Which description correctly contrasts the blood-brain barrier with systemic capillaries?

Which description correctly contrasts the blood-brain barrier with systemic capillaries?

• A. BBB is fenestrated; systemic capillaries are continuous.
• B. Both have the same permeability.
• C. BBB is continuous with low permeability; systemic capillaries are fenestrated or sinusoidal.
• D. BBB has no permeability barrier at all.

Answer: (C)

The main idea is how the barrier properties of brain vessels differ from those of typical systemic capillaries. The blood-brain barrier consists of brain capillaries with a continuous endothelium joined by tight junctions, supported by astrocyte end-feet and pericytes. This setup creates very low paracellular permeability and highly selective transport—only certain substances cross easily via specific carriers or pumps. In contrast, systemic capillaries vary in structure: some are continuous, but others are fenestrated with small pores, or sinusoidal with larger gaps. These features allow much greater exchange of fluids and solutes. So describing the BBB as continuous with low permeability, while systemic capillaries are fenestrated or sinusoidal, accurately contrasts their permeability and structural differences.

The main idea is how the barrier properties of brain vessels differ from those of typical systemic capillaries. The blood-brain barrier consists of brain capillaries with a continuous endothelium joined by tight junctions, supported by astrocyte end-feet and pericytes. This setup creates very low paracellular permeability and highly selective transport—only certain substances cross easily via specific carriers or pumps. In contrast, systemic capillaries vary in structure: some are continuous, but others are fenestrated with small pores, or sinusoidal with larger gaps. These features allow much greater exchange of fluids and solutes. So describing the BBB as continuous with low permeability, while systemic capillaries are fenestrated or sinusoidal, accurately contrasts their permeability and structural differences.