Sex and Reproduction

The human body is an amazing thing. It’s capable of a wide range of activities, everything from competing in triathlons, building skyscrapers, and exploring outer space to deep meditation, constructing infinitesimally small microchips, and microscopic exploration of its own cells and genetic code. Human beings have discovered cures for deadly illnesses and have invented machines that have the ability to think like their creators, make decisions, and take the appropriate actions. But perhaps the most amazing thing humans can do is something that we often take for granted—we can create other living, breathing human beings.

Sex is a basic human function, and humankind could not continue to exist without it. And, although it might make you cringe to think about it, sex is how your parents made you. As a man, you should know what sex is all about. The first step is to understand your body, inside and out, and then you can get a handle on how sex and reproduction work.

Pregnancy Basics

Human beings, like most animals, reproduce sexually. A human baby is created when a female sex cell and a male sex cell unite. These sex cells are called gametes. Male gametes are called sperm; female gametes are called ova, or eggs. When a sperm and an egg are united, the fertilization process occurs. A fertilized egg grows into a baby inside a woman’s body. This is called pregnancy, and it lasts for approximately nine months.

When fertilization first takes place, the fertilized egg is smaller than the head of a pin. The fertilized egg grows into a group of cells called an embryo. The cells form tissues, and then organs develop. At this point, the embryo is called a fetus. During the rest of the pregnancy, the fetus continues to grow and develop. After about nine months, the fetus is fully developed and can live outside of the mother’s body. Pregnancy usually ends when the woman gives birth to the baby.

Puberty Basics

Puberty is the period between childhood and adulthood when guys and girls become sexually mature. This usually occurs in their early to mid-teens. Puberty is usually defined as the period in a young person’s life when they become capable of sexual reproduction. There are all kinds of changes that take place before this happens. These changes signal the passage from childhood to adulthood and mark the beginning of a very exciting time in a person’s life. However, just because somebody is physically capable of becoming a father, it doesn’t mean that that person is emotionally capable of taking care of another human being.

Puberty can be a confusing time for guys. For one thing, it may seem like your body changes overnight. Your whole body grows (sometimes so quickly that you seem to grow out of clothes every few months). Pimples appear. Your genitals—the penis and testicles—begin to grow and change. Hair starts sprouting up under your arms and around your genitals. You’ll begin to develop facial hair, your voice will begin to get deeper, and you’ll have your first wet dream (when you ejaculate—or release semen—while sleeping).

Brain Chemistry

All these changes start in your brain. It all has to do with hormones—chemicals in your body that control everything that happens during puberty. When puberty begins, a part of the brain called the hypothalamus starts to release large amounts of the gonadotropin-releasing hormone. This hormone acts on the brain’s pituitary gland. The pituitary gland has the job of releasing secretions that affect most of the body’s basic functions. The pituitary gland is stimulated by the gonadotropin-releasing hormone and begins to secrete the gonadotropic hormones. These hormones act on the gonads, or sex glands, which are the ovaries in females and the testes in males.

Sex Hormones

The gonads begin to grow and start secreting what are called sex hormones. In males, these sex hormones include testosterone and androsterone, which are called androgens. In females, these sex hormones include progesterone and estrogen, which are called estrogens. Sex hormones regulate the changes that take place during puberty. They are responsible for a person’s growth and weight gain. They also tell your body when to stop growing.

In males, androgens make the sex organs grow and develop. They make the voice deepen and cause the growth of facial hair. In females, estrogen makes the sex organs grow and develop. In females, the estrogen, progesterone, and gonadotropic hormones work together to regulate the menstrual cycle.

When Puberty Hits

Boys generally start puberty about two years after girls do, the average age being from twelve to fourteen years old. From start to finish, puberty usually lasts five to six years for most boys. Of course, the age when puberty begins and how long it lasts vary from person to person and from culture to culture. Don’t worry if you haven’t seen any signs of puberty yet. It will happen to you eventually.

Physical Changes of Puberty

Once puberty starts, boys’ bodies start to change dramatically. By the time puberty is over, the typical adolescent is seventeen or eighteen years old, four to twelve inches (ten to thirty cm) taller, fifteen to sixty-five pounds (seven to twenty-nine kilograms) heavier, stronger and more coordinated, and able to reproduce. In order for this transformation from boyhood to manhood to happen, many changes must first take place.

