For a long time, it was thought that endothelial cells served only to lining the inner surface of vessel walls. We now know that they are highly active cells that function as an independent organ.
The old rule of thumb is that a person's age is determined by the age of their blood vessels. Now we know what keeps blood vessels young and prevents dangerous spasms. It is the cells of the inner wall of blood vessels, the so-called endothelial cells.
Not just a lot of endothelial cells
The endothelium — is the boundary through which all substances for further transmission in the body arrive. Endothelial cells provide a regulated exchange of substances between the blood and the surrounding tissue cells through narrow channels and lumens. Electrolytes, fats and glucose pass through the tissue cell wall. In the same way, the immune system cells required in the neighboring tissue are transported. Normal metabolism ensures proper supply and functioning of all organs. This, in addition, reduces the risk of cardiovascular disease.
In the brain, the endothelial cells are so tightly interconnected through what are known as dense contacts that it is virtually impossible for large molecules to penetrate between the cells. This barrier of endothelial cells is called the blood-brain barrier. Fat-soluble substances, oxygen and carbon dioxide can, if necessary, pass through this barrier. All other substances, such as sugar, hormones or electrolytes, require special transport proteins, such as the vascular endothelial growth factor VEGF for glucose, to pass through the barrier.
In other parts of the body, the permeability of the endothelial layer is higher. Additional pores between endothelial cells are present in all organs where filtration, excretion and absorption of various substances take place. For example, in the kidneys, gastric mucosa or endocrine glands.
The interstitial wall limits the permeability to water, small molecules and water-soluble substances. In organs with rapid circulation of fluids and blood, such as the liver and bone marrow, there is no intermediate wall. Here the space between the endothelial cells is even greater. Compared to crossing the blood-brain barrier, substances penetrate the endothelial layer in these organs about 100 times faster.
Blood circulation control
The fact that the endothelium has significantly more functions is confirmed by its effect on blood flow. On the surface of the endothelial cells there are small sensors that are in constant contact with the blood flow.
They continuously record the characteristics of the blood flow and the substances entering it. However the endothelial cells not only monitor the blood flow along them but also react to the information they receive. When blood flow characteristics change, for example, when there is a lack of oxygen (hypoxia), the endothelial cells release a highly reactive substance — nitric oxide. This gas promotes vasodilatation as it passes through the endothelium in a few seconds and ensures that the adjacent layer of muscle tissue relaxes. This leads to a decrease in vascular pressure and a drop in blood pressure. This accelerates blood movement in the body and ensures its flow to the smallest vessels.
Optimal protection for blood vessels
Healthy endothelial cells — the best remedy against aging: if they are able to produce enough nitric oxide, the blood vessels remain young. Благодаря ему сохраняется их эластичность и способность к адаптации. This gas also prevents blood components from sticking to the inner wall of the vessel, as it helps keep it smooth and flexible.
Nitric oxide should be used to help repair damaged blood vessels. For example, interval hypoxic training is used to produce it. Exercise increases nitric oxide production and helps all patients who already have symptoms of atherosclerosis and type 2 diabetes. In both cases, nitric oxide production is significantly limited.
In inflammatory processes, the endothelium assumes a kind of mediating function. Because infections and cellular remodeling rarely occur in blood vessels, the endothelium simply keeps the leukocytes circulating in the bloodstream in their proper place. They remain on the inner wall of the vessel and are transported from there to the tissues below to fight the infection.
Stimulation of the formation of new blood vessels
New blood vessels are formed in the body even after birth. Endothelial cells are actively involved in their formation because they initiate this process by producing vascular endothelial growth factor VEGF.
The process of making new blood vessels is known medically as angiogenesis. This process is not understood as a collection of disparate elements, but as a complete system that continuously controls the proper supply and function of all organs.
When blood flow is disrupted, such as through injury or a blood disorder, or during exercise, the endothelial cells are activated. Muscle growth requires more blood flow, which means a more extensive capillary network.
Hypoxia provides the strongest impetus for vascular growth. It doesn't matter whether the lack of oxygen is limited to individual muscle groups or occurs throughout the body, such as during a trip to the mountains or during a hypoxic workout. Once tissue cells stop receiving enough oxygen, hypoxia-inducible factor (HIF) activation occurs, which stimulates vascular formation via vascular endothelial growth factor VEGF.
Coronavirus and sugar — enemies of the endothelium
Endothelial cells are very sensitive to sugar. Under its influence proteins stick together and harden in the vessel wall, which leads to constant disruption of its functioning. Doctors call the process of &lquo;sugarization» proteins glycation. The effects of excessive candy consumption can occur in both healthy and diabetic individuals. They lead to aging and can cause a range of complications in diabetes.
Belly fat also affects endothelial cell activity. Along with hormones, it produces pro-inflammatory cytokines in large quantities. These trigger a chronic inflammatory process that goes undetected for a long time. This slow but dangerous process adversely affects the function of endothelial cells. It leads to changes in their permeability and increases the likelihood of deposits on the vessel walls.
New «enemy » endothelium became coronavirus. After entering the blood through the lungs, it has a devastating effect on the walls of blood vessels. It can damage or even completely destroy endothelial cells. The supply of oxygen and nutrients to the organs deteriorates to the point of complete cessation and so called multiple organ failure. In studies, blood clots in the blood vessels of various organs and inflammation of the inside of blood vessels were found in people who died from the coronavirus. The endothelial cells of the lungs, heart and intestines suffered the most severe destruction. Many of those examined had a history of diseases associated with endothelial damage, such as hypertension, diabetes or obesity.