The human body is made up of many different cells. Organs and tissues are made up of some, and bones are made of others. In the structure of the circulatory system of the human body, endothelial cells play a huge role.
What is endothelium?
Endothelium (or endothelial cells) is an active endocrine organ. Compared to the rest, it is the largest in the human body and lines the vessels throughout the body.
According to the classical terminology of histologists, endothelial cells are a layer, which includes specialized cells that perform complex biochemical functions. They line the entire cardiovascular system from the inside , and their weight reaches 1.8 kg. The total number of these cells in the human body reaches one trillion.
Immediately after birth, the density of endothelial cells reaches 3500-4000 cells / mm 2 . In adults, this figure is almost two times lower.
Previously, endothelial cells were considered only a passive barrier between tissues and blood.
Existing Endothelium Forms
Specialized forms of endothelial cells have certain structural features. Depending on this, they distinguish:
- somatic (closed) endotheliocytes;
- fenestrated (perforated, porous, visceral) endothelium;
- sinusoidal (large porous, large-stone, hepatic) type of endothelium;
- ethmoid (intercellular fissure, sinus) type of endothelial cells;
- high endothelium in post-capillary venules (reticular, stellate type);
- endothelium of the lymphatic channel.
The structure of specialized forms of the endothelium
Somatic or closed type endotheliocytes are characterized by dense gap junctions, less commonly, desmosomes. In the peripheral areas of such an endothelium, the thickness of the cells is 0.1-0.8 microns. In their composition, one can notice numerous micropinocytotic vesicles (organoids storing useful substances) of a continuous basement membrane (cells that separate connective tissues from the endothelium). This type of endothelial cell is localized in the glands of external secretion, the central nervous system, heart, spleen, lungs, and large vessels.
Fenestrated endothelium is characterized by thin endotheliocytes in which through diaphragmed pores are present. The density in micropinocytotic vesicles is very low. A continuous basement membrane is also present. Most often, such endothelial cells are found in capillaries. The cells of this endothelium line the capillary channels in the kidneys, endocrine glands, mucous membranes of the digestive tract, and the vascular plexuses of the brain.
The main difference between the sinusoid type of vascular endothelial cells from the rest is that their intercellular and transcellular channels are very large (up to 3 ΞΌm). Discontinuity of the basement membrane or its complete absence is characteristic. Such cells are present in the vessels of the brain (they are involved in the transport of blood cells), the cortex of the adrenal glands and the liver.
Lattice endothelial cells are rod-shaped (or spindle-shaped) cells that surround the basement membrane. They also take an active part in the migration of blood cells throughout the body. The place of their localization is venous sinuses in the spleen.
The composition of the reticular type of endothelium includes stellate cells, which are intertwined with basolateral processes of a cylindrical shape. The cells of this endothelium transport lymphocytes. They are part of the vessels passing through the organs of the immune system.
The endothelial cells that are in the lymphatic channel are the thinnest of all types of endothelium. They contain an elevated level of lysosomes and larger vesicles enter their composition. There is no basement membrane at all, or it is intermittent.
There is also a special endothelium that lines the posterior surface of the cornea of ββthe human eye. Endothelial cells of the cornea transport liquid and dissolved substances into it, and also support its dehydrated state.
The role of the endothelium in the human body
Endothelial cells that line the inside of the walls of blood vessels have an amazing ability: they increase or decrease their number, as well as the location in accordance with the requirements of the body. Almost all tissues require blood supply, which in turn depends on endothelial cells. They are responsible for creating a very flexible life support system that branches out into all areas of the human body. Thanks to this ability of the endothelium to expand and restore the network of blood vessels, the healing process and tissue growth occur. Without this, wound healing would not have occurred.
Thus, endothelial cells lining all vessels (starting from the heart and ending with the smallest capillaries), ensure the passage of substances (including leukocytes) through tissues into the bloodstream, as well as back.
In addition, laboratory studies of embryos have shown that all large blood vessels (arteries and veins) are formed from small vessels, which are built exclusively from endothelial cells and basement membranes.
Endothelial function
First of all, endothelial cells support homeostasis in the blood vessels of the human body. The vital functions of endothelial cells include:
- They are a barrier between blood vessels and blood, being, in fact, a reservoir for the latter.
- Such a barrier has selective permeability, which protects the blood from harmful substances;
- The endothelium captures and transmits signals that are carried by the blood.
- It integrates, if necessary, the pathophysiological environment in the vessels.
- Performs the function of a dynamic controller.
- Controls homeostasis and restores damaged vessels.
- Maintains blood vessel tone.
- Responsible for vascular growth and remodeling.
- Detects biochemical changes in the blood.
- Recognizes changes in the level of carbon dioxide and oxygen in the blood.
- Provides blood flow by regulating the components of its coagulation.
- Control blood pressure.
- Forms new blood vessels.
Endothelial dysfunction
As a result of endothelial dysfunction, the following can develop:
- atherosclerosis;
- hypertonic disease;
- coronary insufficiency;
- myocardial infarction;
- diabetes and insulin resistance;
- renal failure;
- asthma;
- adhesive disease of the abdominal cavity.
All these diseases can only be diagnosed by a specialist, so after 40 years you should regularly undergo a full examination of the body.