This lesson explains how the body balances daily water intake and loss, how the brain detects dehydration, and how several responses encourage water conservation and drinking.
Water is essential to the body's tissues and normal functions. On a typical day, an adult takes in about 2,500 mL of aqueous fluids, mostly through the digestive tract. Metabolism contributes approximately 230 mL of water each day during the final stages of aerobic respiration.
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What is osmolality?
Osmolality is the concentration of solutes relative to the amount of solvent in a solution. Plasma osmolality compares solutes with water in blood plasma.
What is insensible water loss?
It is water loss that a person is usually unaware of, especially evaporation from the skin and water lost in exhaled air.
How do hypothalamic osmoreceptors contribute to thirst?
They detect increased plasma osmolality and signal the hypothalamus, which produces conscious thirst and encourages drinking.
How do aldosterone and sodium affect water balance?
Aldosterone increases sodium reabsorption in the kidney's distal tubules. Water follows the reabsorbed sodium back into the blood.
Why can dehydration be especially dangerous for infants?
Because infants have low body mass, they can become dangerously dehydrated very quickly when water losses are not replaced.
Quiz questions
Approximately how much water is produced each day as a by-product of metabolism?Answer: About 230 mL.
After a person drinks a large quantity of fluid, when does diuresis generally begin?Answer: About 30 minutes later.
What minimum urine volume per day is needed to support normal waste removal?Answer: About 0.47 liters.
How does alcohol increase urine output, according to its effect on water balance?Answer: It inhibits ADH release, reducing water reabsorption by the kidneys.
What effect can ADH have on arterioles in the peripheral circulation?Answer: It constricts them, helping increase blood supply to the body's core.
Based on Anatomy and Physiology 2e by J. Gordon Betts, Kelly A. Young, James A. Wise, Eddie Johnson, Brandon Poe, Dean H. Kruse, Oksana Korol, Jody E. Johnson, Mark Womble, Peter DeSaix (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.