THE REPRODUCTIVE SYSTEM
The male and female reproductive systems are the only primary organs that differ between the genders.

Each reproductive system consists of gonads (ovaries in females and testes in males) and other associated structures.

Sex cells (sperm) are produced in males by the paired testes. Female organs that produce sex cells are the paired ovaries. In healthy women of reproductive age, one of the two ovaries releases a single sex cell, or ovum, approximately every 28 days. If the ovum is swept into one of the two oviducts to the uterus, and if it encounters a sperm, fertilization may occur. The resulting zygote, a single-celled organism, may then begin growth in the female's uterus, the site of embryo implantation and development.