About Guys

Get the scoop about how your body works, how it changes during puberty, and how it all comes together to make a baby.

Guide to male anatomy

Outside of your body

The penis has 2 parts: the glans (or head) and the shaft.

The urinary opening is an opening at the tip of penis. This is where pee leaves the body. It is also where cum leaves the body.

The scrotum is a loose bag of skin behind the penis. The scrotum contains two testicles. Testicles are often called balls.

Pubic hair is hair that grows around the sex organs.

The anus is the opening where feces (poop) leave the body.

Foreskin is a fold of skin that covers the head of the penis. All boys are born with foreskin, but many have been circumcised. Circumcision is an operation where the doctor cuts away the foreskin. Circumcisions are usually done when a baby is a few days old. If you are not circumcised, you should pull back the foreskin to clean underneath.

Inside of your body

Testicles make and store sperm. Testicles are egg-shaped.

The urethra is a tube. The urethra has 2 purposes.
1) When you come (ejaculate), sperm and seminal fluid travel through the urethra and out of end of your penis.
2) When you pee, urine goes from the bladder through the urethra and out the opening at the end of your penis.

Sperm are the male sex cells. A sperm and egg join to form a fetus. The fetus becomes a baby.

Semen is the fluid that contains sperm. Cum is slang for semen.

Reproduction: how babies are made

You might want to check out "Guide to Female Anatomy" before you read about reproduction.

The basics
Here is the short version of how a baby is made. First of all, a man and a woman have vaginal sex - this means that he puts his penis in her vagina. During sex, the man releases sperm from his penis into her vagina. The sperm swim deep into her body. If the sperm joins a woman's egg, a fetus will begin to develop. The fetus grows in her body for about 40 weeks.

The details
When a sperm and egg meet and join, a fetus can begin to grow. Before that can happen, sperm and eggs need to be made.

A man makes sperm in his testicles every day. When a man comes (ejaculates), sperm and other fluids spurt out of the end of his penis. The sperm and fluid is called cum (or semen.)

Once a month, a woman releases an egg from one of her ovaries - this is called ovulation. This egg moves through the fallopian tube toward the uterus.

When a man and woman have vaginal sex (penis in vagina), the man comes and releases sperm into her vagina. Then sperm swim up the woman's vagina, into her cervix, through her uterus, and into her fallopian tube. If the egg is in the fallopian tube, there is a good chance that the sperm and egg will meet and join. This is called fertilization.

The fertilized egg then needs a place to grow. The woman's uterus changes during the month. At certain times, the uterus is able to house the egg. If the uterus is ready, the egg attaches to the wall of the uterus and grows into a fetus over the next 40 weeks.

If the uterus is not ready, the fertilized egg leaves the woman's body when she has her period.

What is an erection?

When a man gets sexually aroused, his penis fills with blood. This causes the penis to grow larger, get stiff, and stand out from the man's body. This is called an erection, (or hard-on or boner). The penis does not have a bone in it. It is just made of spongy tissue that fills up with blood.

You can get an erection if you masturbate or have sex with someone. Erections can also happen anywhere or anytime. You might get an erection because you are thinking about sex, or maybe you are nervous or excited. Many men get erections in their sleep. It's also possible to get an erection for no reason at all.

Men have erections throughout their lives, even when they are babies. When a boy hits puberty, erections happen more often.

So what is an orgasm? What does it mean to ejaculate?

Once you are hard, you might come (or ejaculate). The muscles in the penis contract and force the sperm and other fluids to come out of the penis. It is hard to describe, and many people experience it differently. It basically feels very good and relaxing.

Women also have orgasms. Women do not ejaculate sperm like men do. However, a few women do release fluids from their vagina when they have an orgasm.

Here are more details:

• It is possible to come without having an orgasm.
• When you come, only semen can come out, not urine. You cannot urinate or pee when you are hard.
• After you come, your penis will get soft and cannot get hard again for a while. This is called the refractory period.
• Cum (or semen) is about 97% seminal fluid and 3% sperm. Seminal fluid is mostly water.

Puberty for guys

Puberty is when a person's body changes and starts looking like an adult. Most boys start puberty when they are 10 or 12 years old, but some start sooner and some start later. Here are some of the changes that happen to boys:

• Their testicles get larger
• Their penis gets larger
• They grow taller and more muscular
• They grow facial hair
• They grow pubic hair (hair around the penis and scrotum)
• Their voice gets deeper and might "crack"
• They might have pimples
• They have wet dreams
• Their underarms start to sweat and develop an odor

Puberty can be an uncomfortable time in people's lives. Some people go through puberty early, and they feel uncomfortable with their new bodies. Other people go through puberty later, and they cannot wait till they go through puberty. Either way, everyone goes through puberty.

Wet dreams

When boys are going through puberty, they often have wet dreams. A wet dream is when you ejaculate or come in your sleep. The first time you have a wet dream, you might think that you wet the bed until you realize the fluid is white and creamy. Wet dreams are normal. You cannot stop yourself from having wet dreams.

Masturbation

Masturbation is when someone touches themselves for pleasure. Slang terms for masturbation are "jacking off" and "playing with yourself."

• Many boys and girls masturbate. (Many adults masturbate as well.)
• Masturbating cannot hurt you. It will not cause you to run out of sperm.
• How often boys masturbate varies. They might do it many times a day, or once a week, or never.

Does size matter?

Many men worry that their penis is too small. Soft (or flaccid) penises come in many sizes. Even though soft penises vary, most adult men are 4 to 6 inches long when they are hard. A smaller penis just grows more when it gets hard than a larger penis grows.

The size of your penis can also change even when it's soft. It might get smaller when you get cold or nervous.

There are many myths about penis size. See how many you know.

Scrotum (balls)

• It's normal for one testicle to hang lower than the other. It's also possible for one to be larger than the other.
• Sperm are made at a lower temperature than your body. Your scrotum hang outside your body to keep the sperm the right temperature. If you get hot, your testicles will hang lower to stay cool. If you get cold, your testicles will tighten and stay closer to your body to keep warm.
• If you feel any lumps in your testicles, go to your doctor or clinic.
• If your testicles ache or feel painful, go to your doctor or clinic.
• "Blue balls" are when your testicles ache. This happens if you have an erection for a long time without coming. "Blue balls" will go away and do not cause any damage.

All about sperm

Sperm are the male sex cells. Sperm are made in your testicles. You start making sperm during puberty. You will continue to make sperm for the rest of your life. A woman is the opposite. She is born with a set number of eggs and never makes any more.

Here are some more details:

• You can never run out of sperm, even if you masturbate a lot or have sex a lot.
• Sperm only live a few days, but you are constantly making new sperm.
• Sperm are very fragile. Only a few make it all the way to the woman's egg.

The hormone zone

Hormones are chemicals in our bodies. Hormones tell our bodies how to grow, how to behave, and how to work. Some hormones are called sex hormones and are needed for reproduction. The main hormone in males is testosterone. The main hormones in females are estrogen and progesterone. Men have a little bit of the female hormones, and women have a little bit of testosterone.

Testosterone helps men make sperm. Testosterone also causes men to grow facial hair and other puberty changes.

The female sex hormones control a woman's periods. Hormones also cause women to grow breasts and other puberty changes.