Clinical meaning
Male infertility evaluation requires systematic assessment of the hypothalamic-pituitary-gonadal axis, testicular function, and reproductive tract integrity. Spermatogenesis occurs within seminiferous tubules over a 72-day cycle, orchestrated by Sertoli cells (FSH-dependent) and supported by intratesticular testosterone produced by Leydig cells (LH-dependent). The blood-testis barrier formed by Sertoli cell tight junctions creates an immunologically privileged environment essential for meiotic progression. Testosterone undergoes conversion to DHT (by 5-alpha reductase) and estradiol (by aromatase CYP19A1 in adipose tissue, brain, testes, and bone). The ratio of testosterone to estradiol modulates hypothalamic feedback and influences spermatogenesis. Pre-testicular causes (hypogonadotropic hypogonadism from pituitary tumors, Kallmann syndrome, functional suppression from obesity, opioids, or exogenous androgens) are potentially reversible with hormonal stimulation. Testicular causes (Klinefelter syndrome, Y-microdeletions, gonadotoxic exposure, varicocele-induced oxidative stress) have variable prognosis. Post-testicular causes (CBAVD, ejaculatory duct obstruction, retrograde ejaculation) may be amenable to surgical correction or sperm retrieval. The clinician must order and interpret hormonal panels and semen analyses, prescribe pharmacotherapy targeting the specific pathophysiology, coordinate surgical referrals, and counsel on prognosis and assisted reproductive technology options.