Girlology: A Girl's Guide to Stuff that Matters

hormone that causes boys to grow facial hair, pubic hair, larger muscles and thickened vocal cords that give them their deeper voice (after it goes through the squeaky phase while the voicebox is growing). Guys have two testes, and they often call them their “balls” or their “nuts.” They can be really tender and painful if hit or bumped hard. That’s why guys in sports have to wear a plastic guard called an athletic cup over their penis and testicles to protect those sensitive parts. Some guys in other sports may wear a jock strap, which holds the penis and testicles close to the body and keeps them from flopping and swinging too much. A jock strap keeps a guy’s privates comfortable and secure, like a jogging bra keeps our breasts snug and comfy during vigorous activity.Scrotum—the sac of skin that hold the testicles. It’s located behind the penis and between the legs. Did you know that sperm can only be made properly at a temperature that is slightly lower than our usual body temperature (in fact, they grow best at precisely 96.6 degrees Fahrenheit)? That’s why the scrotum hangs away from the body and keeps the testicles cooler, so they can do their thing. In really cold weather, the scrotum will pull closer into the body to keep the testicles at the right temperature. So guys kind of have this built-in incubator with its own thermometer . . . wow! But don’t believe for a minute that hanging out in a hot tub will kill a guy’s sperm and make it impossible to get pregnant!

Sperm—the little things that a male makes that fertilize a female’s egg. Sperm are so tiny that millions of them would fit into a teaspoon. You can’t see a sperm unless you look under a microscope. If you do that, they actually look like tiny tadpoles, and they swim! It takes about 90 days for a sperm to grow and mature in the male. When they come out of the penis, it is called ejaculation. For girls, only one egg is released each cycle, but for a guy, each time he ejaculates, he lets go of many millions of sperm. Some sperm will make girl babies, and some will make boy babies, so it’s up to the man’s sperm, not the woman’s egg, to determine whether a baby boy or baby girl will be made. (By the way, the plural form of sperm is sperm. So it’s one sperm, two sperm, five million sperm.)Epididymus—a very long, coiled-up tube on the outside surface of each testicle. It’s where the baby sperm spend a few weeks while they are growing into mature sperm . . . kind of like the incubator. When a male ejaculates, the sperm come from the epididymus, travel through some tubes and go out the opening at the end of the penis.Prostate and seminal vesicles—two glands that are inside a male that add fluid to the sperm so they have something to swim in and nutrition for the trip (have snacks, will travel!). Once the fluid is added to the sperm, the mixture is called semen.Semen—we just told you what this is, but we want to make sure you realize that semen is what comes out of the penis during sex or sexual excitement (the act is called ejaculation or “coming,” and the fluid itself is called semen, ejaculate or cum). When it comes out, it amounts to less than a tablespoon of liquid, but guess how many sperm are in it? MILLIONS!!! And it only takes ONE to fertilize an egg! When ejaculation happens, all those little sperm race to see which one can get to the egg first and make a baby. Talk about competitive!

Erection Section

If you are like most girls, erections seem like a really unusual phenomenon to you. For a girl, the closest thing that happens like that and can be noticeable to others is when you are wearing a thin shirt and your nipples get hard and poke out like headlights coming on! Sometimes embarrassing, sometimes not even noticeable. For guys, erections can be even worse.

Can you imagine something between your legs suddenly becoming hard, about twice its usual size and sticking up? That’s the embarrassing thing that happens to boys when they are in puberty and beyond. Boys can get erections even as babies. It happens sometimes if they have to pee or if they rub or play with their penises. In puberty, boys get “boners” a lot more frequently because of their hormones. Erections can be unpredictable and can happen at the worst times . . . like when a guy is asked to get up in front of the class to read a report. Yikes.

Erections usually happen if a guy is thinking about something sexy or having a fantasy. It will also happen if he is “playing with himself ” or masturbating. The embarrassing part for guys, though, is that sometimes they have no control over a sudden erection. It’s certainly not something you want to point out to them like, “Um, excuse me, is that a banana in your pocket or are you having an erection?”

Most of the time, guys find a way to hide it. They either won’t stand up, or they might put their hands in their pockets to hold themselves down. (“Down boy, down!”) Sometimes they will think about something unexciting (like kissing their grandmothers) to make erections go away. These erections usually last only a minute or so when they happen like that.

A teen guy will almost definitely get an erection if he is dancing closely, body to body, with his “sweetie” or if his crush sits on his lap. If you are the subject of one of these erections, don’t worry, it’s not your responsibility to help him make it go away. Some guys might expect you to “do something” sexual to help them “finish” their sexual excitement with an orgasm (read more about that in the next section). The great news here is that ALL guys know how to take care of that all by themselves. You should feel NO obligation, and don’t let any guy tell you differently!

The other thing you might hear about is a nocturnal emission— fondly known as a wet dream. A wet dream is when a guy ejaculates in his sleep. It might happen because of a sexy dream, or it might just happen for no reason. No need to ask your guy friends about it. They won’t want to talk about it, and some guys never have one.

The Journey of a Sperm

If you’ve been paying attention, we are sure you know that sex is how a baby is made, and we will definitely talk a lot more about sex stuff in this book. For now, let’s concentrate on getting this anatomy straight. It seems like a lot to learn, but it makes more sense when you understand how it all connects and works together. Let us take you on an amazing, swirly, twistyturny journey that will start with a sperm and end with a pregnancy happening in a female. Ready? Here we go.• Sperm are made in the testes. (You know that by now, right?)

• They travel into the epididymus (incubator), where they hang out for a few weeks until they grow and mature.

• With sexual excitement (we’ll get to that later), they are pushed through another tube called the vas deferens. In the vas deferens, they pass the seminal vesicles and prostate gland where they pick up their nutrients and fluids (snacks) and officially become semen.

• As the journey out continues, the sperm travel into the penis ,and with ejaculation, the semen squirts out of the penis through the urethra.

• If they come out during sexual intercourse, they find themselves in a woman’s vagina (hey, where are we? how’d we get here?). And they’re off, up the vagina, through the cervix, into the uterus, then into one of the fallopian tubes. Little do they know, there is usually only one egg. So that means about HALF of them will make a wrong turn down the empty fallopian tube (you know how men don’t like to ask for directions. . . .).

• Anyway . . . ahoy! After a long upstream swim, some (actually many many thousands) of the sperm finally reach the egg that has been floating peacefully down the fallopian tube since it ovulated. Eggs only live about 24 to 48 hours after ovulation, but sperm can live up to a week, so timing is important.

• They all surround the egg and start wiggling their way into it. Once one sperm gets through the egg’s wall, a special chemical is released that prevents any others from getting in. It’s like a lock down (or getting grounded!).

• The egg and sperm, now together, will share their genes (DNA or biological information that determines how a person looks, grows, etc.), and they begin to grow into a ball of cells that can eventually become a baby. The ball of cells (called an embryo) will then travel