The gonads are the end organs of reproduction, represented by the ovary in females and the testis in males. They produce and release germ cells, central to the survival of the species. Ovaries contain all the oocytes they will ever have at birth, although they will not begin to be released until puberty. The testis can produce sperm from the age of puberty until death. In addition to the formation of germ cells, testes and ovaries produce sex hormones that affect the physiology of many, if not all, nonreproductive organs. The steroid hormone-producing cells of the ovary are the theca and granulosa cells of the ovarian follicle; those of the testis are the Sertoli and Leydig cells. The function of the gonads is mainly regulated by the hypothalamic–pituitary axis. The human breast is a secondary reproductive organ that serves to feed the infant in the first months to years of life.