A male fetus has undescended testes at 32 weeks gestation. Testicular descent from the posterior abdominal wall to the scrotum occurs in two phases. Which hormone drives the second inguinoscrotal phase of descent?

• A Testosterone (converted to dihydrotestosterone at the gubernaculum); androgen-driven condensation and shortening of the gubernaculum ✓
• B Insulin-like factor 3 (INSL3) secreted by Leydig cells drives both phases of descent
• C Müllerian inhibitory substance (MIS/AMH) drives inguinoscrotal descent via genitofemoral nerve
• D Gonadotropin-releasing hormone (GnRH) from the hypothalamus directly stimulates gubernacular regression

Explanation

Testicular descent occurs in two phases: (1) the transabdominal phase (weeks 8–15), driven by INSL3 (insulin-like factor 3) from Leydig cells causing gubernacular swelling and anchoring; and (2) the inguinoscrotal phase (weeks 25–35), driven by testosterone/DHT acting via the genitofemoral nerve (calcitonin gene-related peptide release from the nerve coordinates gubernacular regression and cremasteric reflex development). Testosterone is essential for inguinoscrotal descent; boys with androgen insensitivity have testes that do not descend into the scrotum. INSL3 is critical for transabdominal phase, not the inguinoscrotal phase specifically.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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