Reproductive system: overview

The reproductive system is different from the other systems you have studied: you can live without it, but a species cannot. Its job is to produce sex cells, called gametes, and to provide a place for a new human to develop. This lesson is a basic overview. Families and schools have different ways of discussing this topic, and you are encouraged to talk with a trusted adult or your health teacher about your questions.

Each gamete carries half of a parent's genetic information, 23 chromosomes. When a sperm cell and an egg cell join in fertilization, the new cell has the full 46, a unique mix from both parents.

In males, the testes produce sperm and the hormone testosterone. They hang outside the body in the scrotum, where it is slightly cooler than body temperature, which sperm need. Sperm mature in the epididymis and travel through the vas deferens. Glands add fluids to form semen, which exits through the urethra.

In females, the two ovaries contain egg cells and produce the hormones estrogen and progesterone. About once a month after puberty, an ovary releases an egg, which moves into a fallopian tube. If a sperm joins the egg there, fertilization happens. The uterus is a muscular organ whose lining thickens each month to prepare for a possible pregnancy. If no fertilized egg arrives, the lining is shed through the vagina in menstruation. This monthly cycle usually lasts between 21 and 35 days.

Puberty is the time when these organs mature. The hypothalamus and pituitary gland signal the testes or ovaries to make more hormones, as you learned in the endocrine lessons. Over a few years, the body grows quickly and changes. Puberty usually starts between ages 8 and 14, and its timing varies a great deal from person to person, which is normal.

After fertilization, the cell divides repeatedly and travels to the uterus, where it attaches to the lining. For the first eight weeks, the developing human is called an embryo, and after that a fetus. A pregnancy lasts about 40 weeks. A temporary organ, the placenta, lets the mother's blood and the baby's blood exchange oxygen, nutrients, and wastes without mixing.

Common mistake: thinking the male and female systems are unrelated. Both produce gametes and sex hormones controlled by the same pituitary signals. Next lesson: how all the systems work together.