The prostate is a small gland in the male reproductive system whose main job is producing fluid that nourishes and transports sperm. About the size of a walnut and weighing around 25 grams in a healthy adult, it sits just below the bladder and wraps around the urethra, the tube that carries both urine and semen out of the body. That location is key to understanding both what the prostate does and why it causes problems as men age.
How the Prostate Supports Fertility
The prostate’s primary purpose is making a portion of the fluid that becomes semen. When you ejaculate, prostatic fluid mixes with sperm from the testicles and additional fluid from the seminal vesicles to form the final product. The prostate’s contribution contains enzymes, zinc, and citric acid, all of which help keep sperm alive and functioning after they leave the body.
One of the most important enzymes the prostate produces is PSA (prostate-specific antigen). Most people know PSA as something measured in a blood test, but its actual biological role is to liquefy semen after ejaculation. Semen initially forms a thick gel, and PSA breaks down the proteins responsible for that gel structure, freeing sperm to swim toward an egg. Other enzymes in prostatic fluid help sperm penetrate the protective barriers around an egg during fertilization.
The prostate is also partly muscular. During orgasm, those muscles contract to push semen into the urethra and propel it outward. So the gland works both as a fluid factory and as a pump.
Built-In Infection Defense
Beyond reproduction, the prostate plays a protective role that often gets overlooked. Prostatic fluid has strong antibacterial properties, largely thanks to its high zinc concentration. In healthy men, prostatic fluid contains an average of about 448 micrograms of zinc per milliliter. That zinc acts as a natural defense against bacteria that might otherwise travel up the urethra and infect the prostate, bladder, or kidneys.
Men with chronic bacterial prostatitis (a recurring prostate infection) tend to have dramatically lower zinc levels in their prostatic fluid, averaging around 50 micrograms per milliliter. That tenfold drop correlates with absent or severely reduced antibacterial activity, suggesting zinc is a frontline defense mechanism for the entire urinary tract.
What Drives Prostate Growth
The prostate depends on hormones to develop and function. Testosterone is the starting material, but the prostate itself converts about 10% of the body’s daily testosterone into a more potent form called DHT. This conversion happens directly inside prostate tissue, and it’s what drives the gland’s growth from puberty onward. Males born without the enzyme that makes this conversion possible typically have a very small or absent prostate, which confirms how central this hormone is to the gland’s existence.
During puberty, this hormone surge is what causes the prostate to reach its adult size. But the growth doesn’t stop permanently. Around age 25, the prostate enters a second, slower growth phase that continues for the rest of a man’s life. This is normal biology, not a disease, but it’s the reason the prostate becomes a source of trouble later on.
Why It Causes Problems With Age
Because the prostate wraps around the urethra, any enlargement squeezes the tube that carries urine from the bladder. This is benign prostatic hyperplasia, or BPH, and it’s extremely common. The growth tends to happen in the inner zone of the prostate, right where it presses against the urethra.
The numbers tell the story clearly. By age 40, the prostate may grow from walnut-sized to roughly the size of an apricot. By 60, it can reach the size of a lemon or tennis ball. BPH affects nearly half of men over 50 and up to 90% of men over 80. Symptoms include a weak urine stream, frequent urination (especially at night), difficulty starting or stopping urination, and the feeling that the bladder hasn’t fully emptied.
BPH is not prostate cancer, and having an enlarged prostate doesn’t increase your cancer risk. They’re separate conditions that happen to affect the same gland. However, the same hormonal environment that fuels normal prostate growth, particularly high local DHT production combined with certain genetic mutations, can also contribute to prostate cancer development. That’s why prostate screening becomes relevant as men get older.
A Gland That Does More Than You’d Think
For a walnut-sized organ, the prostate pulls considerable weight. It manufactures fluid that keeps sperm alive and mobile, produces enzymes that allow semen to function properly, contracts to physically propel semen during ejaculation, and secretes zinc-rich fluid that guards the urinary tract against infection. Its dependence on hormones means it never truly stops growing, which is why most men will eventually feel its effects on urination. Understanding what the prostate actually does makes it easier to understand why regular check-ups matter once you’re past 50, and why changes in urinary habits are worth paying attention to rather than brushing off as just getting older.