The prostate is a small gland in the male body, roughly the size of a walnut. It sits just below the bladder and surrounds the urethra, the tube that carries urine out of the body. The prostate’s main role is to make fluid that mixes with sperm to form semen. During ejaculation, the prostate pushes semen through the urethra. Because it wraps around the urethra, swelling or growth in the prostate can make urination more difficult. The prostate usually gets bigger as men age, and prostate cancer can develop in this gland.
Diagram of the prostate below the bladder and around the urethra, with notes on semen, ejaculation, age-related growth, and urine flow.