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Fluid compartments
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<h2 id="intracellular-compartment">Intracellular compartment</h2> <p>The intracellular fluid (ICF) is all fluids contained inside the cells, which consists of <a href="/facts/Cytosol/VyXgygWm">cytosol</a> and fluid in the <a href="/facts/Cell_nucleus/D7sFRa3c">cell nucleus</a>.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> The cytosol is the matrix in which cellular <a href="/facts/Organelle/vhDFnGbs">organelles</a> are suspended. The cytosol and organelles together compose the <a href="/facts/Cytoplasm/Wa0sE6xf">cytoplasm</a>. The <a href="/facts/Cell_membrane/vAXSD0DT">cell membranes</a> are the outer barrier. In humans, the intracellular compartment contains on average about 28 liters (6.2 imp gal; 7.4 U.S. gal) of fluid, and under ordinary circumstances remains in <a href="/facts/Osmosis/vYPfyX76">osmotic</a> equilibrium. It contains moderate quantities of magnesium and sulfate ions. </p><p>In the cell nucleus, the fluid component of the <a href="/facts/Nucleoplasm/PNGpzgCK">nucleoplasm</a> is called the nucleosol.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> </p> <h2 id="extracellular-compartment">Extracellular compartment</h2> <p>The interstitial, intravascular and transcellular compartments comprise the extracellular compartment. Its <a href="/facts/Extracellular_fluid/hzm4qatP">extracellular fluid</a> (ECF) contains about one-third of <a href="/facts/Total_body_water/eJwKlDTD">total body water</a>. </p> <h3>Intravascular compartment</h3> <p>The main intravascular fluid in mammals is <a href="/facts/Blood/03zEulkj">blood</a>, a complex <a href="/facts/Mixture/tms8rbmn">mixture</a> with elements of a <a href="/facts/Suspension_(chemistry)/S3xp96TL">suspension</a> (<a href="/facts/Blood_cell/lf9GA0Dj">blood cells</a>), <a href="/facts/Colloid/9EVucqND">colloid</a> (<a href="/facts/Globulin/cMDP5CGc">globulins</a>), and <a href="/facts/Solutes/MGchhMQV">solutes</a> (<a href="/facts/Glucose/oUSkoLCD">glucose</a> and <a href="/facts/Ion/3bePpDna">ions</a>). The blood represents both the intracellular compartment (the fluid inside the blood cells) and the extracellular compartment (the <a href="/facts/Blood_plasma/oHuwwugG">blood plasma</a>). The average volume of plasma in the average (70-kilogram or 150-pound) male is approximately 3.5 liters (0.77 imp gal; 0.92 U.S. gal). The volume of the intravascular compartment is regulated in part by <a href="/facts/Fluid_statics/GYu6ljQ0">hydrostatic</a> pressure gradients, and by reabsorption by the kidneys. </p> <h3>Interstitial compartment</h3> <p>The interstitial compartment (also called "tissue space") surrounds tissue cells. It is filled with <a href="/facts/Interstitial_fluid/hzm4qatP">interstitial fluid</a>, including lymph.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> Interstitial fluid provides the immediate <a href="/facts/Microenvironment_(biology)/hJuxlEHS">microenvironment</a> that allows for movement of <a href="/facts/Ions/wrbwhF3z">ions</a>, <a href="/facts/Proteins/Jxmagu3E">proteins</a> and <a href="/facts/Nutrients/34bn4skK">nutrients</a> across the cell barrier. This fluid is not static, but is continually being refreshed by the <a href="/facts/Capillary/4BIzKJAe">blood capillaries</a> and recollected by <a href="/facts/Lymph_capillary/eYeHIbeI">lymphatic capillaries</a>. In the average male (70-kilogram or 150-pound) human body, the interstitial space has approximately 10.5 liters (2.3 imp gal; 2.8 U.S. gal) of fluid. </p> <h3>Transcellular compartment</h3> <p>The transcellular fluid is the portion of total body fluid that is formed by the secretory activity of epithelial cells and is contained within specialized epithelial-lined compartments. Fluid does not normally collect in larger amounts in these spaces,<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a><a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> and any significant fluid collection in these spaces is physiologically nonfunctional.