Most tubular re-absorption occurs at the

Correct Answer: C

Rationale: Proximal convoluted tubule (PCT) reabsorbs ~65-70% of filtrate (glucose, Na+), not loop, DCT (fine-tuning), or glomerulus (filtration). This highlights PCT dominance, vital for bulk reabsorption, contrasting with later segments.

Correct Answer: D

Rationale: Secretion moves substances from peritubular capillaries to DCT, not loop, glomerulus (filtration), or vasa recta (exchange). This defines secretion pathway, vital for drug elimination, contrasting with reabsorption.

Correct Answer: D

Rationale: External urethral sphincter is voluntary (skeletal muscle), unlike urethra (tube), detrusor (involuntary), or internal sphincter (smooth). This identifies micturition control, vital for continence, contrasting with involuntary structures.

Correct Answer: D

Rationale: Descending limb fluid becomes hypertonic as water exits into concentrated medullary interstitium, not isotonic/hypotonic. This describes countercurrent effect, vital for urine concentration, contrasting with initial states.

Correct Answer: C

Rationale: Capillary hydrostatic pressure (glomerulus) drives filtration, not filtrate pressure (opposes) or osmotic (retains). This identifies filtration force, key for GFR, contrasting with opposing pressures.