Body fluids composition, compartments and distribution

The body fluids They are all the liquids that are found in the different compartments of the human body and that fulfill multiple functions, both in the transport of nutrients and in the regulation of temperature and in the maintenance of cellular and corporal homeostasis.

More than 60% of the human body is made up of water, which is divided between two compartments known as the intracellular space and the extracellular space. This is also true for many animals and plants, hence water is such an essential liquid..

The intracellular space contains the intracellular fluid which, of all cells combined, represents about 40% of the body weight of the average adult human..

The extracellular space fluid corresponds to more or less 20% of body weight and is considered divided into interstitial fluid, blood plasma and some fluids contained in special compartments.

Article index

• 1 Intracellular and extracellular fluid
• 2 Composition of body fluids
  • 2.1 Intracellular fluid
  • 2.2 Interstitial fluid
  • 2.3 Blood plasma
  • 2.4 Composition of the extracellular fluids contained in some special compartments
• 3 Compartments and distribution of body fluids
• 4 References

Intracellular and extracellular fluid

Both intracellular fluid and extracellular fluids are of utmost importance for the proper functioning of the human body as a whole:

- All the fundamental catalytic reactions for metabolism, division and maintenance of internal cellular conditions take place in the intracellular fluid..

- Interstitial fluid is essential for the maintenance of cellular integrity, as well as for cellular communication and the regulation of many of the functions related to cells..

- Blood plasma corresponds to 60% of the fluid found in the vascular compartments and is an important vehicle for the transport of cells, nutrients and other factors throughout the body..

- Aqueous humor, cerebrospinal, pleural, pericardial and synovial fluids, as well as serous secretions and other glandular secretions are extracellular fluids contained in special compartments that perform different functions in the body, all with more or less equal importance..

Composition of body fluids

Intracellular fluid

The intracellular fluid is what is part of the cytosol. It is mainly composed of water, in which different types of ions are dissolved, a large amount of proteins (with or without enzymatic activity), sugars and other metabolites important for cells.

While proteins in the intracellular fluid represent about 30% of the total weight of a cell, the average concentrations of the ions in the intracellular fluid of human cells are as follows:

• Sodium (Na +): 10-30 mmol / L
• Potassium (K +): 130-150 mmol / L
• Magnesium (Mg2 +): 10-20 mmol / L
• Calcium (Ca2 +): less than 1 mmol / L
• Chlorine (Cl-): 10-20 mmol / L
• Phosphate ions (PO4-): 100-130 mmol / L
• Bicarbonate ion (HCO3-): less than 10 mmol / L
• Sulfate Ions (SO4-): about 20 mmol / L

Interstitial fluid

Interstitial fluid is that found in the interstitial extracellular space and is the one that contains and surrounds the cells of the body.

Like intracellular fluid, interstitial fluid is made up mainly of water, where different types of particles are also dissolved, electrolytes (anions and cations) being the most important. The concentration of these in said liquid is as follows:

• Sodium (Na +): 142 meq / L
• Potassium (K +): 4.1 meq / L
• Calcium (Ca ++): 2.4 meq / L
• Magnesium (Mg ++): 1 meq / L
• Chlorine (Cl-): 117 meq / L
• Bicarbonate (HCO3-): 27.1 meq / L
• Proteins: <0,1 meq/L
• Others: 8.4 meq / L

Blood plasma

Plasma is the extracellular fluid that is contained in the vascular compartments. Its composition is similar to that of interstitial fluid with respect to the identity of some of the particles dissolved in it, but not with respect to their concentration, which is as follows:

• Sodium (Na +): 153 meq / L
• Potassium (K +): 4.3 meq / L
• Calcium (Ca ++): 2.7 meq / L
• Magnesium (Mg ++): 1.1 meq / L
• Chlorine (Cl-): 112 meq / L
• Bicarbonate (HCO3-): 25.8 meq / L
• Proteins: 15.1 meq / L
• Others: 8.2 meq / L

Composition of the extracellular fluids contained in some special compartments

Vitreous humor

The vitreous humor is the liquid that occupies a large part of the volume of the eyeball. It is a transparent liquid that participates in some aspects of vision and the protection of the eye against trauma.

It is composed of more than 95% water, in which some minerals such as potassium, chlorine and sodium are dissolved. It also contains collagen fibers and other proteins along with hyaluronic acid.

Cerebrospinal fluid

This fluid is derived from blood plasma and is confined to the cavities of the central nervous system (brain and spinal cord). It participates in the protection of the brain and in the maintenance of pressure within the skull, as well as in many other processes involved in the health of the central nervous system..

Its composition is very similar to that of blood plasma, but it differs by having a lower abundance of proteins (almost 200 times less), and by having vitamins and some metabolites absent in plasma.

Synovial fluid

This fluid is the one that is enclosed inside the joint capsules of the synovial joints, so it is essential for the union and movement of different bones in the body..

It is composed of the same ions found in blood plasma, but it is described as an “ultrafiltrate” of it, with a high content of hyaluronic acid..

Compartments and distribution of body fluids

As we have already mentioned, body fluids are distributed throughout the body in two different compartments: the intracellular compartment and the extracellular compartment..

The intracellular compartment corresponds to the space contained inside the cells, that is, the one that is enclosed or delimited by the plasma membrane and that contains a substance known as cytosol.

The extracellular compartment is, as its name implies, the space comprised by the surroundings of cells. The fluid contained in the extracellular compartment is divided into three: interstitial fluid, blood plasma, and fluids contained in special compartments of the body..

Interstitial fluid surrounds cells, bathing and "supporting" them. Blood plasma travels through vascular compartments throughout the body and there are other body fluids, many derived from plasma, that are present at very specific sites:

• The eyeballs contain al vitreous humor.
• The spinal cord and brain, which represent the central nervous system, are in permanent contact with the cerebrospinal fluid.
• The pericardial fluid It is located in the layer of the heart known as the pericardium and is responsible for lubricating this organ.
• In the pleura, which is the tissue that covers the thoracic cavity, is the pleural fluid, fulfilling essential lubrication functions.
• There is also the synovial fluid, which is enclosed within the synovial joints, through which most of the bones of the axial skeleton (upper and lower extremities) are articulated.

References

1. Alberts, B., Bray, D., Hopkin, K., Johnson, A. D., Lewis, J., Raff, M.,… & Walter, P. (2013). Essential cell biology. Garland science
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