Answer
Arterial blood is supplied to the brain by the internal carotid and the vertebral arteries. Venous drainage is through the dural sinuses to the internal jugular vein, thence to the subclavian, brachiocephalic and superior vena cava.
Work Step by Step
The blood brain barrier costs of the epithleal cells f the capillaries of the brain and the thich basement membrane of this endo theliu. The tightt junctions of the epitelial cells plus surrounding ependymal cells fom selective permeable structure called the blood brain barrier(BBB). Tis barrier is reinforced by secretions of astroglia. Some water soluble substances like glucose are taken through the BBB by active transport. Other substances like creatinine, urrea, and most ions pass through with difficulty. Lipid soluble substances--alcohol, oxygen carbon dioxide and certain anesthetics can also penetrate the blood brain barrier. However, proteins and most antibiotics are excluded by the BBB.
The importance of the BBB is that it protects the brain from pathogens, toxins and other harmful substances. It does, however, let in glucose and oxygen ;an adequate supply of each is needed constantly if full consciousness is to be maintained.
