Endothelial cells
Endothelial cells line all blood vessels and lymphatics. They control the passage of materials and white blood cells into and out of the blood stream.
Endothelial cells are able to adapt and arrange themselves to suit local requirements. They extend to nearly every region of the body by cell migration, thus allowing to both extend and remodel the blood vessel network. It is because of endothelial cells that tissue growth and repair is possible.
References
Alberts et al. (2008) Molecular biology of the cell, 5th edition, New York: Garland Science.