Sex and Reproduction

The human body is amazing. It’s capable of running marathons, building skyscrapers, discovering cures for illnesses, and even inventing machines that can take people into outer space. Perhaps the most amazing thing the human body does is something we all take for granted—they can create other living human beings.

The next time you see a pregnant woman, consider just how incredible it is that people are capable of such a feat. Sex is a basic human function, and humankind could not exist without it. Although it might make you cringe to think about it, sex is how your parents made you. The first step is to understand your body, inside and out. Then you can get a handle on how sex and reproduction work.

Puberty Basics

Puberty is the period in a young person’s life when he or she becomes capable of sexual reproduction. Typically, girls start puberty between ages nine and fourteen, the average age being from ten to twelve years old. Boys go through puberty a bit later. Of course, the age when puberty begins varies, and you shouldn’t worry about your body’s schedule.

All kinds of changes take place before puberty happens. These changes signal the passage from childhood to adulthood, and mark the beginning of a very exciting, and oftentimes confusing, time in a person’s life.

Puberty can be bewildering or strange. For one thing, it may seem like your body changes overnight. Your whole body grows. Pimples may appear. Hair starts sprouting up under your arms and around your genitals. Boys might see some stray facial hairs, their voices will begin to deepen, and they may have their first wet dreams. Girls will begin to get their period, or menstruate, and develop breasts.

Brain Chemistry

All of these changes start in your brain 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. One of the pituitary gland’s jobs is to release secretions of gonadotropic hormones that affect most of the body’s basic functions. The gonadotropin-releasing hormones stimulate the pituitary gland to begin secreting the gonadotropic hormones, which act on the gonads, or sex glands—the ovaries in females and the testes in males.

Sex Hormones

The gonads begin to grow and secrete sex hormones. In males, sex hormones include testosterone and androsterone, which are called androgens. In females, 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. It also makes the hips grow wider and the breasts grow fuller. In females, the estrogen, progesterone, and gonadotropic hormones work together to regulate the menstrual cycle. Females will start to produce mature eggs, or ova (sex cells). Women are born with ova, but it’s during puberty that they mature and are released. When an ovum (or one egg) is released, it’s possible for you to become pregnant. You will start your menstrual cycle.


The technical term for getting your period is “menstruation.” Menstruation typically occurs once a month. Girls have hundreds of thousands of tiny eggs—or ova—in their ovaries. The ovaries are located near the uterus, the organ in which a fetus grows during pregnancy. During the menstrual cycle, some eggs begin to mature inside the ovaries. The surrounding cells release an estrogen hormone that tells the lining of the uterus to thicken with blood and cells so that it can prepare to receive a possible fertilized egg (a pregnancy). The increase in estrogen makes the pituitary gland release a hormone that travels to the ovaries and causes one of the mature eggs to be released. This is called ovulation. The egg moves through the fallopian tube (you have two of these, one for each ovary) on its way to the uterus. If the egg isn’t fertilized and there is no pregnancy, the blood and cells lining the uterus break down and are discharged through the vagina. This process is called menstruation, and it usually lasts from three to seven days. The entire menstrual cycle, which was just described, can take anywhere from twenty-one to thirty-five days, but on average takes twenty-eight days.

Premenstrual Syndrome

Premenstrual syndrome (PMS) is the name for a group of physical and emotional changes that some women go through before their menstrual period begins. The symptoms follow a pattern: they reappear at about the same time each month, and go away after your period has begun.

Physical changes caused by PMS include breast tenderness or swelling, bloating, weight gain, headache, fatigue, constipation, and increased or decreased appetite. Emotional changes include depression, irritability, anxiety, tension, mood swings, inability to concentrate, and change in sex drive. You don’t need to have all of these to have PMS, and the severity of symptoms can vary from month to month.

There is no cure for PMS, but there are ways to cope. To prevent swelling, bloating, or breast tenderness, steer clear of salt and caffeine two weeks before your period. Reducing caffeine (found in coffee, tea, colas, and chocolate) can also calm anxiety, insomnia, and irritability. If you feel depressed, talk to a close friend, family member, or counselor. Schedule time for energizing exercise, and get extra sleep.

Pregnancy Basics

When fertilization first takes place, the fertilized egg is smaller than the head of a pin.
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, a process called fertilization occurs. A fertilized egg then travels to the uterus and implants itself in the uterine lining. 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 embryo forms tissues that develop into organs. 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 ends when the woman gives birth to the baby.