Hesperian Health Guides
The Reproductive System in People Who Can Cause Pregnancy
HealthWiki > Where Women Have No Doctor > Chapter 4: Our Reproductive Bodies > The Reproductive System in People Who Can Cause Pregnancy
People who can cause pregnancy do so by making and delivering sperm. Sperm travel from the testicles through a tube where they become part of a fluid called semen. Semen comes out of the penis during sex, especially at climax. Each drop of semen has thousands of sperm, which are too small to see without a microscope. If sperm enters the vagina of a person who can become pregnant, it can combine with an egg to cause pregnancy.
Penis: This tube-shaped organ is made of spongy tissue and contains the urethra. The penis fills with blood and becomes stiff when the person is sexually excited.
Testicles (balls): The testicles begin to make sperm during puberty, and this continues for the rest of the person’s life. The testicles also make testosterone, a hormone that causes many of the physical changes of puberty. A person with testicles usually has two.
Scrotum: The testicles sit inside the scrotum, a sack of skin and muscle that hangs under the penis.
Vas deferens: These tubes carry sperm, mixed in semen, to the penis. When the vas deferens are cut in a vasectomy, sperm can no longer leave the person’s body.
Bladder: The bladder is a hollow organ where urine collects as it is made by the kidneys.
Urethra: This tube carries semen out of the body when the person climaxes during sex. It also carries urine out of the body, from where it is stored in the bladder.