What process forces small molecules from the blood into Bowman's capsule under high hydrostatic pressure?

• A. Ultrafiltration
• B. Reabsorption
• C. Secretion
• D. Dialysis

Answer: (A)

Ultrafiltration is the process that forms the filtrate by using the high hydrostatic pressure in the glomerular capillaries to push water and small solutes across the filtration barrier into Bowman's capsule. This selective barrier prevents large molecules like proteins and blood cells from passing, so they stay in the bloodstream. Reabsorption happens later, when substances are taken back from the filtrate into the blood along the tubules. Secretion adds additional substances from blood into the filtrate in other parts of the nephron. Dialysis is an artificial filtration method outside the body.