The lumbar plexus lies within the substance of the psoas major muscle and its branches have to emerge from the psoas major to reach their final destination. The following branch of lumbar plexus emerges from the medial border of the muscle:

Correct Answer: D

Rationale: Obturator nerve exits the psoas major medially to innervate adductors, unlike iliohypogastric/ilioinguinal (lateral), genitofemoral (anterior), or femoral (lateral). This distinguishes lumbar plexus anatomy, key for surgical approaches, contrasting with other trajectories.

Correct Answer: A

Rationale: Mesonephros cranial to ureteric bud forms male genital ducts (epididymis, vas) not female, paramesonephric (Mullerian), or utricle (sinus derivative). This distinguishes embryonic urogenital development, key for sex differentiation, contrasting with female structures.

Correct Answer: C

Rationale: Most renal calculi (75-85%) are calcium oxalate or phosphate not cystine (rare), urate (less common), or mixed. This distinguishes stone composition, vital for treatment, contrasting with minority types.

Correct Answer: D

Rationale: Acetohydroxamic acid prevents stones (inhibits urease in struvite cases), not causes them therapeutic role. Topiramate (anticonvulsant) alkalinizes urine, forming calcium phosphate stones. Triamterene (diuretic) crystallizes directly drug stones. Ephedrine (stimulant) links to stones via dehydration risk factor. Acetohydroxamic's preventive action distinguishes it, critical for infection stones, unlike stone-inducing drugs.

Correct Answer: D

Rationale: Serotonin typically inhibits erection counteracts arousal, not a promoter. Dopamine enhances desire and erection (central). Oxytocin supports penile response (peripheral). Nitric oxide (NO) drives vasodilation key mediator. Serotonin's inhibitory role distinguishes it, critical for understanding erectile balance, unlike facilitatory neuropeptides.