In this topic you will learn how the reproductive system functions.

Reproduction means "producing another member of the same species." In humans the body gets ready for this process at puberty. Puberty usually begins before a person reaches the age of 14.

The testes are the male reproductive organs, located in a sac between the legs called a scrotum. When testes develop during puberty, they produce hormones. One of them, testosterone, causes hair to grow on the face and body, skeletal muscles to grow, and the voice to deepen. The testes begin to produce sperm. Sperm can move through a tube called the urethra.

The ovaries are the female reproductive organs. They produce hormones during puberty. One hormone, estrogen, causes breasts to develop, hips to widen, and hair to appear on the legs and arms. The ovaries start to release eggs at puberty—one developed egg is released about once every 28 days. The egg moves to the oviduct. Fertilization can take place in the oviduct. Fertilization is the joining of a sperm and an egg into one cell.

In humans, an egg is fertilized by a sperm that enters the female body. Only one sperm is needed to fertilize an egg. The fertilized egg is called a zygote. The zygote travels down the oviduct and becomes attached to the walls of the uterus—a muscular organ where a baby develops. Its lining has thickened with blood and tissues in time to receive the zygote.

If the egg is not fertilized, the lining of the uterus breaks down. The lining and the unfertilized egg leave the female's body during a time called menstruation. This material leaves the body through an organ called the vagina. Menstruation occurs about two weeks after an egg is released from the ovary. It takes place about every 28 days. If the egg is fertilized, menstruation stops.

The zygote divides while it travels through the oviduct and continues to divide in the uterus. The rapidly dividing cells become a developing organism, or embryo. The embryo burrows into the thickened lining of the uterus, and the woman is said to be pregnant. Pregnancy in humans lasts about 280 days. No eggs are released during pregnancy.

During pregnancy, a developing baby receives food and oxygen from its mother through a tissue called the placenta. The baby is connected to the placenta by a rope-like structure called the umbilical cord. A fluid-filled sac, called an amnion, surrounds the baby for protection. By the end of the third month of pregnancy, all the organ systems are present and the embryo is called a fetus. About 9 months after fertilization the baby is ready to be born.