Endothelial cells are a specialized type of body cell that lines the internal surface of all parts of circulatory system, such as the heart, arteries, veins, and capillaries. Endothelial cells are simple squamous epithelium, meaning they have a flat shape are are arranged in a single layer of cells. The endothelial cells provide a smooth surface to keep blood flowing quickly throughout the body, and help prevent blood clots from forming within the circulatory system.
The structure formed by the enothelial cells is called the endothelium. The endothelium within the heart is more specifically known as the endocardium. Endothelial cells differ from other epithelial cells in that the cytoskeleton, which provides internal structure to the cell, includes vimentin protein filaments rather than keratin filaments.
The endothelium is responsible for many essential biological functions. It is involved in vasodilation and vasoconstriction, the control of blood pressure through changes in the diameter of the blood vessels, widening them to increase blood flow and constricting them to reduce blood flow. When damaged, the endothelium begins the process of blood clotting, or coagulation, to repair the injury and prevent hemorrhage. Endothelial cells are also involved in angiogenesis, the formation of new blood cells. They are also part of in the immune response and help control the passage of white blood cells into and out of the blood stream, and they engage in more specialized filtration in certain organs, such as the brain and kidney.
The endothelium is also involved in certain disorders, including atherosclerosis, the thickening of the arterial walls due to the buildup of cholesterol or other fatty materials. Dysfunction of the endothelium, characterized by, for example, impaired vasodilation and vasoconstriction, is often an early warning sign of heart problems or atherosclerosis. Endothelial dysfunction is also common in cigarette smokers and in patients with diabetes mellitus, coronary artery disease, high blood pressure, and hypercholesterolemia, or high cholesterol levels in the blood.