Endothelium

Endothelium is a layer of cells that line the walls of the circulatory system which carries blood around the body. The cells form a membrane so that certain substances, such as nutrients, can move through the walls. In an adult human there is about 1 kg of endothelium cells, which would cover an area of about  7m2. The endothelium plays an important part in controlling the flow of blood around the body.

References

Category:Anatomy of the cardiovascular system