The male reproductive system has three core functions: producing sperm, delivering sperm into the female reproductive tract, and producing testosterone. These functions depend on a coordinated network of organs, ducts, glands, and hormones that begin working at puberty and continue, with gradual changes, throughout life.
Sperm Production
Sperm are produced inside the testicles in tightly coiled structures called seminiferous tubules. The process, called spermatogenesis, takes 72 to 74 days from start to finish. It begins with precursor cells that divide repeatedly, first doubling their genetic material and then splitting it in half twice. The end result is a cell carrying exactly half the chromosomes needed for a complete human embryo. The other half comes from the egg at fertilization.
These early sperm cells start out round and immobile. They’re gradually reshaped into the streamlined form most people picture: a compact head carrying genetic material and a whip-like tail for propulsion. This transformation happens while the developing sperm are still nestled inside supportive cells in the tubule walls. Once released, the sperm move into the epididymis, a coiled tube sitting behind each testicle, where they spend additional time maturing and gaining the ability to swim.
Sperm production is continuous. New precursor cells divide throughout adult life, so the testicles are always generating fresh sperm at various stages of development.
Temperature Control for Sperm
Sperm production requires a temperature about 2 to 3 degrees Celsius below normal body temperature. That’s why the testicles sit outside the body in the scrotum rather than inside the abdomen. The scrotum is specifically built for heat regulation: its skin is thin, has almost no insulating fat underneath, carries relatively little hair, and contains more sweat glands than typical skin, all of which allow heat to escape easily.
The system also adjusts actively. In cold conditions, muscles in the scrotum contract, pulling the testicles closer to the body for warmth while the skin wrinkles to reduce its exposed surface area. In warm conditions, those muscles relax, letting the testicles hang lower and releasing more heat. A network of blood vessels called the pampiniform plexus plays a major role too, cooling arterial blood on its way to the testicles by running it alongside cooler venous blood heading back toward the body.
The Path Sperm Travel
From production to ejaculation, sperm pass through a specific sequence of structures. After leaving the testicles, they enter the epididymis for storage and maturation. From there, they move into the vas deferens, a muscular tube that carries them upward from the scrotum into the pelvic cavity. Each vas deferens joins with a duct from a nearby gland called the seminal vesicle to form a short ejaculatory duct. These ejaculatory ducts pass through the prostate gland and empty into the urethra, which runs through the penis to the outside of the body.
During ejaculation, muscular contractions propel sperm along this entire pathway in seconds. The urethra serves double duty in the male body, carrying both urine and semen, though never at the same time. A valve mechanism at the base of the bladder closes during ejaculation to prevent the two from mixing.
What Semen Is Made Of
Sperm cells themselves make up only a small fraction of semen’s total volume. The bulk of the fluid comes from accessory glands that add their secretions as sperm travel through the duct system.
- Seminal vesicles contribute roughly 60 percent of semen’s volume. Their fluid contains fructose (a sugar that serves as fuel for sperm), compounds that help sperm stay mobile and viable, and proteins that cause semen to thicken slightly after ejaculation.
- Prostate gland produces most of the remaining fluid. Its secretion is thin, milky, and alkaline, which helps neutralize the acidic environment of the female reproductive tract so sperm can survive longer.
- Bulbourethral glands contribute a small amount of alkaline, mucus-like fluid released before ejaculation. This pre-ejaculatory fluid lubricates the urethra and helps neutralize any residual acidity from urine.
Together, these fluids protect sperm, nourish them, and create favorable conditions for fertilization.
Hormone Production
The second major function of the male reproductive system is producing testosterone, the primary male sex hormone. Testosterone is made in specialized cells within the testicles, and its effects reach far beyond reproduction. It drives the development of secondary sex characteristics during puberty, including a deeper voice, facial and body hair growth, and increased muscle and bone mass. It also maintains sex drive and supports ongoing sperm production throughout adulthood.
Three hormones work together to regulate the entire system. The brain’s pituitary gland releases two signaling hormones: one that stimulates sperm production directly, and another that triggers the testicles to produce testosterone. Testosterone then feeds back to the brain, helping regulate how much of those signaling hormones get released. This feedback loop keeps sperm and hormone production relatively stable over time.
How the System Changes With Age
The male reproductive system doesn’t shut down at a defined age the way the female system does at menopause, but it does change gradually. Testicular tissue mass decreases over the years, and testosterone levels decline slowly. The tubes that carry sperm lose some of their elasticity.
Sperm production continues but slows. The volume of ejaculated fluid typically stays about the same, but it contains fewer living sperm. Some men notice a reduced sex drive, and sexual responses may become slower and less intense. These changes are linked to the gradual drop in testosterone, though the pace varies widely from person to person.