Which description correctly matches capillary types and their permeability?

• A. Continuous capillaries have uninterrupted endothelium with tight junctions; fenestrated capillaries have endothelial pores; sinusoidal capillaries have wide gaps and discontinuous basal lamina.
• B. Continuous capillaries have wide gaps; fenestrated have no pores; sinusoidal have tight junctions.
• C. Fenestrated capillaries have no pores; continuous capillaries have large gaps; sinusoidal have complete basal lamina.
• D. Sinusoidal capillaries are the most restrictive with no gaps.

Answer: (A)

Capillary permeability is governed by the endothelial arrangement: continuous capillaries have an intact lining with tight junctions that limit paracellular flow; fenestrated capillaries possess endothelial pores (fenestrae) that increase permeability to small solutes while keeping a basal lamina; sinusoidal capillaries have large gaps between endothelial cells and a discontinuous basal lamina, allowing passage of larger molecules and even cells. This exactly matches the description that continuous capillaries have uninterrupted endothelium with tight junctions, fenestrated capillaries have endothelial pores, and sinusoidal capillaries have wide gaps and a discontinuous basal lamina. In tissues like the brain, continuous capillaries are highly restrictive; in the kidneys and intestinal mucosa, fenestrated capillaries enhance filtration and absorption; in the liver, spleen, and bone marrow, sinusoidal capillaries’ leaky structure accommodates larger molecules and cells. The other statements conflict with these features—continuous capillaries do not have wide gaps, fenestrated capillaries do have pores, and sinusoidal capillaries do not have a complete basal lamina and are not the most restrictive.