Electrolyte gel is applied first, and then a weak current of frequency 50kHz is introduced. In the traditional BIA method, a person lies on a cot and spot electrodes are placed on the hands and bare feet. Intracellular fluid may then be estimated by subtracting extracellular fluid from total body water.īioelectrical impedance analysis Īnother method of determining total body water percentage (TBW%) is via bioelectrical impedance analysis (BIA). total body water: tritiated water or heavy water.The water in individual compartments can be measured with different substances: The total body water is then accurately measured from the increase in breath deuterium content in relation to the volume of D 2O ingested. Then, the FA-MS instrument measures the ratio D:H of deuterium to hydrogen in the water vapour in exhaled breath. A known dose of deuterated water ( heavy water, D 2O) is ingested and allowed to equilibrate within the body water. Measurement Dilution and equilibration Īn individual’s total body water can be determined using flowing-afterglow mass spectrometry (FA-MS) to measure the abundance of deuterium in breath samples. "third space," normally ignored in calculations) contained inside organs, such as the gastrointestinal, cerebrospinal, peritoneal, and ocular fluids. Interstitial fluid (4/5 of extracellular fluid).Of this 15 litres of extracellular fluid, plasma volume averages 3 litres, or 20%. For a 40-litre body, about 15 litres is extracellular, which amounts to 37.5%. Extracellular fluid (1/3 of body water) is fluid contained in areas outside of cells.Jackson's texts states 70% of body fluid is intracellular. In a 72 kg (159 lb) body containing 40 litres of fluid, about 25 litres is intracellular, which amounts to 62.5%. Intracellular fluid (2/3 of body water) is fluid contained within cells.In Netter's Atlas of Human Physiology (2002), body water is broken down into the following compartments: Adipose tissue contains about 10% of water, while muscle tissue contains about 75%. Water is also contained inside organs, in gastrointestinal, cerebrospinal, peritoneal, and ocular fluids. These include intracellular fluid extracellular fluid plasma interstitial fluid and transcellular fluid. Most animal body water is contained in various body fluids. So there is not, and cannot be, a figure that is exactly the same for all people, for this or any other physiological measure. These statistical averages will vary with factors such as type of population, age of people sampled, number of people sampled, and methodology. This is due to how fat tissue does not retain water as well as lean tissue. The body water constitutes as much as 75% of the body weight of a newborn infant, whereas some obese people are as little as 45% water by weight. ![]() The figure for water fraction by weight in this sample was found to be 58 ☘% water for males and 48 ☖% for females. However, this varied substantially by age, sex, and adiposity (amount of fat in body composition). ![]() In a large study of adults of all ages and both sexes, the adult human body averaged ~65% water. ![]() There can be considerable variation in body water percentage based on a number of factors like age, health, water intake, weight, and sex. Ensuring the right amount of body water is part of fluid balance, an aspect of homeostasis.īy weight, the average adult human is approximately 60% water, and the average child is approximately 70% water. This water makes up a significant fraction of the human body, both by weight and by volume. The percentages of body water contained in various fluid compartments add up to total body water (TBW). In physiology, body water is the water content of an animal body that is contained in the tissues, the blood, the bones and elsewhere.
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