Menstrual Cycle - Reproductive cycle of higher primates in which the ovary of the nonpregnant female develops an oocyte (egg) and prepares the uterine lining in case the egg is fertilized. Complete cycle averages 28 days in human females.

Endometrium - Thickened lining of the uterus during pregnancy.

Oocyte - Name of egg when it is produced by the follicle during the menstrual cycle.

Follicle - Microscopic structure in the ovary that contains the developing oocyte (egg) and secretes estrogen.

Corpus Luteum - A secreting tissue in the ovary that is formed of follicle cells after ovulation (release of oocyte). It produces progesterone to help stimulate thickening of the uterine lining prior to implantation.

Estrogen (Oestrogen) - Primary female sex hormone, produced in the ovary by the developing follicle (and in lesser amounts by the corpus luteum). It stimulates development and maintenance of the female reproductive system and secondary sex characteristics.

Progesterone - Hormone released by the corpus luteum which stimulates the preparation and maintenance of the uterine lining before the fertilized egg can implant. If implantation occurs, the corpus luteum continues to produce progesterone until immediately before birth to maintain the fetus.

LH - Luteinizing Hormone: Increases in LH causes ovulation (release of egg from follicle).

FSH - Follicle Stimulating Hormone: Increases in FSH stimulate development of a new follicle and increases estrogen secretion by the follicle.

Positive Feedback - (Example: increased FSH levels stimulate the increase in estrogen secretion by the follicle.)

Negative Feedback - (Example #1: increased LH levels cause the follicle cells to release less estrogen.) (Example #2: increased progesterone and estrogen both inhibit FSH and LH secretion.) (Example #3: increased FSH decreases progesterone secretion.)