intracellular fluid

Examples of intracellular fluid in the following topics:

• Body Fluid Composition

  • The cytosol or intracellular fluid consists mostly of water, dissolved ions , small molecules, and large water-soluble molecules (such as proteins).
  • The pH of the intracellular fluid is 7.4.
  • The concentrations of the other ions in cytosol or intracellular fluid are quite different from those in extracellular fluid.
  • Ocular fluid in the eyes contrasts cerebrospinal fluid by containing high concentrations of proteins, including antibodies.
  • Describe the composition of intracellular and extracellular fluid in the body

• Fluid Compartments

  • The major body fluid compartments include: intracellular fluid and extracellular fluid (plasma, interstitial fluid, and trancellular fluid).
  • The intracellular fluid of the cytosol or intracellular fluid (or cytoplasm) is the fluid found inside cells.
  • Although water forms the large majority of the cytosol, its mainly functions as a fluid medium for intracellular signaling (signal transduction) within the cell, and plays a role in determining cell size and shape.
  • It is the intravascular fluid part of extracellular fluid (all body fluid outside of cells).
  • Examples of this fluid are cerebrospinal fluid, and ocular fluid, joint fluid, and the pleaural cavity which contain fluid that is only found in their respective epithelium-lined spaces.

• Water Content in the Body

  • A significant percentage of the human body is water, which includes intracellular and extracellular fluids.
  • Water also provides a fluid environment for extracellular communication and molecular transport throughout the body.
  • The water in the body is distributed among various fluid compartments that are interspersed in the various cavities of the body through different tissue types.
  • In diseased states where body water is affected, the fluid compartments that have changed can give clues to the nature of the problem.

• Anion Regulation

  • Adjustments in respiratory and renal functions allow the body to regulate the levels of these ions in the extracellular fluid (ECF).
  • Chloride is the predominant extracellular anion and is a major contributor to the osmotic pressure gradient between the intracellular fluid (ICF) and extracellular fluid (ECF).
  • Chloride also plays an important role in maintaining proper hydration and functions to balance cations in the ECF, maintaining the electrical neutrality of this fluid.
  • Only a small amount of CO2 can be dissolved in body fluids; thus, over 90 percent of the CO2 is converted into bicarbonate ions, HCO3–, through the following reactions:

• Resting Membrane Potentials

  • Most of the time, the difference in ionic composition of the intracellular and extracellular fluids and difference in ion permeability generates the resting membrane potential difference.

• Short-Term Chemical Control

  • When stimulated a signal transduction cascade leads to increased intracellular calcium from the sarcoplasmic reticulum through IP3 mediated calcium release, as well as enhanced calcium entry across the sarcolemma through calcium channels.
  • The rise in intracellular calcium complexes with calmodulin, which in turn activates myosin light chain kinase.
  • Once elevated, the intracellular calcium concentration is returned to its basal level through a variety of protein pumps and calcium exchangers located on the plasma membrane and sarcoplasmic reticulum.
  • Localized tissues utilize multiple ways to increase blood flow including releasing vasodilators, primarily adenosine, into the local interstitial fluid which diffuses to capillary beds provoking local vasodilation.
  • Dephosphorylation by myosin light-chain phosphatase and induction of calcium symportersand antiporters that pump calcium ions out of the intracellular compartment both contribute to smooth muscle cell relaxation and therefore vasodilation.

• Polycystic Kidney Disease

  • The cysts are numerous and are fluid-filled, resulting in massive enlargement of the kidneys.
  • Gene PKD-1 is located on chromosome 16, and codes for a protein involved in regulation of cell cycle and intracellular calcium transport in epithelial cells; it is responsible for 85% of the cases of ADPKD.
  • As the cysts accumulate fluid, they enlarge, separate entirely from the nephron, compress the neighboring renal parenchyma, and progressively compromise renal function.
  • Under the function of gene defect, epithelial cells of renal tubule turn into epithelial cells of cyst wall after phenotype change and begin to have the function of secreting cyst fluid, which leads to continuous cysts enlargement.

• Peripheral Motor Endings

  • Upon the arrival of an action potential at the presynaptic neuron terminal, voltage-dependent calcium channels open and Ca2+ ions flow from the extracellular fluid into the presynaptic neuron's cytosol.
  • As intracellular calcium levels rise, the motor proteins responsible for the contractile response are able to interact, as shown in Figure 3, to form cross-bridges and undergo shortening.
  • The binding of acetylcholine at the motor end plate leads to intracellular calcium release and interactions between myofibrils to elicit contraction.

• Extrauterine Effects of Estrogens and Progesterone

  • Progesterone exerts its primary action through the intracellular progesterone receptor although a distinct, membrane-bound progesterone receptor has also been postulated.
  • Also, elevated levels of progesterone potently reduce the sodium-retaining activity of aldosterone, resulting in natriuresis and a reduction in extracellular fluid volume.
  • Progesterone withdrawal, on the other hand, is associated with a temporary increase in sodium retention (reduced natriuresis, with an increase in extracellular fluid volume) due to the compensatory increase in aldosterone production.
  • Detailed characterization of the events occurring in sperm, in response to progesterone, has shed light on certain events including intracellular calcium transients and maintained changes, and slow calcium oscillations, now thought to possibly regulate motility.

• Chemical Buffer Systems

  • Extracellular buffers include bicarbonate and ammonia, whereas proteins and phosphate act as intracellular buffers.
  • In response to acidosis, tubular cells reabsorb more bicarbonate from the tubular fluid, collecting duct cells secrete more hydrogen and generate more bicarbonate, and ammoniagenesis leads to increased formation of the NH3 buffer.