(d) : Progesterone is secreted by the corpus luteum of the ovary. It stimulates further development of the uterine epithelium and mammary glands. It is also required for the formation of the placenta and for the maintenance of pregnancy. Luteotrophichormone and luteinizing hormone are secreted by the anterior lobe of pituitary gland. Estrogen is secreted by the cells of the Graafian follicles.