These cells have unique functions that include fluid filtration, such as in the glomerulus of the kidney, blood vessel tone, hemostasis, neutrophil recruitment, and hormone trafficking.

In straight sections of a blood vessel, vascular endothelial cells typically align and elongate in the direction of fluid flow.

Excessive or prolonged increases in permeability of the endothelium, as in cases of chronic inflammation, may lead to tissue swelling (edema).

These pro- and antiangiogenic signals including integrins, chemokines, angiopoietins, oxygen sensing agents, junctional molecules and endogenous inhibitors.

[25] In contrast, inflammatory stimuli also activate NF-κB-induced expression of the deubiquitinase A20 (TNFAIP3), which has been shown to intrinsically repair the endothelial barrier.

[28] A further consequence of damage to the endothelium is the release of pathological quantities of von Willebrand factor, which promote platelet aggregation and adhesion to the subendothelium, and thus the formation of potentially fatal thrombi.

[31] A healthy diet abundant in fruits and vegetables has a beneficial impact on endothelial function, whilst a diet high in red and processed meats, fried foods, refined grains and processed sugar increases adhesion endothelial cells and atherogenic promoters.

[33] A Mediterranean diet has been found to improve endothelial function in adults which can reduce risk of cardiovascular disease.

The researchers from the University of Zurich and Harvard Medical School considered these findings to be a sign of a general endotheliitis in different organs, an inflammatory response of the endothelium to the infection that can lead or at least contribute to multi-organ failure in Covid-19 patients with comorbidities such as diabetes mellitus, hypertension and cardiovascular disease.

[40] In 1958, A. S. Todd of the University of St Andrews demonstrated that endothelium in human blood vessels have fibrinolytic activity.