This information is about the parts of your body that are involved in sex and sexual response.

The penis

The outside of the penis is partly covered by the foreskin, unless it has been removed (circumcision). At the very top of the penis is a slit that opens to the urethra. This is a tube that carries urine and semen through the penis.

Two cylinders of spongy tissue (the corpus cavernosa) run the length of the inside of the penis. When a man becomes sexually excited, blood flows into these, making the penis stiff and erect.

The testicles and sperm

At the base of the penis is the scrotum. This is a bag of wrinkly skin that contains two testicles. The testicles make the hormone testosterone, which is important for sex drive. They also make sperm. Just before orgasm, sperm leaves the testicles through two long tubes. These are called the spermatic cords. They carry sperm to the ejaculatory duct inside the prostate gland.

The prostate gland and seminal vesicles

Sperm mixes with different fluids to form semen. These fluids are made in:

• the prostate gland, which is just under the bladder
• the seminal vesicles, which are two pouches between the bladder and the rectum.

They are joined by tubes to the ejaculatory duct in the prostate gland.

During orgasm the prostate contracts, pushing semen out of the penis. This is called ejaculation. The contractions help create the intense sensations felt during orgasm.

Erogenous zones

These are sensitive areas of the body. When touched or stimulated, they may produce sexual arousal.

Your penis, testicles, prostate and anus are erogenous zones. Your chest and nipples can also be sensitive. You may have other erogenous zones on your body that respond to touch. The sensitivity of these areas varies from man to man.

Hormones are substances that occur naturally in the body. They influence the growth and activity of cells.

The main sex hormone in men, testosterone, is made in the testicles. Testosterone helps make sperm and influences sex drive. Men also make a small amount of the female sex hormone oestrogen, which helps sperm production and maintains sex drive.

Changes in the level of sex hormones in your body can cause some physical symptoms that can affect your sexuality. These include:

• reduced sex drive
• erection difficulties
• tenderness in the breast tissue behind the nipples
• tiredness.

There are four possible stages of sexual response.

• Arousal or excitement is the awakening of sexual feelings. It is when you feel ‘turned on’ and ready for sex. You may feel aroused by thinking about sex, seeing someone you are attracted to, touching someone or being touched by someone. During arousal, your brain sends signals to nerves close to your penis. The nerves increase the blood flow to your penis and it becomes erect. Arousal may or may not lead to orgasm.
• Plateau is the phase where your body maintains a heightened state of arousal. Your body is very sensitive during this phase.
• Orgasm is the sexual climax. This is the feeling of intense pleasure that happens as areas of your body go into a series of regular contractions. You will ejaculate semen from your penis.
• Resolution is the phase that comes after sexual arousal and orgasm. This is when the sexual changes in the body go back to normal. Men cannot usually be sexually excited again for a while. How long this lasts depends on the age of the man. In young men, it may only last for a few minutes. In older men it may last for hours or even days.