Where does urine formation begin in the kidney?

• A. Renal pelvis
• B. Renal tubule
• C. Glomerulus
• D. Collecting duct

Answer: (C)

Urine formation begins with filtration at the glomerulus. The glomerulus is a tuft of capillaries inside Bowman's capsule where blood plasma is forced through a filtration barrier into Bowman's space, producing the initial filtrate that will become urine after further processing along the nephron. This filtration is driven by the pressure differences across the barrier formed by the endothelial cells, basement membrane, and podocytes with slit diaphragms. After this first step, the filtrate moves into the renal tubules for reabsorption and secretion, and then into the collecting ducts before it becomes urine that drains into the renal pelvis. The renal pelvis is simply a collection area for urine, not a site where filtration occurs.