The internal male reproductive organs work collectively to produce, nourish, transport, and maintain vital reproductive fluids and gametes. Located primarily within the pelvic cavity and scrotum, these structures include the testes, a system of connecting ducts, and specialized accessory glands. Together, they ensure the safe delivery of viable sperm during copulation while supporting endocrine functions critical for male development and fertility.
The testes serve as the primary male gonads, housed safely inside the temperature-regulated scrotum. Each testis contains tightly coiled seminiferous tubules where sperm production takes place through meiosis. Interstitial cells, known as Leydig cells, sit between these tubules and secrete testosterone, the main male sex hormone driving secondary sexual characteristics and spermatogenesis.
Once generated in the seminiferous tubules, immature sperm move into the epididymis, a comma-shaped organ resting along the posterior surface of each testis.
The ductus deferens, or vas deferens, is a thick muscular tube that transports sperm from the epididymis upward through the inguinal canal into the pelvic cavity. It loops over the urinary bladder and expands into an ampulla before merging with the duct of the seminal vesicle to form the short ejaculatory duct. This paired duct penetrates the prostate gland, emptying its contents directly into the prostatic urethra during ejaculation.
Accessory glands secrete fluid that mixes with sperm to create functional semen.
Semen is a complex, alkaline fluid composed of sperm cells and secretions from the seminal vesicles, prostate, and bulbourethral glands. The alkalinity helps protect sperm by neutralizing the naturally acidic environment of the female reproductive tract. Semen initially coagulates after ejaculation due to clotting proteins, and then liquefies shortly after via enzymatic action, allowing sperm to swim freely toward the oocyte.
The hypothalamus releases gonadotropin-releasing hormone (GnRH), which stimulates the anterior pituitary gland to secrete luteinizing hormone (LH) and follicle-stimulating hormone (FSH). LH triggers Leydig cells to produce testosterone, while FSH acts on Sertoli cells within the seminiferous tubules to support spermatogenesis. A negative feedback loop involving testosterone and inhibin regulates this axis, keeping hormone levels balanced.