Which component of the nephron is responsible for filtration?

The glomerulus is the key structure responsible for the filtration process in the nephron. It is a network of capillaries located at the beginning of the nephron, specifically within Bowman's capsule. During filtration, blood enters the glomerulus, and due to the high pressure in these capillaries, water and small solutes (such as ions, glucose, and urea) are pushed through the porous capillary walls into Bowman's capsule, forming what is known as the filtrate. This initial filtrate does not contain large molecules like proteins or blood cells because their size prevents them from passing through the filtration barrier.

Bowman's capsule, while it encases the glomerulus and collects the filtrate, is not the component that actively filters the blood; it is merely a receiving structure. The proximal tubule is involved in the reabsorption of nutrients and water from the filtrate after filtration has already taken place. The collecting duct plays a crucial role in the final concentration and regulation of urine, but it does not contribute to the initial filtration of blood. Therefore, the glomerulus is distinctly recognized as the filtration component of the nephron.