Fluid compartments

Source: Wikipedia, the free encyclopedia.
(Redirected from
Third spacing
)

The

solutes, and suspended elements are segregated. The two main fluid compartments are the intracellular and extracellular compartments. The intracellular compartment is the space within the organism's cells; it is separated from the extracellular compartment by cell membranes.[1]

About two-thirds of the

fluids in the "transcellular compartment".

The normal processes by which life self-regulates its biochemistry (homeostasis) produce fluid balance across the fluid compartments. Water and electrolytes are continuously moving across barriers (eg, cell membranes, vessel walls), albeit often in small amounts, to maintain this healthy balance. The movement of these molecules is controlled and restricted by various mechanisms. When illnesses upset the balance, electrolyte imbalances can result.

The interstitial and intravascular compartments readily exchange water and solutes, but the third extracellular compartment, the transcellular, is thought of as separate from the other two and not in dynamic equilibrium with them.[2]

The science of fluid balance across fluid compartments has practical application in intravenous therapy, where doctors and nurses must predict fluid shifts and decide which IV fluids to give (for example, isotonic versus hypotonic), how much to give, and how fast (volume or mass per minute or hour).

Intracellular compartment

The intracellular fluid (ICF) is all fluids contained inside the cells, which consists of cytosol and fluid in the cell nucleus.[3] The cytosol is the matrix in which cellular organelles are suspended. The cytosol and organelles together compose the cytoplasm. The cell membranes 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 osmotic equilibrium. It contains moderate quantities of magnesium and sulfate ions.

In the cell nucleus, the fluid component of the nucleoplasm is called the nucleosol.[4]

Extracellular compartment

The interstitial, intravascular and transcellular compartments comprise the extracellular compartment. Its

total body water
.

Intravascular compartment

The main intravascular fluid in mammals is

hydrostatic
pressure gradients, and by reabsorption by the kidneys.

Interstitial compartment

The interstitial compartment (also called "tissue space") surrounds tissue cells. It is filled with

nutrients across the cell barrier. This fluid is not static, but is continually being refreshed by the blood capillaries and recollected by lymphatic capillaries
. 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.

Transcellular compartment

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,

vitreous humor, the cerebrospinal fluid, the serous fluid produced by the serous membranes, and the synovial fluid produced by the synovial membranes 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 ependymal
cells, from blood plasma.

Fluid shift

Fluid shifts occur when the body's fluids move between the fluid compartments. Physiologically, this occurs by a combination of

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

"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 edema, but it can also refer to fluid shifts into a body cavity (transcellular space), such as ascites and pleural effusions. 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 pancreatitis or ileus, fluids may "leak out" into the peritoneal cavity
, also 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.

The precise volume of fluid in a patient's third spaces changes over time and is difficult to accurately quantify.

Third spacing conditions may include

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.

See also

References

  1. .
  2. .
  3. ^ 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.
  4. PMID 4417675
    . A soluble fraction of rat liver nuclei (nucleosol) was...
  5. ^ "Fluid Physiology: 2.1 Fluid Compartments".
  6. . Retrieved 9 June 2010.
  7. .
  8. ^ "FLUID AND ELECTROLYTE THERAPY". Archived from the original on 2010-07-07. Retrieved 2010-06-08.