A 21-year-old man undergoes a routine pre-employment physical examination. During testicular examination, he is found to have only 1 testis in his scrotum. Further evaluation reveals an elevated serum FSH level and a normal serum LH level. Production of which of the following substances is likely to be impaired in this patient?

Question

A 21-year-old man undergoes a routine pre-employment physical examination.  During testicular examination, he is found to have only 1 testis in his scrotum.  Further evaluation reveals an elevated serum FSH level and a normal serum LH level.  Production of which of the following substances is likely to be impaired in this patient?

Quizplus · Accepted Answer

11ec160b_3ca8_8136_9249_f73f272f9670_MD0001_00 Pulsatile secretion of gonadotrophin-releasing hormone (GnRH) from the hypothalamus stimulates the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Both FSH and LH are produced by the gonadotroph cells of the anterior pituitary. LH stimulates the release of testosterone from the Leydig cells of the testes; FSH stimulates the release of inhibin B from the Sertoli cells of the testes. Testosterone has a negative feedback effect on LH and GnRH secretion, and inhibin B suppresses FSH secretion. Sertoli cells are present within the seminiferous tubules of the testes. In patients with 1 testicle, the mass of Sertoli cells is significantly reduced. Therefore, the circulating levels of inhibin B are likely to be low in these patients. Low inhibin B levels will not provide adequate negative feedback on FSH secretion, thus FSH levels will tend to be elevated in males who only have 1 testicle. A male patient of any age who has only 1 testicle requires further evaluation. Since there is an increased cancer risk in men with an undescended testicle, most of these "abdominal testicles" are either removed (orchiectomy) or receive surgery that allows descent into the scrotum (orchiopexy). (Choices A, B, and C) Although the number of Leydig cells is reduced when only 1 testicle is present, androgen levels are not affected due to compensation by the remaining Leydig cell mass. Additionally, this patient has a normal LH level, indicating that there is adequate androgenic feedback to the hypothalamus and pituitary. Testosterone, dihydrotestosterone, and DHEA cause LH feedback inhibition, but they are not part of the FSH feedback loop. (Choice E) Cortisol has no direct relationship with LH and FSH secretion. High circulatory levels of cortisol, however, do produce hypogonadotropic hypogonadism by suppressing the release of gonadotrophin-releasing hormone. Educational objective: Inhibin B is produced by the Sertoli cells and is the physiological inhibitor of FSH secretion. LH concentration is controlled primarily by testosterone feedback.

A 21-Year-Old Man Undergoes a Routine Pre-Employment Physical Examination