The human reproductive system functions to produce and transport gametes (sperm and egg cells) for fertilization, and to provide a suitable environment for fetal development. In females, the ovaries produce and release eggs, which travel through the fallopian tubes and may be fertilized by sperm. The fertilized egg then implants in the uterus, where it develops into a fetus. In males, the testes produce and release sperm, which are transported through the vas deferens and mixed with other fluids to form semen. During sexual intercourse, semen is ejaculated from the penis into the female reproductive tract to fertilize an egg.