Pericyte, Astrocyte and Basal Lamina Association with the Blood Brain Barrier (BBB). The periendothelial accessory structures of the BBB include pericytes, astrocytes, and a basal membrane. The endothelial cells of the BBB are distributed along the length of the vessel and completely encircles the lumen. A thin basement membrane (i.e. basal lamina) supports the ablumenal surface of the endothelium.