Pericytes are contractile cells that wrap around the endothelial cells of capillaries and venules throughout the body. Also known as Rouget cells or mural cells, pericytes are embedded in basement membrane where they communicate with endothelial cells of the body's smallest blood vessels by means of both direct physical contact and paracrine signaling. In the brain, pericytes help sustain the blood–brain barrier as well as several other homeostatic and hemostatic functions of the brain. These cells are also a key component of the neurovascular unit, which includes endothelial cells, astrocytes, and neurons. Pericytes regulate capillary blood flow, the clearance and phagocytosis of cellular debris, and the permeability of the blood–brain barrier. Pericytes stabilize and monitor the maturation of endothelial cells by means of direct communication between the cell membrane as well as through paracrine signaling. A deficiency of pericytes in the central nervous system can cause the blood–brain barrier to break down.