Which structure forms the blood-brain barrier that regulates substance passage between the bloodstream and neural tissue?

Which structure forms the blood-brain barrier that regulates substance passage between the bloodstream and neural tissue?

• A. Ependymal cells lining ventricles
• B. Choroid plexus epithelial cells
• C. Neurons in the cortex
• D. CNS capillary endothelial cells with tight junctions, supported by astrocyte endfeet

Answer: (D)

The blood-brain barrier is formed by the CNS capillary endothelium connected by tight junctions, with astrocyte endfeet wrapping around the vessels to support and regulate those junctions. These tight junctions create a selective barrier that limits paracellular diffusion, allowing only specific nutrients to pass via transporters. The astrocyte endfeet help maintain this barrier’s integrity and signaling. The other structures don’t form the BBB: ependymal lining and choroid plexus epithelium are involved in producing and regulating the CSF and form the blood-CSF barrier, not the BBB, and neurons themselves do not create a barrier.

The blood-brain barrier is formed by the CNS capillary endothelium connected by tight junctions, with astrocyte endfeet wrapping around the vessels to support and regulate those junctions. These tight junctions create a selective barrier that limits paracellular diffusion, allowing only specific nutrients to pass via transporters. The astrocyte endfeet help maintain this barrier’s integrity and signaling. The other structures don’t form the BBB: ependymal lining and choroid plexus epithelium are involved in producing and regulating the CSF and form the blood-CSF barrier, not the BBB, and neurons themselves do not create a barrier.