Examine individual changes

'{{distinguish|Body of water}} In [[physiology]], '''body water''' is the [[water]] content of an [[animal body]] that is contained in the tissues, the blood, the bones and elsewhere. The percentages of body water contained in various [[compartment (pharmacokinetics)|fluid compartments]] add up to '''total body water''' (TBW). This water makes up a significant fraction of the [[human body]], both by weight and by volume. Ensuring the right amount of body water is part of [[fluid balance]], an aspect of [[homeostasis]]. ==Location== By weight, the average human adult male is approximately 70% water.<ref name="Jackson1979">{{cite book | title=Anatomy & Physiology for Nurses |last=Jackson| first=Sheila| year=1985| edition=9th| series=Nurses' Aids Series| publisher=Bailliere Tindall| location=London| isbn=0-7020-0737-4}}</ref> {{better source|date=October 2016}} <ref name="textbookofmedicalphysiology5thed">{{cite book |title=Textbook of Medical Physiology | last=Guyton |first=Arthur C. |year=1976| edition=5th| publisher=W.B. Saunders| location=Philadelphia| pages= 284, 424| isbn=0-7216-4393-0}}</ref> {{Failed verification|date=October 2016}} There can be considerable variation in body water percentage based on a number of factors like age, health, weight, and sex. In a large study of adults of all ages and both sexes, the adult human body averaged ~65% water. However, this varied substantially by age, sex, and adiposity (amount of fat in [[body composition]]). The figure for water fraction by weight in this sample was found to be 48 ±6% for females and 58 ±8% water for males.<ref>{{cite journal| title = Total body water volumes for adult males and females estimated from simple anthropometric measurements.|url = http://ajcn.nutrition.org/content/33/1/27.full.pdf| publisher = [[The American Journal of Clinical Nutrition]]|subscription = yes|volume = 33| date = January 1980| issue = 1 }}</ref> The body water constitutes as much as 73% of the body weight of a newborn infant, whereas some obese people are as little as 45% water by weight.<ref name="textbookofmedicalphysiology5thed" /> These figures statistical averages will vary with factors such as type of population, age of people sampled, number of people sampled, and methodology. So there is not, and cannot be, a figure that is exactly the same for all people, for this or any other physiological measure.<!--Anchor for redirect of [Animal body water] article; caution. --> Most of animal body water is contained in various [[body fluid]]s. These include [[intracellular fluid]]; [[extracellular fluid]]; [[Blood plasma|plasma]]; [[interstitial fluid]]; and [[transcellular fluid]].<ref name="John T. Hansen, Bruce M. Koeppen, 2002">{{cite book |author1=John T. Hansen |author2=Bruce M. Koeppen |title=Netter's Atlas of Human Physiology |publisher=Icon Learning Systems |location=Teterboro, N.J |year=2002 |isbn=1-929007-01-9}}</ref> Water is also contained inside organs, in [[Gastrointestinal physiology#Secretion|gastrointestinal]], [[cerebrospinal fluid|cerebrospinal]], [[peritoneal fluid|peritoneal]], and [[Aqueous humour|ocular]] fluids. [[Adipose tissue]] contains about 10% of water, while [[muscle tissue]] contains about 75%.<ref name=aniprod/><ref>{{cite web|url=https://books.google.com/books?id=FcA6zIq0d48C|title=Nutrient Requirements of Nonhuman Primates:|work=google.com}}</ref> In ''Netter's Atlas of Human Physiology'', body water is broken down into the following ''compartments:''<ref name="John T. Hansen, Bruce M. Koeppen, 2002"/> * [[Intracellular fluid]] (2/3 of body water) is fluid contained within cells. In a 72-kg body containing 40 litres of fluid, about 25 litres is intracellular,<ref name=guyton2>{{cite book |title=Textbook of Medical Physiology | last=Guyton |first=Arthur C. |year=1976| edition=5th| publisher=W.B. Saunders| location=Philadelphia| pages= 275| isbn=0-7216-4393-0}}</ref> which amounts to 62.5%. Jackson's texts states 70% of body fluid is intracellular.<ref name=Jackson1979 /> * [[Extracellular fluid]] (1/3 of body water) is fluid contained in areas outside of cells. For a 40-litre body, about 15 litres is extracellular,<ref name=guyton2/> which amounts to 37.5%. ** [[Blood plasma|Plasma]] (1/5 of extracellular fluid). Of this 15 litres of extracellular fluid, plasma volume averages 3 litres<ref name=guyton2/>, or 20%. ** [[Interstitial fluid]] (4/5 of extracellular fluid) ** [[Transcellular fluid]] (a.k.a. "third space," normally ignored in calculations) contained inside organs, such as the [[gastrointestinal]], [[cerebrospinal fluid|cerebrospinal]], peritoneal, and [[Human eye|ocular]] fluids. ==Measurement== ===Dilution and equilibration=== Total body water can be determined using [[Flowing afterglow mass spectrometry]] measurement of [[deuterium]] abundance in breath samples from individuals. A known dose of deuterated water ([[Heavy water]], D₂O) is ingested and allowed to