The ovary is an organ found in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary found on each side of the body. The ovaries also secrete hormones that play a role in the menstrual cycle and fertility. The ovary progresses through many stages beginning in the prenatal period through menopause. It is also an endocrine gland because of the various hormones that it secrete.  The ovary starts secreting more and more hormones at puberty. The hormones trigger the development of secondary sex traits. Starting with adolescence, the ovary undergoes structural and functional changes. The ability of the ovaries to control hormones makes them crucial to fertility and conception. A number of feedback mechanisms are stimulated when egg cells, or oocytes, are expelled from the Fallopian tube, which changes the hormone levels in the body.  Ovaries release progesterone, estrogen, testosterone, and inhibin at sexual maturity. The adrenal glands and ovaries in women create 50% of the body's testosterone, which is then immediately delivered into the bloodstream. Estrogen is in charge of the maturation and maintenance of the reproductive organs in their mature functional state, as well as the appearance of secondary sex characteristics in females during puberty. The uterus and mammary glands are prepared for pregnancy and breastfeeding, respectively, by progesterone. Progesterone and estrogen work together to promote endometrial changes associated with the menstrual cycle.