhydration.
- Recognize how fever, exertion, infancy, and aging affect water turnover.
Continue your study
Work through the complete notes and reinforce the topic with the study tools available in the full lesson.
