What is the distribution of fluids in various compartments?
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There are three major fluid compartments; intravascular, interstitial, and intracellular. Fluid movement from the intravascular to interstitial and intracellular compartments occurs in the capillaries. A capillary “membrane,” which consists of the endothelial glycocalyx, endothelial cells, and the subendothelial cell matrix, separates the capillary intravascular space from the interstitial fluid compartment. This capillary “membrane” is freely permeable to water and small-molecular-weight particles such as electrolytes, glucose, acetate, lactate, gluconate, and bicarbonate. Gases such as oxygen and carbon dioxide diffuse freely through this membrane, following their concentration gradient, to enter or exit the intravascular compartment. Show
The interstitial compartment is the space between the capillaries and the cells. Fluids support the matrix and cells within the interstitial space. The intracellular compartment is separated from the interstitial space by a cell membrane. This membrane is freely permeable to water but not to small- or large-molecular-weight particles. Any particle movement between the interstitium and the cell must occur through some transport mechanism (eg, channel, ion pump, carrier mechanism). Fluids are in a constant state of flux across the capillary endothelial membrane, through the interstitium, and into and out of the cell. The amount of fluid that moves across the capillary “membrane” depends on a number of factors, including capillary colloid oncotic pressure (COP), hydrostatic pressure, and permeability, which is dictated by factors such as the endothelial glycocalyx layer (EGL) and pore sizes between the cells. The natural particles in blood that create COP are proteins: primarily albumin but also globulins, fibrinogen, and others. The hydrostatic pressure within the capillary is the pressure forcing outward on the capillary membrane generated by the blood pressure and cardiac output. Fluid moves into the interstitial space when intravascular hydrostatic pressure is increased over COP, when membrane pore size increases, the EGL is disrupted, or when intravascular COP becomes lower than interstitial COP. The EGL is now known to play an important role in controlling fluid and other molecule (eg, albumin) transport across the capillary layer, and the oncotic pressure of the glycocalyx plays a larger role than the oncotic pressure of the interstitium; various disease processes and therapy (such as IV fluid administration) can significantly disrupt the EGL, resulting in altered transcapillary movement. \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\) The major body-fluid compartments includ: intracellular fluid and extracellular fluid (plasma, interstitial fluid, and transcellular fluid). Learning Objectives
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Fluid CompartmentsThe fluids of the various tissues of the human body are divided into fluid compartments. Fluid compartments are generally used to compare the position and characteristics of fluid in relation to the fluid within other compartments. While fluid compartments may share some characteristics with the divisions defined by the anatomical compartments of the body, these terms are not one in the same. Fluid compartments are defined by their position relative to the cellular membrane of the cells that make up the body’s tissues. Intracellular FluidThe intracellular fluid of the cytosol or intracellular fluid (or cytoplasm ) is the fluid found inside cells. It is separated into compartments by membranes that encircle the various organelles of the cell. For example, the mitochondrial matrix separates the mitochondrion into compartments. The contents of a eukaryotic cell within the cell membrane, excluding the cell nucleus and other membrane-bound organelles (e.g., mitochondria, plastides, lumen of endoplasmic reticulum, etc.), is referred to as the cytoplasm.  The cytosol: The cytosol (11) is the fluid within the plasma membrane of a cell and contains the organelles. The cytosol includes dissolved molecules and water. The cytosol is a complex mixture of substances dissolved in water. Although water forms the large majority of the cytosol, it mainly functions as a fluid medium for intracellular signaling (signal transduction ) within the cell, and plays a role in determining cell size and shape. The concentrations of ions, such as sodium and potassium, are generally lower in the cytosol compared to the extracellular fluid; these differences in ion levels are important in processes such as osmoregulation and signal transduction. The cytosol also contains large amounts of macromolecules that can alter how molecules behave, through macromolecular crowding. Extracellular FluidExtracellular fluid (ECF) or extracellular fluid volume (ECFV) usually denotes all the body fluid that is outside of the cells. The extracellular fluid can be divided into two major subcompartments: interstitial fluid and blood plasma. The extracellular fluid also includes the transcellular fluid; this makes up only about 2.5% of the ECF. In humans, the normal glucose concentration of extracellular fluid that is regulated by homeostasis is approximately 5 mm. The pH of extracellular fluid is tightly regulated by buffers and maintained around 7.4. The volume of ECF is typically 15L (of which 12L is interstitial fluid and 3L is plasma). The ECF contains extracellular matrices (ECMs) that act as fluids of suspension for cells and molecules inside the ECF. Extracellular matrix: Spatial relationship between the blood vessels, basement membranes, and interstitial space between structures. Blood PlasmaBlood plasma is the straw-colored/pale-yellow, liquid component of blood that normally holds the blood cells in whole blood in suspension, making it a type of ECM for blood cells and a diverse group of molecules. It makes up about 55% of total blood volume. It is the intravascular fluid part of the extracellular fluid. It is mostly water (93% by volume) and contains dissolved proteins (the major proteins are fibrinogens, globulins, and albumins), glucose, clotting factors, mineral ions (Na+, Ca++, Mg++, HCO3- Cl-, etc.), hormones, and carbon dioxide (plasma is the main medium for excretory product transportation). It plays a vital role in intravascular osmotic effects that keep electrolyte levels balanced and protects the body from infection and other blood disorders. Interstitial FluidInterstitial fluid (or tissue fluid) is a solution that bathes and surrounds the cells of multicellular animals. The interstitial fluid is found in the interstitial spaces, also known as the tissue spaces. On average, a person has about 11 liters (2.4 imperial gallons or about 2.9 U.S. gal) of interstitial fluid that provide the cells of the body with nutrients and a means of waste removal. The majority of the interstitial space functions as an ECM, a fluid space consisting of cell-excreted molecules that lies between the basement membranes of the interstitial spaces. The interstitial ECM contains a great deal of connective tissue and proteins (such as collagen) that are involved in blood clotting and wound healing. Transcellular FluidTranscellular fluid is the portion of total body water contained within the epithelial-lined spaces. It is the smallest component of extracellular fluid, which also includes interstitial fluid and plasma. It is often not calculated as a fraction of the extracellular fluid, but it is about 2.5% of the total body water. Examples of this fluid are cerebrospinal fluid, ocular fluid, joint fluid, and the pleaural cavity that contains fluid that is only found in their respective epithelium-lined spaces. The function of transcellular fluid is mainly lubrication of these cavities, and sometimes electrolyte transport. 25.2B: Fluid Compartments is shared under a CC BY-SA license and was authored, remixed, and/or curated by LibreTexts. How body fluids are distributed in compartments?Fluid is separated into compartments by semipermeable membranes. The membranes are highly permeable to water but require energy to transport ions. Distribution of fluid between intracellular and extracellular compartments is determined by the concentration of Na+, chloride. Electrolytes (Cl–), and other electrolytes.
What are the distribution of body fluids?The distribution of fluid throughout the body can be broken down into two general categories: intracellular fluid and extracellular fluid. Intracellular fluid is approximately 40% of the total body weight. It is the total space within cells primarily defined as the cytoplasm of cells.
What are the 3 main fluid compartments in the body?In the human body plan, there are three major fluid compartments that are functionally interconnected. These are the (1) intracellular fluid compartment, (2) interstitial fluid, and (3) plasma. Fluid, molecules, and ions flow across physical barriers between the fluid compartments.
What determines the distribution of fluid between intracellular and extracellular compartments?The distribution of fluid between intracellular and extracellular compartments, in contrast, is determined mainly by the osmotic effect of the smaller solutes— especially sodium, chloride, and other electrolytes— acting across the cell membrane.
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