Interstitial space and interstitial fluid: fluid and intercellular space

2021-05-29 01:41 PM

About one-sixth of the total volume of the body is the space between cells, which is called the interstitial space. The fluids in these spaces are called interstitial fluid.

The main function of microcirculation is to transport nutrients to tissues and remove cellular waste products. Small arterioles control blood flow to individual tissues and their local condition, by controlling the diameter of the arterioles. Thus, in most cases, each tissue's regulation of flow is related to its own needs.

The walls of the capillaries are very thin and are composed of a layer of highly permeable endothelial cells. Thus, water, cellular nutrients and cellular secretion products can be exchanged quickly and easily between tissues and circulating blood.

The human body's peripheral circulatory system has about 10 billion capillaries with an estimated total surface area of ​​500 to 700 square meters (about one-eighth of the surface area of ​​a football field). Thus, any functioning cell has a capillary that feeds it no more than 20-30 micrometres away.

About one-sixth of the total volume of the body is the space between cells, which is called the interstitial space. The fluids in these spaces are called interstitial fluid.

The structure of the interstitial space is shown in Fig.

Figure. The structure of the interstitial space. Proteoglycan fibres are everywhere in the space between collagen fibrils. Free vesicles and small amounts of fluid from the channels are sometimes present

It consists of two main types of solid structures: (1) collagen fibre bundles and (2) proteoglycan fibres. The collagen fibre bundles have a length spread in the interstitial. They are very strong and thus generate most of the tension of the tissues. However, proteoglycan polysaccharide filaments are extremely thin coiled or helical molecules containing about 98 percent uronichyal-acid and 2 percent protein. These molecules are so thin that they cannot be seen with a light microscope and are difficult to characterize even with an electron microscope. They do, however, form a carpet of very strong mesh fibres described as a "brush frill".

Interstitial glue

Fluid in the interstitial space is formed by filtration and diffusion from the capillaries.

It contains almost the same components as plasma except the protein concentration is much lower because the protein does not easily pass outside through the capillary pores.

Interstitial fluid is produced mainly in the small spaces between the proteoglycan fibres. The binding of the interstitial fluid and the proteoglycan inside gives it the characteristics of a gel and is therefore called gel tissue.

Because there are so many proteoglycan fibres, it is really difficult for the fluid to circulate easily through the gel tissues. Instead, the fluid is mainly diffused through the gel; that is, it moves through the molecule from one place to another using kinetic energy, which is thermal motion rather than a large number of molecules moving together.

About 95-99 percent of diffusion through the gel occurs as rapidly as through the free fluid. For the short distance between capillaries and tissue cells, this diffusion allows rapid transport through the interstitial of not only water molecules but also electrolytes, molecular weight nutrients small, oxygen, carbon dioxide, ...

Free translation in the interstitial space

Although nearly all interstitial fluid is normally trapped within the gel tissue, occasional small streams of free fluid and vesicles are also present, meaning that the fluid is devoid of proteoglycan molecules and so can flow freely.

When a dye is injected into the circulating blood, it can often be seen flowing through the small interstitial space, usually along the surfaces of collagen fibres or the surfaces of cells.

The presence of free fluid in normal tissues is minimal, usually less than 1 percent. In contrast, when tissues are oedematous, the vesicles and small interstitial flow of free fluid greatly expand until half or more of the oedematous fluid flows freely independent of the proteoglycan fibrils.