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> Examples of transcellular spaces include the eye, the central nervous system, the <a href="/facts/Peritoneal_cavity/rSFbPzn1">peritoneal</a> and <a href="/facts/Pleural_cavity/Wel4Tz7p">pleural</a> cavities, and the <a href="/facts/Joint_capsule/WaDLdl8h">joint capsules</a>. A small amount of fluid, called <a href="/facts/Transcellular_fluid/hzm4qatP">transcellular fluid</a>, does exist normally in such spaces. For example, the <a href="/facts/Aqueous_humor/EywsjoQo">aqueous humor</a>, the <a href="/facts/Vitreous_humor/jBNl5YV5">vitreous humor</a>, the <a href="/facts/Cerebrospinal_fluid/tcWG7hhv">cerebrospinal fluid</a>, the <a href="/facts/Serous_fluid/LLgNVbvp">serous fluid</a> produced by the <a href="/facts/Serous_membrane/vj8eDs43">serous membranes</a>, and the <a href="/facts/Synovial_fluid/KbM378Sg">synovial fluid</a> produced by the <a href="/facts/Synovial_membrane/kWEY5l7V">synovial membranes</a> are all transcellular fluids. They are all very important, yet there is not much of each. For example, there is only about 150 milliliters (5.3 imp fl oz; 5.1 U.S. fl oz) of cerebrospinal fluid in the entire central nervous system at any moment. All of the above-mentioned fluids are produced by active cellular processes working with blood plasma as the raw material, and they are all more or less similar to blood plasma except for certain modifications tailored to their function. For example, the cerebrospinal fluid is made by various cells of the CNS, mostly the <a href="/facts/Ependyma/eyHxnkyt">ependymal</a> cells, from blood plasma. </p> <h2 id="fluid-shift">Fluid shift</h2> <p><i>Fluid shifts</i> occur when the body's fluids move between the fluid compartments. Physiologically, this occurs by a combination of <a href="/facts/Hydrostatic_pressure/GYu6ljQ0">hydrostatic pressure</a> gradients and <a href="/facts/Osmotic_pressure/6oWKTsXV">osmotic pressure</a> gradients. Water will move from one space into the next passively across a semi permeable membrane until the hydrostatic and osmotic pressure gradients balance each other. Many medical conditions can cause fluid shifts. When fluid moves out of the intravascular compartment (the blood vessels), blood pressure can drop to dangerously low levels, endangering critical organs such as the <a href="/facts/Brain/EKla9NkJ">brain</a>, <a href="/facts/Heart/fF4KSGdk">heart</a> and <a href="/facts/Kidney/HBspPrv9">kidneys</a>; when it shifts out of the cells (the intracellular compartment), cellular processes slow down or cease from intracellular dehydration; when excessive fluid accumulates in the interstitial space, <a href="/facts/Oedema/Q6MI3KdH">oedema</a> develops; and fluid shifts into the brain cells can cause increased cranial pressure. Fluid shifts may be compensated by <a href="/facts/Fluid_replacement/hQ1mMS6W">fluid replacement</a> or <a href="/facts/Diuretic/x3j4I1Tg">diuretics</a>. </p> <h3>Third spacing</h3> <p>"Third spacing" is the abnormal accumulation of fluid into an extracellular and extravascular space. In medicine, the term is often used with regard to loss of fluid into interstitial spaces, such as with <a href="/facts/Burn_(injury)/EHdVoSxB">burns</a> or <a href="/facts/Edema/Q6MI3KdH">edema</a>, but it can also refer to fluid shifts into a body cavity (transcellular space), such as <a href="/facts/Ascites/sftkD7MA">ascites</a> and <a href="/facts/Pleural_effusion/34Y7pyFv">pleural effusions</a>. With regard to severe burns, fluids may pool on the burn site (i.e. fluid lying outside of the interstitial tissue, exposed to evaporation) and cause depletion of the fluids. With <a href="/facts/Pancreatitis/gmbNTcCG">pancreatitis</a> or <a href="/facts/Ileus/1rMI0juo">ileus</a>, fluids may "leak out" into the <a href="/facts/Peritoneal_cavity/rSFbPzn1">peritoneal cavity</a>, also causing depletion of the intracellular, interstitial or vascular compartments. </p><p>Patients who undergo long, difficult operations in large surgical fields can collect third-space fluids and become intravascularly depleted despite large volumes of intravenous fluid and blood replacement. </p><p>The precise volume of fluid in a patient's third spaces changes over time and is difficult to accurately quantify. </p><p>Third spacing conditions may include <a href="/facts/Peritonitis/pWjYb4MB">peritonitis</a>, <a href="/facts/Pyometritis/RAdFcJty">pyometritis</a>, and <a href="/facts/Pleural_effusion/34Y7pyFv">pleural effusions</a>.