Sex Organs Enlarge

The first noticeable change of puberty is that a boy’s sex organs get bigger. These are the parts of the body that make a man a man and enable men to reproduce. The sex organs are the penis and the testes. The testes, also called testicles, are located in the scrotum. The testes have two purposes. They produce sperm—the male sex cell—one of which will unite with a woman’s egg to form a baby. The testes’ second function is to produce testosterone, the hormone responsible for many of the male secondary sex characteristics (such as hair growth on the face, underarms, and genitals).

The first change the testosterone makes is in the testes themselves. The testes start to grow, and of course the scrotum has to enlarge, too, in order to accommodate them. Before puberty, the testes measure less than an inch (2.5 cm) in length. They are about the same size they have been since age one. Once puberty starts, they grow gradually over the next six or so years, until they are about 2 inches (5 cm) long.

As the testes grow, they produce more and more testosterone. A few months after the testes start to enlarge, you can see the effect of the higher hormone level on the penis. Since about age four, most boys’ penises are about 1.5 inches (4 cm) long. During puberty, they get bigger and longer. They keep growing for about two years. There is no standard size for an adult penis. The average is between 3 and 6 inches (8 and 15 cm). The size of the penis does not make a person more or less manly than someone else. Like noses and ears, big ones and small ones work equally well.

Penis Size

All boys wonder about the growth of their penis at some time or another. If you have not begun to see signs of puberty in your genital area, you may be wondering what to expect. You may wonder if your penis will ever grow any bigger. As with other developments during puberty, changes like those in the size of your body’s sexual organs happen on your own personal timetable. There is no need to worry unless you reach the age of eighteen and have not gone through any puberty changes.

You may be interested to learn that your genitals are one of the first parts of your body to begin changing. You will probably see changes in your testicles, scrotum, and penis before you begin to grow taller or grow facial hair. First, the testicles grow larger, and the skin of the scrotum darkens in color. Then, the penis grows longer, and after that it grows thicker. Even after a boy’s genitals grow during puberty, there is a difference in size from man to man. Most penises, however, are near the same size when they become erect.

Keep all this information in mind if you suspect that you are a late bloomer. If you need or want to speak with a doctor about your concerns, you can be sure that this is a discussion that is routine for them.

Wet Dreams

When the male reproductive system has reached maturity, the sex glands (testes) have started to produce testosterone. Testosterone is necessary for the maturing of sperm in the testicles. If you look at sperm under a microscope, they look like tadpoles, with round heads and little tails. During puberty, boys will often release semen—a thick, sticky fluid that contains sperm—in their sleep. These are called wet dreams or nocturnal emissions. When a guy has a wet dream, it means that he has ejaculated in his sleep. All guys have them, and they’re absolutely normal.

Getting Taller

Among the most dramatic changes of puberty are growth spurts. A spurt is a sudden surge, and you can grow very quickly during this period, as much as four inches (10 cm) in one year! The biggest spurt, when you grow the fastest, occurs about two years into puberty. Boys grow at a little slower rate than girls, but they grow for a longer period of time. That is why men are generally taller than women. By the time you are eighteen, you are about as tall as you will get. You will probably not grow more than three-quarters of an inch (2 cm) after that.

All of your bones do not get longer all at once. The first bones to grow are the ones in your hands and feet. You may outgrow several shoe sizes in one year! Next, the bones in your arms and legs get longer. Finally, the rest of your body grows. This uneven growth can make you feel awkward and clumsy. You might actually trip over your own feet because you are not used to them being so big. Just wait: everything else will eventually catch up.

Because you are growing so rapidly, you may experience growing pains. These are very deep aches, usually in the legs. Along with your bones, your muscles are growing and stretching. When you are very active—if you play a sport, for example—you put extra stress on muscles that are already stressed by the process of growing. Growing pains are normal, and they go away with time. In addition, about half of all boys feel some tenderness and swelling around their nipples during puberty. This, too, is normal. Like growing pains, it will go away with time.