Blood-brain barrier is formed by

The foot process of astrocytes along with the capillary endothelial cells and tight junctions between them form the BBB. The blood-brain barrier(BBB) protects the brain and spinal cord from potentially harmful substances while allowing the gases and nutrients to enter. The tight junction between the endothelial cells of blood capillaries forms the most impoant component. The following areas are devoid of BBB: pineal gland, posterior lobe of the pituitary, tuber cinerum, area postrema, wall of supraoptic recess of third ventricle. (Ref: clinical neuroanatomy by Vishram Singh, 2nd edition, pg- 183)