Final answer:
Fenestrated cells are found in the capillary endothelium of the glomerulus, which is a component of the filtration membrane in the kidneys. They enable selective filtration based on the size and charge of substances, thus playing a critical role in the formation of urine.
Step-by-step explanation:
The component of the filtration membrane that possesses fenestrated cells is the capillary endothelium of the glomerulus in the kidneys. These fenestrated cells are crucial as they allow the passage of certain substances based on their size and charge, permitting the filtration of blood and the subsequent formation of urine.
Fenestrations are small pores within the endothelial cells of the capillaries that enable the selective passage of substances. These fenestrated endothelial cells are part of the renal corpuscle and play a key role in the kidney's ability to filter blood and excrete waste. The presence of these fenestrations aids in the filtration process by allowing substances less than 4 nm to cross readily, and most substances up to 8 nm to pass freely, while also considering their electric charge. The negatively charged proteins associated with these pores repel negatively charged substances and favor the passage of positively charged substances.
In summary, fenestrated capillary endothelial cells are integral to the formation of filtrate in the kidneys, working in conjunction with other components such as podocytes and the basement membrane to ensure that cells and large proteins are retained in the bloodstream, while smaller molecules are filtered into Bowman's capsule to ultimately become urine.