The right answer is the kidney (more precisely in the basement membrane of the glomerulus).
Glomerular filtration is the filtration of blood by the glomerulus of the kidney, leading to the formation of primitive urine.
It is carried out through the glomerulo-capillary wall composed of three layers: the vascular endothelium, the basement membrane and the urinary epithelium.
This wall has a high permeability, but it is selective.