blood-brain barrier anatomical structure. semipermeable border that

anatomy vessels science nervous medicine human health cortex cerebral capillary medical blood barrier biology brain astrocyte pns neuro feet space supply end cranial cns capillaries virchow unit endothelial cell microscopical virchowrobin structure neurovascular tight junction bloodbrain endothelium vrs basal lamina bbb cross section anatomical semipermeable border circulating extracellular fluid neuron