Which statement accurately describes urine formation?

Which statement accurately describes urine formation?

• A. Filtration occurs only in the renal medulla
• B. Reabsorption occurs exclusively in the urethra
• C. Secretion occurs only in the kidney
• D. Filtration occurs in the glomerulus of the nephron

Answer: (D)

The event being tested is where filtration—the first step of urine formation—occurs. Filtration happens in the glomerulus, a tuft of capillaries inside the nephron. Blood pressure forces plasma across the filtration barrier into Bowman's capsule, producing filtrate that contains water and small solutes but excludes cells and large proteins. This filtrate then moves through the renal tubules where reabsorption and secretion modify its composition before becoming urine. The urethra is simply the exit passage for urine, not a site of reabsorption. Secretion also occurs along the nephron, not exclusively in another location. So the precise statement is that filtration occurs in the glomerulus of the nephron.

The event being tested is where filtration—the first step of urine formation—occurs. Filtration happens in the glomerulus, a tuft of capillaries inside the nephron. Blood pressure forces plasma across the filtration barrier into Bowman's capsule, producing filtrate that contains water and small solutes but excludes cells and large proteins. This filtrate then moves through the renal tubules where reabsorption and secretion modify its composition before becoming urine. The urethra is simply the exit passage for urine, not a site of reabsorption. Secretion also occurs along the nephron, not exclusively in another location. So the precise statement is that filtration occurs in the glomerulus of the nephron.