The prostate

Prostate gland · prostata

A walnut-sized gland under the bladder in men that adds fluid to semen.

What it does

The prostate sits below the bladder and wraps around the urethra. It produces a milky fluid that makes up part of semen and helps sperm survive. Its muscle squeezes the fluid into the urethra during ejaculation.

Surprising fact

The prostate commonly grows larger with age, and because it surrounds the urethra, this can slow the flow of urine and make men get up at night to go.