What are endothelial cells?

Blood vessel liners: There are very flat cells that line the entire inside of your circulatory system. They look like fried eggs, sunny-side-up with the nucleus being the yolk. A capillary is a long row of these rolled into a tube with a little fibrous reinforcement. Despite their simplicity, they keep your blood from clotting when it shouldn't and provide a perfect barrier for what shouldn't leave your blood.

Lining: Endothelial cells form a thin layer of lining of blood and lymphatic vessels. They are responsible for preventing your blood from clotting as it travels around the body, and have various other functions. Dysfunction of these cells plays a role in numerous diseases and can affect all parts of the body.