USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

Which phase is responsible for the descent of the testis to the lower abdomen or pelvic brim?

1. Abdominal phase

2. Transabdominal phase

3. Scrotal phase

4. Androgen-dependent phase

The correct answer is: Transabdominal phase

The transabdominal phase is essential for the initial descent of the testis during fetal development. During this phase, typically occurring between the 10th and 15th weeks of gestation, the testes begin their journey from their original position near the developing kidneys to the lower abdomen. This movement is primarily guided by the gubernaculum, a fibrous cord that helps anchor the testes and direct their descent. This phase involves the interaction of various factors, including hormonal influences such as insulin-like 3 (INSL3) produced by Leydig cells. This hormone is crucial for the growth and stabilization of the gubernaculum, facilitating the downward movement of the testes towards the pelvic brim. This phase sets the stage for subsequent phases of descent, including the scrotal phase, which happens later and is driven by different mechanisms, particularly those involving androgens. Understanding the transabdominal phase is crucial in the context of conditions like cryptorchidism, where failure of testicular descent can lead to infertility and increased risk of testicular cancer if not corrected.