Fig. 2

Comparison between the Blood-CSF Barrier (BCSFB) and Blood–Brain Barrier (BBB) structures. The BBB separates the lumen of the brain capillaries from the brain parenchyma. The main contribution to the BBB property of reduced permeability comes from the tight junctions (TJs) among endothelial cells lining of the capillaries. The BCSFB is at each ventricle's choroid plexus epithelial cells, joined together by TJs. Unlike the endothelium in the brain parenchyma, capillaries of the choroid plexus have no TJs and are fenestrated; therefore, they are relatively leaky and permeable to small molecules. Although in principle, both the barriers serve the homologous defensive purpose for the CNS, their distinct anatomical feature allows the interchange of different substances between the CSF/bloodstream and the brain cells