The female reproductive system's primary functions are to produce eggs, receive sperm for fertilization of eggs, grow and nourish a fetus, give birth, and provide offspring with nutrients. Secondary functions include regulation of growth and menstrual cycles.The external structures of the female reproductive system are called the genitals or genitalia. A labium (plural, labia) is a flap of skin that protects the clitoris, the vagina, and the opening of the urethra. The most external part of the reproductive system are two pairs of labia, the labia majora (outer lips) and the labia minora (inner lips). The clitoris is a small organ containing tightly packed nerves that provides stimulation during intercourse. The vagina, also called the birth canal, is the tract in the female reproductive system that extends from the opening on the outside of the body to the cervix. The vagina connects the genitals to the internal reproductive structures. It provides lubrication during intercourse, receives the penis, and conducts menstrual flow out of the body. The cervix is the narrow neck of the uterus whose mucus protects the uterus from foreign materials. The cervix also dilates during childbirth to allow passage of the baby. The uterus, also called the womb, is the organ where gestation occurs. Gestation is the process of human development from conception through birth. Extending off the uterus laterally are two fallopian tubes. A fallopian tube, also called a uterine tube, is a hollow tube between the ovary and the uterus that conducts eggs to the uterus during a woman's menstrual cycle. The portion of each tube closest to the nearby ovary is the site where fertilization normally occurs. The ovary is an organ that produces and releases eggs and estrogen and progesterone. A mammary gland is an exocrine gland that produces milk in response to hormones. The mammary glands are found on the chest (forming the physical structure of the breasts). This milk provides nutrients and immune support to offspring.