The variation between individuals in the ratio of TBW to total body weight is quite large Location: The distinction between ICF and ECF is clear and is easy to. Extracellular fluid (ECF) or extracellular fluid volume (ECFV) usually denotes all body fluid outside the cells. The remainder is called intracellular fluid (ICF). Zero for the x-axis is on the line separating the ICF and the ECF. An increase in ECF volume expands the figure along the x-axis to the left, and an . An association between renal failure and bleeding tendency has long been recognized.
The lymphatic system returns protein and excess interstitial fluid to the circulation. The ionic composition of the interstitial fluid and blood plasma vary due to the Gibbs—Donnan effect. This causes a slight difference in the concentration of cations and anions between the two fluid compartments.
Cell membrane details between extracellular and intracellular fluid Sodium-potassium pump and the diffusion between extracellular fluid and intracellular fluid The extracellular fluid provides the medium for the exchange of substances between the ECF and the cells, and this can take place through dissolving, mixing and transporting in the fluid medium. These and many other substances occur, especially in association with various proteoglycans to form the extracellular matrix or the "filler" substance between the cells throughout the body.
Regulation[ edit ] The internal environment is stabilised in the process of homeostasis. Complex homeostatic mechanisms operate to regulate and keep the composition of the ECF stable. Individual cells can also regulate their internal composition by various mechanisms. There is a significant difference between the concentrations of sodium and potassium ions inside and outside the cell. The concentration of sodium ions is considerably higher in the extracellular fluid than in the intracellular fluid.
These differences cause all cell membranes to be electrically charged, with the positive charge on the outside of the cells and the negative charge on the inside. In a resting neuron not conducting an impulse the membrane potential is known as the resting potentialand between the two sides of the membrane is about mV.
The maintenance of this difference in the concentration of ions between the inside of the cell and the outside, is critical to keep normal cell volumes stable, and also to enable some cells to generate action potentials.
This allows a brief inflow of sodium ions into the cell driven in by the sodium ion concentration gradient that exists between the outside and inside of the cell. This causes the cell membrane to temporarily depolarize lose its electrical charge forming the basis of action potentials.
The sodium ions in the ECF also play an important role in the movement of water from one body compartment to the other. When tears are secreted, or saliva is formed, sodium ions are pumped from the ECF into the ducts in which these fluids are formed and collected. The water content of these solutions results from the fact water follows the sodium ions and accompanying anions osmotically. Calcium ions have a great propensity to bind to proteins. The proteins that are particularly sensitive to changes in the ECF ionized calcium concentration are several of the clotting factors in the blood plasma, which are functionless in the absence of calcium ions, but become fully functional on the addition of the correct concentration of calcium salts.
In addition, the pH of the ECF affects the proportion of the total amount of calcium in the plasma which occurs in the free, or ionized form, as opposed to the fraction that is bound to protein and phosphate ions.
Since the pH of the ECF is directly dependent on the partial pressure of carbon dioxide in the ECF, hyperventilationwhich lowers the partial pressure of carbon dioxide in the ECF, produces symptoms that are almost indistinguishable from low plasma ionized calcium concentrations. This means that nutrients can be secreted into the ECF in one place e. Hormones are similarly rapidly and evenly spread to every cell in the body, regardless of where they are secreted into the blood.
Oxygen taken up by the lungs from the alveolar air is also evenly distributed at the correct partial pressure to all the cells of the body. Waste products are also uniformly spread to the whole of the ECF, and are removed from this general circulation at specific points or organsonce again ensuring that there is generally no localized accumulation of unwanted compounds or excesses of otherwise essential substances e.
The only significant exception to this general principle is the plasma in the veinswhere the concentrations of dissolved substances in individual veins differs, to varying degrees, from those in the rest of the ECF. However this plasma is confined within the waterproof walls of the venous tubes, and therefore does not affect the interstitial fluid in which the body's cell live. Transcellular compartment[ edit ] The third extracellular compartment, the transcellular, consists of those spaces in the body where fluid does not normally collect in larger amounts,   or where any significant fluid collection is physiologically nonfunctional.
A small amount of fluid, called transcellular fluiddoes exist normally in such spaces.
Extracellular fluid - Wikipedia
For example, the aqueous humorthe vitreous humorthe cerebrospinal fluidthe serous fluid produced by the serous membranesand the synovial fluid produced by the synovial membranes are all transcellular fluids. They are all very important, yet there is not much of each. All of the aforementioned 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 ependymal cells, from blood plasma. Fluid shift[ edit ] Fluid shifts occur when the body's fluids move between the fluid compartments. Physiologically, this occurs by a combination of hydrostatic pressure gradients and osmotic pressure 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 vesselsblood pressure can drop to dangerously low levels, endangering critical organs such as the brainheart and kidneys ; when it shifts out of the cells the intracellular compartmentcellular processes slow down or cease from intracellular dehydration; when excessive fluid accumulates in the interstitial space, oedema develops; and fluid shifts into the brain cells can cause increased cranial pressure.
Fluid shifts may be compensated by fluid replacement or diuretics. Third spacing[ edit ] "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 burns or edemabut it can also refer to fluid shifts into a body cavity transcellular spacesuch as ascites and pleural effusions.
With regard to severe burns, fluids may pool on the burn site i. With pancreatitis or ileusfluids may "leak out" into the peritoneal cavityalso causing depletion of the intracellular, interstitial or vascular compartments. 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.