Which part of the nephron is mainly responsible for ultrafiltration under high hydrostatic pressure?

• A. Bowman's capsule
• B. Proximal tubule
• C. Loop of Henle
• D. Glomerulus capillaries

Answer: (D)

Ultrafiltration under high hydrostatic pressure occurs most effectively in the glomerulus capillaries. These specialized, fenestrated capillaries create the glomerular filtration barrier that sits between the blood and Bowman's space. The high hydrostatic pressure here—driven by the larger inflow (afferent arteriole) and narrower outflow (efferent arteriole)—pushes water and small solutes across the barrier into Bowman's space. Bowman's capsule simply collects this filtrate; it doesn’t generate or drive filtration. The proximal tubule and Loop of Henle are mainly involved in reabsorption and concentration after filtration, not the filtration process itself. So the glomerulus capillaries are the site responsible for ultrafiltration under high hydrostatic pressure.