How a man’s body works

Hormones

During and after the teen years, the testes (testicles) make a steady supply of hormones, mostly testosterone. Testosterone is the hormone that helps promote sex drive and erections. Men’s hormone levels vary, but most men have more testosterone than they need. A man with low testosterone may have trouble getting or keeping erections and may lose his desire for sex.

The testes also produce millions of sperm each day. Making mature sperm takes about 3 months. Part of this happens as the newly made sperm travel through a 20-foot long tube to ripen. This tube (called the epididymus) forms a coil that sits on top of each testicle.

Male orgasm

A man’s orgasm has 2 stages.

The first stage is called emission. A tube called the vas deferens takes sperm from the epididymus into the body toward the prostate gland. At the same time, fluids from the seminal vesicles are brought in. The fluids help nourish the sperm so they can live for some time after orgasm. The sperm are mixed with these fluids near the top end of the tube that comes out through the penis (the urethra). A small valve in the tube shuts to keep the semen from going up into the bladder. A man feels emission as “the point of no return,” when he knows he is about to have an orgasm.

The second stage of orgasm is ejaculation. During ejaculation the mixture of fluid and sperm, called semen, comes out of the tip of the penis. The drawing below shows the male sex organs.

Ejaculation is controlled by the same nerves that carry pleasure signals when the penis is touched. These nerves cause the muscles around the base of the penis to squeeze in rhythm. This pushes the semen out of the penis. At the same time, messages of pleasure are sent to the man’s brain. This is sometimes called the climax.