equilibrate within the body water. The FA-MS instrument then measures the deuterium-to-hydrogen (D:H) ratio in the exhaled breath water vapour. The total body water is then accurately measured from the increase in breath deuterium content in relation to the volume of D₂O ingested. Different substances can be used to measure different fluid compartments:<ref>{{GeorgiaPhysiology|7/7ch02/7ch02p13}}</ref> * total body water: [[tritiated water]] or [[heavy water]]. * [[extracellular fluid]]: [[inulin]] * [[blood plasma]]: [[Evans blue]] [[Intracellular fluid]] may then be estimated by subtracting extracellular fluid from total body water. ===Bioelectrical impedance analysis=== Another method of determining total body water percentage (TBW%) is via [[Bioelectrical Impedance Analysis]] (BIA). In the traditional BIA method, a person lies on a cot and spot electrodes are placed on the hands and bare feet. Electrolyte gel is applied first, and then a weak current of frequency 50&nbsp;kHz is introduced. This AC waveform allows the creation of a current inside the body via the very capacitive skin without causing a DC flow or burns, and limited in the ~20mA range current for safety.<ref name="US Patent 4719922">{{cite web|url=http://www.patentstorm.us/patents/4719922/description.html|title=US Patent 4719922, Stimulator Apparatus - this website has ended|work=patentstorm.us}}</ref> BIA has emerged as a promising technique because of its simplicity, low cost, high reproducibility and noninvasiveness. BIA prediction equations can be either generalized or population-specific, allowing this method to be potentially very accurate. Selecting the appropriate equation is important to determining the quality of the results. For clinical purposes, scientists are developing a multi-frequency BIA method that may further improve the method's ability to predict a person's hydration level. New segmental BIA equipment that uses more electrodes may lead to more precise measurements of specific parts of the body. == Functions == Water in the animal body performs a number of functions: as a solvent for transportation of nutrients; as a medium for [[excretion]]; a means for heat control; as a lubricant for joints; and for shock absorption.<ref name="aniprod">{{cite web|url=https://books.google.com/books?id=0UPDQQOgr5YC&pg=PA47&lpg=PA47&dq=%22animal+body+water%22&source=bl&ots=lgiH5WdhyJ&sig=g3oAL6_TNDK2vyWL20J2r9SIAa4&hl=en&ei=81veTuPLIKqmiQLWpbjsCA&sa=X&oi=book_result&ct=result&resnum=10&ved=0CFwQ6AEwCQ#v=onepage&q=%22animal%20body%20water%22&f=false|title=FCS Animal Production L2|work=google.com}}</ref> ==Changes== The usual way of adding water to a body is by [[drinking]]. Water also enters the body with foods, especially those rich in water, such as plants, [[raw meat]], and fish. The amount of this water that is retained in animals is affected by several factors. Water amounts vary with the age of the animal. The older the [[vertebrate]] animal, the higher its relative bone mass and the lower its body water content. In diseased states, where body water is affected, the [[fluid compartments|fluid compartment or compartments]] that have changed can give clues to the nature of the problem, or problems. Body water is regulated by [[hormone]]s, including [[anti-diuretic hormone]], [[aldosterone]] and [[atrial natriuretic peptide]]. === Loss of water === {{Main|Volume contraction|Dehydration}} [[Volume contraction]] is a decrease in [[body fluid]] volume, with or without a concomitant loss of [[osmolyte]]s. The loss of the body water component of body fluid is specifically termed [[dehydration]].<ref>[http://www.medterms.com/script/main/art.asp?articlekey=2933 MedicineNet > Definition of Dehydration] Retrieved on July 2, 2009</ref> Sodium loss approximately correlates with fluid loss from [[extracellular fluid]], since sodium has a much higher concentration in extracelluliar fluid (ECF) than [[intracellular fluid]] (ICF). In contrast, K⁺ has a much higher concentration in ICF than ECF, and therefore its loss rather correlates with fluid loss from ICF, since K⁺ loss from ECF causes the K⁺ in ICF to diffuse out of the cells, dragging water with it by [[osmosis]].{{Citation needed|date=February 2016}} ==References== {{Reflist}} ==Further reading== *[https://books.google.com/books?id=en3Z1N8lF80C&pg=PT26 ''Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice''] *[https://books.google.com/books?id=M0XvP6mgmnkC&pg=PA180 ''Essentials of Animal Physiology''] *[https://books.google.com/books?id=JGBBhS-Wnz4C&pg=PA58 ''The Encyclopedia of Farm Animal Nutrition''] *[https://books.google.com/books?id=jlZg1VF-sKIC&pg=PA120 ''Animal Osmoregulation''] *[https://books.google.com/books?id=OG6qrtVKwTEC&pg=PA117 ''Animal Nutrition Science''] ==External links== {{portal|Animals}} * {{MeshName|Body+water}} * {{MeshName|Body+fluid+compartments}} {{Renal physiology}} [[Category:Body water| ]] [[Category:Humans]] [[de:Körperwasser]]'