What capillaries have endothelial cells pierced by filtration pores that allow the rapid passage of small molecules?

The answer here is "fenestrated". Fenestrated capillaries have pores in the endothelial cells that are covered with a diaphragm of radially oriented fibrils and permit little amount of molecules and partial amounts of protein to diffuse. They are 60 to 80 nanometers in diameter.