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> <a href="/facts/Hydrocephalus/HF9jQqTq">Hydrocephalus</a> and <a href="/facts/Glaucoma/MWqWVNz3">glaucoma</a> are theoretically forms of third spacing, but the volumes are too small to induce significant shifts in blood volumes, or overall body volumes, and thus are generally not referred to as third spacing. </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Blood%E2%80%93brain_barrier/xYzvVwdu">Blood–brain barrier</a></li> <li><a href="/facts/Compartment_(pharmacokinetics)/I8B9eaze">Compartment (pharmacokinetics)</a></li> <li><a href="/facts/Distribution_(pharmacology)/f8Hkox6Q">Distribution (pharmacology)</a> and volume of distribution</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Rodney A. Rhoades; David R. Bell (18 January 2012). Medical Physiology: Principles for Clinical Medicine. Lippincott Williams & Wilkins. pp. 5–6. ISBN 978-1-60913-427-3. <a href="978-1-60913-427-3" target="_blank">978-1-60913-427-3</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Jacob M, Chappell D, Rehm M (2009). "The 'third space'--fact or fiction?". Best Pract Res Clin Anaesthesiol. 23 (2): 145–57. doi:10.1016/j.bpa.2009.05.001. PMID 19653435. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Liachovitzky, Carlos (2015). "Human Anatomy and Physiology Preparatory Course" (pdf). Open Educational Resources. CUNY Academic Works: 69. Archived from the original on 2017-08-23. Retrieved 2021-06-22. <a href="https://academicworks.cuny.edu/bx_oers/1/" target="_blank">https://academicworks.cuny.edu/bx_oers/1/</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Usage example: Schweiger, A; Mazur, G (1974-09-15) [1974]. "Mammalian proteins with affinity to polynucleotides: Isolation by affinity chromatography from rat liver cytosol and nucleosol". FEBS Letters. 46 (1–2). p255, right column, line 11. doi:10.1016/0014-5793(74)80381-9. PMID 4417675. A soluble fraction of rat liver nuclei (nucleosol) was... <a href="https://doi.org/10.1016%2F0014-5793%2874%2980381-9" target="_blank">https://doi.org/10.1016%2F0014-5793%2874%2980381-9</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>"Fluid Physiology: 2.1 Fluid Compartments". <a href="http://www.anaesthesiamcq.com/FluidBook/fl2_1.php" target="_blank">http://www.anaesthesiamcq.com/FluidBook/fl2_1.php</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Barbara Kuhn Timby (1 January 2008). Fundamental Nursing Skills and Concepts. Lippincott Williams & Wilkins. pp. 319–. ISBN 978-0-7817-7909-8. Retrieved 9 June 2010. <a href="978-0-7817-7909-8" target="_blank">978-0-7817-7909-8</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Redden M, Wotton K (June 2002). "Third-space fluid shift in elderly patients undergoing gastrointestinal surgery: Part 1: Pathophysiological mechanisms". Contemp Nurse. 12 (3): 275–83. doi:10.5172/conu.12.3.275. PMID 12219956. S2CID 19554202. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Drain, Cecil B. (2003). Perianesthesia nursing: a critical care approach. Philadelphia: W.B. Saunders Co. ISBN 0-7216-9257-5. [1] <a href="0-7216-9257-5" target="_blank">0-7216-9257-5</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>"FLUID AND ELECTROLYTE THERAPY". Archived from the original on 2010-07-07. Retrieved 2010-06-08. <a href="https://web.archive.org/web/20100707084536/http://www.cvmbs.colostate.edu/clinsci/wing/fluids/fluids.htm" target="_blank">https://web.archive.org/web/20100707084536/http://www.cvmbs.colostate.edu/clinsci/wing/fluids/fluids.htm</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> </ol>