What are the small pores in the capillary endothelium called that contribute to the filtration membrane?

The small pores in the capillary endothelium that contribute to the filtration membrane are known as fenestrations. Fenestrated capillaries are characterized by having tiny openings or pores in their endothelial cells, which facilitate the passage of fluids and small solutes while limiting the passage of larger molecules and blood cells. This structural feature is crucial in the kidneys, particularly in the glomeruli, where filtration occurs.

In the context of the filtration membrane, these pores allow for effective filtration by permitting water and small solutes to pass through while retaining larger components of blood such as proteins and red blood cells. The presence of fenestrations thus plays a vital role in the selective filtration process essential for urine formation and maintaining homeostasis in the body.