The human body is made up of many different cells. Organs and tissues are made of some, and bones are made of others. Endothelial cells play a huge role in the structure of the circulatory system of the human body.
What is an endothelium?
The 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, endothelial cell density reaches 3500-4000 cells/mm2. In adults, this figure is almost two times lower.
Earlier, endothelial cells were considered only a passive barrier between tissues andblood.
Existing forms of endothelium
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-window, hepatic) type of endothelium;
- lattice (intercellular slit, sinus) type of endothelial cells;
- high endothelium in postcapillary venules (reticular, stellate type);
- endothelium of the lymphatic bed.
Structure of specialized forms of endothelium
Endotheliocytes of a somatic or closed type are characterized by dense gap junctions, less often - desmosomes. In the peripheral areas of such endothelium, the thickness of the cells is 0.1-0.8 µm. In their composition, one can notice numerous micropinocytic vesicles (organelles that store useful substances) of a continuous basement membrane (cells that separate connective tissues from the endothelium). This type of endothelial cell is localized in the exocrine glands, central nervous system, heart, spleen, lungs, and large vessels.
Fenestrated endothelium is characterized by thin endotheliocytes, in which there are through diaphragmatic pores. The density in micropinocytic vesicles is very low. A continuous basement membrane is also present. Most often, such endothelial cells are found in capillaries. These endothelial cells linecapillary beds in the kidneys, endocrine glands, mucous membranes of the digestive tract, choroid plexuses of the brain.
The main difference between the sinusoid type of vascular endothelial cells and the rest is that their intercellular and transcellular channels are very large (up to 3 microns). 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 are surrounded by a basement membrane. They also take an active part in the migration of blood cells throughout the body. Their localization is the venous sinuses in the spleen.
The composition of the reticular type of endothelium includes stellate cells that intertwine with cylindrical basolateral processes. The cells of this endothelium provide transport of lymphocytes. They are part of the vessels passing through the organs of the immune system.
Endothelial cells, which are found in the lymphatic system, are the thinnest of all types of endothelium. They contain an increased level of lysosomes and are composed of larger vesicles. There is no basement membrane at all, or it is discontinuous.
There is also a special endothelium that lines the posterior surface of the cornea of the human eye. The endothelial cells of the cornea transport fluid and solutes into the cornea and keep it dehydrated.
Roleendothelium in the human body
Endothelial cells, which line the walls of blood vessels from the inside, 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 need blood supply, which in turn depends on endothelial cells. They are responsible for creating a highly adaptable life support system that branches out into all areas of the human body. It is thanks to this ability of the endothelium to expand and restore the network of blood supply vessels that the process of healing and tissue growth occurs. Without it, wound healing would not occur.
Thus, endothelial cells lining all vessels (from the heart to the smallest capillaries) ensure the passage of substances (including leukocytes) through the tissues into the blood and back.
In addition, laboratory studies of embryos have shown that all large blood vessels (arteries and veins) are formed from small vessels that are built exclusively from endothelial cells and basement membranes.
Endothelial functions
First of all, endothelial cells maintain homeostasis in the blood vessels of the human body. The vital functions of endothelial cells include:
- They are a barrier between 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 picks up and transmits signals 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 the tone of blood vessels.
- Responsible for the growth and remodeling of blood vessels.
- Detects biochemical changes in the blood.
- Recognizes changes in carbon dioxide and oxygen levels in the blood.
- Provides blood fluidity by regulating blood clotting components.
- Control blood pressure.
- Forms new blood vessels.
Endothelial dysfunction
As a result of endothelial dysfunction may develop:
- atherosclerosis;
- hypertension;
- coronary insufficiency;
- myocardial infarction;
- diabetes and insulin resistance;
- kidney failure;
- asthma;
- abdominal adhesive disease.
All these diseases can only be diagnosed by a specialist, so after the age of 40, you should regularly undergo a complete examination of the body.
