What characteristic defines fenestrated capillary walls in the glomerulus?

Fenestrated capillary walls in the glomerulus are characterized by the presence of pores in the endothelial cells. These pores, or fenestrations, allow for increased permeability, enabling a more efficient filtration process as blood passes through the glomerulus. This feature is essential for the filtration of plasma and the formation of urine, as it facilitates the passage of water, ions, and small molecules while retaining larger components such as proteins and cells.

The structure of fenestrated endothelium is specifically designed to balance the need for filtration and the maintenance of a barrier to larger molecules, making it critical for the kidney's function in regulating blood composition and volume. Other options do not accurately reflect the distinctive structural characteristic of fenestrated capillaries, as they either describe features not present in the glomerulus or illustrate a different type of capillary not suited to its filtration role.