All living organisms must reproduce, or create offspring, to continue the species. In human beings, the reproductive system is made up of the organs that work together to make it possible to create offspring.
Human reproduction is described as sexual reproduction because it requires sex cells contributed by both a male and a female. By contrast, some simple organisms—such as the paramecium—can copy their own genetic material to create a new organism that is genetically identical. This process is called asexual reproduction.
Male reproductive system
Men and women have different reproductive organs. For men, the basic reproductive organs are the testes. The two oval-shaped testes are housed in a pouchlike structure called the scrotum, which sits at the base of the penis. The purpose of the testes is to produce sperm (short for spermatozoa), the male sex cell. Sperm are microscopic cells shaped like tadpoles, with long tails. The penis is the male organ for sexual intercourse. When it is stimulated, the penis becomes firm and releases semen, a mixture of sperm and other fluids, from its tip. This process of release is called ejaculation. This small amount of semen contains between 200 and 300 million sperm. In sexual reproduction, sperm must join with an egg from a female to produce an offspring.
In all animals with backbones, including humans, chemicals called hormones are necessary in sexual reproduction. Hormones stimulate sexual maturity and prompt mating behavior. The primary male hormone is called testosterone. It is produced by the testes.
Female reproductive system
The human female reproductive system is designed to develop eggs (the female sex cells), transport sperm to a mature egg, house a developing baby, and give birth. Basic reproductive organs for a woman include the ovaries, fallopian tubes, uterus, and vagina.
As in the male, hormones are required in females for reproduction. Estrogen and progesterone are the female hormones. They are produced mainly by the ovaries and by the placenta, an organ that develops in the uterus of pregnant women.
Inside the female body are two ovaries, each of which contains about 300,000 eggs. Through a process called ovulation, an egg is released from an ovary. This process takes place about once a month in a woman of childbearing age. The egg travels from the ovary through a structure called a fallopian tube to a muscular organ known as the uterus. If the egg is not fertilized by a sperm cell on its journey, it is expelled from the woman's body in a process known as menstruation.
The tube-shaped vagina acts as the female sex organ, as the path for eliminating fluids during menstruation, and as the birth canal through which the baby travels during childbirth. During sexual intercourse, a man ejaculates semen into the female's vagina. From there the sperm swim up through the uterus to the fallopian tube. If an egg is present in the fallopian tube, a single sperm may join with it to create the basis of a new human life. This act is known as fertilization.
A fertilized egg moves into the uterus, where it may become embedded into the uterine wall. Although normally about 3 inches (7.5 centimeters) long and 2 inches (5 centimeters) wide, the uterus is capable of expanding considerably as a baby grows during pregnancy.
After approximately nine months of development, a baby is ready to leave a women's body. The neck of the uterus, known as the cervix, expands to create a wide opening into the vagina. Contractions of the uterus push the baby downward so that the baby may come out through the vagina.