Meaning of Endothelial Cells
Endothelial cells have a flat-shaped basophilic nucleus, which characterizes paved epithelial cells under light microscopy and is bluish in color, due to the affinity for hematoxylin in common HE preparations. The cytoplasm is not very bulky and often cannot be seen under the microscope.
The epithelium that lines the blood vessels, lymphatic vessels, and the heart internally is called the endothelium. It consists of a single layer of floor cells, called endothelial cells, and is therefore classified as simple floor epithelium.
These cells have their origin in the mesoderm and, although they form a very thin lining layer in the vessels and the heart, they cover an area of about 600 square meters in the entire cardiovascular and lymphatic system.
An endothelial cell lives about 30 years. After this period, the cells tend to die and neighboring cells proliferate and replace it.
Regenerating endothelial cells do not seem to fully fulfill their functions, so their response to stimuli is diminished.
Endothelial cells are not just lining cells
The endothelial cells of the blood vessels have several metabolic functions, therefore they are considered an interface between the circulatory system and the various systems of the body.
For many years it was believed that its function was limited to the characteristic lining of all other epithelia. However, in the last 40 years there have been several functions of the endothelium for the homeostasis of the organism. We can mention the following functions:
- It constitutes a smooth wall and, therefore, preserves the laminar blood flow, preventing the adhesion and aggregation of blood cells;
- It preserves the fluidity of the plasmatic membrane and the characteristic of the basement membrane, so that it controls the passage of substances between the vessels and the blood;
- It has modulation mechanisms between coagulation and fibrinolysis, that is, it acts on coagulation when there are ruptures in the vessels, but prevents this process in normal blood;
Inhibits cell proliferation and migration;
- Controls inflammation;
- It maintains vascular tone, but also has a vasodilator function. In this way, it adapts to the stimuli on the amount of blood needed in the tissues;
- Plays a protective role against the development of vascular lesions
- It regulates the response of the Autonomic Nervous System, through the vagal tone, that is, it controls vasodilation and vasoconstriction by order of the vagus nerve;
- It controls the growth of new vessels and vascular circuits necessary in certain situations, also regulating the proliferation of smooth muscle cells.
The functions of the endothelium are related to the production of certain substances by endothelial cells, under the stimulation of blood pressure in the vessels.
The main one is nitric oxide (NO). However, they produce other substances with a vasodilator function, such as prostacyclins, kinins, and endothelium-derived hyperpolarization factor, and others with a vasoconstrictor function, such as endothelin and angiotensin II.
In addition, antioxidant molecules such as the enzyme superoxide dismutase and anti-inflammatory molecules such as prostacyclins, heparans and natriuretic peptides are produced.
The balance between the production and release of these substances maintains the normal endothelium, but an imbalance in this production can lead to endothelial dysfunction and conditions such as arteriosclerosis.