The male reproductive system is a group of organs that work together to produce sperm, deliver it during intercourse, and manufacture the hormones responsible for male physical development. Some of these organs sit outside the body, while others are internal. Together, they form a tightly coordinated system driven by hormonal signals from the brain.
External Organs
The most visible parts of the male reproductive system are the penis, scrotum, and testicles. Each plays a distinct role in reproduction.
The testicles are two oval-shaped organs, roughly the size of large olives, that produce both sperm and testosterone. They hang inside the scrotum, a loose pouch of skin behind the penis. The scrotum acts as a biological thermostat: sperm production requires a temperature slightly below core body temperature (around 97 to 99°F), so muscles in the scrotal wall contract to pull the testicles closer to the body for warmth or relax to let them hang lower for cooling. This constant adjustment keeps conditions right for healthy sperm development. Each testicle is held in place and supplied with blood by a structure called the spermatic cord.
The penis serves as the organ for both urination and sexual intercourse. During arousal, spongy tissue inside it fills with blood, producing an erection that allows sperm to be deposited in the female reproductive tract.
Internal Organs and Accessory Glands
Several internal structures transport, nourish, and protect sperm on their journey out of the body. The vas deferens is a muscular tube that carries sperm away from the testicles. The urethra runs through the penis and serves as the shared exit route for both urine and semen, though never at the same time.
Three sets of glands add fluid to sperm to create semen, and each gland contributes something different. The seminal vesicles produce about 60% of semen’s total volume. Their secretion is thick and rich in fructose (a sugar that gives sperm energy), along with compounds that help sperm move and stay viable. The prostate gland contributes most of the remaining volume with a thin, milky, alkaline fluid that further supports sperm motility. The bulbourethral glands add only a small amount of fluid, but it plays an important preparatory role: it neutralizes leftover acidity in the urethra from urine and helps reduce acidity in the vagina during intercourse, creating a more hospitable environment for sperm.
The epididymis, a coiled tube sitting behind each testicle, is where newly formed sperm mature and are stored until ejaculation. Sperm that leave the testicles aren’t yet capable of swimming on their own. They gain that ability during their time in the epididymis.
How Sperm Are Made
Sperm production, called spermatogenesis, takes place inside the testicles and is a surprisingly slow process. A single sperm cell takes roughly 72 to 74 days to develop from start to finish. Production runs continuously from puberty onward, so new sperm are always at various stages of development.
Two specialized cell types inside the testicles make this possible. Sertoli cells act as support scaffolding: they surround developing sperm, nourish them, and guide their maturation. In the final stages, round immature cells are reshaped into the familiar elongated form with a tail, then released from the Sertoli cells and flushed into the epididymis by fluid flow. Leydig cells, located between the sperm-producing tubes, are responsible for manufacturing testosterone, which is absolutely required for spermatogenesis to proceed.
Hormones That Run the System
The entire male reproductive system is controlled by a hormonal chain of command that starts in the brain. A region called the hypothalamus releases a signaling hormone in pulses, and those pulses tell the pituitary gland (a pea-sized gland at the base of the brain) to produce two key hormones: luteinizing hormone (LH) and follicle-stimulating hormone (FSH).
LH travels through the bloodstream to the testicles and tells Leydig cells to produce testosterone. FSH targets the Sertoli cells and stimulates sperm production, including boosting the early-stage division of sperm precursor cells. The system includes a built-in feedback loop: when testosterone levels rise high enough, the brain scales back its signaling, which reduces LH and FSH output. When testosterone drops, the brain ramps signaling back up. This keeps hormone levels relatively stable day to day.
Testosterone does far more than support reproduction. It drives the development of muscle mass and strength, influences where the body stores fat, maintains bone density, and regulates sex drive. It’s also responsible for the physical changes of male puberty, including voice deepening, facial hair growth, and genital development.
What Semen Actually Contains
Semen is not mostly sperm. Sperm cells make up only a small fraction of the total volume. The bulk of semen is a cocktail of fluids from the accessory glands, each designed to keep sperm alive and moving. The fructose from the seminal vesicles fuels sperm like a sugar solution. The alkaline secretions from the prostate and bulbourethral glands counteract acidic environments that would otherwise kill sperm quickly. Proteins in seminal fluid cause semen to briefly thicken after ejaculation, which may help keep it in place, before it gradually liquefies over several minutes.
How the System Changes With Age
The male reproductive system doesn’t shut down abruptly the way the female system does at menopause, but it does change gradually. Testosterone production typically starts declining around age 20, dropping an average of 1 to 2% per year. For most men, this slow decrease doesn’t cause noticeable symptoms for decades, but the cumulative effect over a lifetime can be significant.
Beyond the hormonal shift, several physical changes emerge over time. Blood flow to the penis decreases, and penile sensitivity drops. Erections become less frequent, less firm, and shorter in duration. The volume of fluid released during ejaculation decreases, and the refractory period (the time needed before another erection is possible after orgasm) gets longer. Some older men experience orgasm without ejaculation. None of these changes follow a fixed timeline. They vary widely from person to person and are influenced by overall health, cardiovascular fitness, and other factors.
Sperm production continues well into old age for most men, though sperm quality (including DNA integrity and motility) tends to decline gradually. This is one reason fertility specialists consider paternal age a relevant factor, even though men don’t have a hard biological cutoff for reproduction the way women do.