Progesterone is secreted by the cells of the corpus luteum. During the uterine cycle, it prepares the uterine endometrium for implantation. During the first trimester, progesterone maintains the uterine lining. Higher levels of progesterone inhibit the secretion of GnRH (gonadotropin-releasing hormone). This results in inhibition of the secretions of FSH and LH which in turn are required for the development of follicle and ovulation respectively.
Lower levels of progesterone during pregnancy results in sloughing off of uterine lining and the embryo during menstruation causing abortion.
One way in which classification is used at school is the separation of different subjects and subject materials. For instance one day you may go to a math class, while another day you may go to a french class.
