What is the glomerulus in the nephron?

• A. A ball of capillaries surrounded by Bowman's capsule in the nephron and serving as the site of filtration.
• B. A network of tubules where urine is formed.
• C. A blood vessel carrying blood away from the kidney.
• D. A nerve cluster controlling filtration.

Answer: (A)

The glomerulus is a tuft of capillaries inside Bowman's capsule where filtration happens. Blood enters through the afferent arteriole and leaves via the efferent arteriole, creating pressure that pushes water and small solutes from the blood into Bowman's space, forming the filtrate. The filtration barrier—endothelial pores, a basement membrane, and podocyte diaphragms—prevents large proteins and cells from passing through. The surrounding Bowman's capsule then collects this filtrate to begin its journey through the rest of the nephron. This isn’t a tubular network where urine is formed, nor a vessel carrying blood away from the kidney, nor a nerve cluster controlling filtration.