What distinguishes fenestrated capillaries from continuous capillaries in renal filtration?

• A. Continuous capillaries have pores
• B. Fenestrated capillaries have pores
• C. Fenestrated in liver
• D. Both non-permeable

Answer: (B)

Fenestrated capillaries are characterized by pores (fenestrae) in their endothelial lining, which dramatically increases the ease with which fluids and small solutes can pass through. In the kidney, this helps plasma move from the glomerular capillaries into Bowman's space while keeping blood cells behind, so filtration can occur efficiently. Continuous capillaries, on the other hand, have an uninterrupted endothelial lining with tight junctions and a continuous basement membrane, making them more restrictive to passage. The liver’s capillaries are not fenestrated in the same sense—they’re sinusoidal (discontinuous) with large gaps—so the idea that fenestrated capillaries are defined by being in the liver isn’t reliable. Saying both types are non-permeable isn’t accurate, since capillaries are permeable to varying degrees, especially fenestrated ones. So, the key distinguishing feature is the presence of pores in fenestrated capillaries.