THE FEMALE MENSTRUAL CYCLE Biology 12 DEFINITIONS The

THE FEMALE MENSTRUAL CYCLE Biology 12

DEFINITIONS: The menstrual cycle is the term for the physiological changes that can occur in fertile women for the purposes of sexual reproduction and fertilization § The menstrual cycle is regulated by hormones. Menstruation is the shedding of the lining of the uterus (endometrium) accompanied by bleeding. § Menstruation starts during puberty and stops permanently at menopause § Does not occur during pregnancy

PARTS (WITHIN THE OVARY): Follicles: structures in the ovaries that contain the egg and secrete estrogen Corpus luteum: mass of follicle cells that form within the ovary after the egg is released, main function = producing estrogen and progesterone

THE MENSTRUAL CYCLE CAN BE DIVIDED INTO 4 PHASES: 1. 2. 3. 4. Flow Phase Follicular Phase Ovulation Luteal Phase

1. FLOW PHASE Marks the beginning of the cycle Characterized by the shedding of the endometrium. Lasts about 5 days Triggered by decreasing progesterone and estrogen levels

2. FOLLICULAR PHASE Started by an increase in FSH The follicle develops within the ovary § Follicle cells produce estrogen which promotes the thickening of the endometrium. Usually one follicle matures during each cycle Occurs approx during days 6 -13 of the cycle (lasts about 10 days)

INSIDE AN OVARY:

3. OVULATION Sharp increase in LH and small inc in FSH Around day 14 The oocyte bursts from follicle The remaining follicle cells become the corpus luteum

4. LUTEAL PHASE Development and maturation of corpus luteum occurs The corpus luteum begins secreting progesterone. § Progesterone § maintains the endometrium § strengthens the uterus § inhibits further ovulation § prevents uterine contractions If pregnancy does not occur, the conc of progesterone declines which triggers uterine contractions and the shedding of the endometrium

MENOPAUSE: Is the permanent stopping of the primary functions of the human ovaries § Due to a 90% decrease in estrogen The transition from reproductive to nonreproductive is the result of a reduction in female hormonal production by the ovaries

BIRTH CONTROL PILL: Birth control pills contain hormones that suppress ovulation. Without ovulation there is no egg to be fertilized and pregnancy cannot occur. There are 2 types of birth control pills § Combined pill (contains both estrogen and progesterone) § Mini pill (contains only progesterone)

TO DO: Video: § http: //www. youtube. com/watch? v=WGJsr. Gm. We. KE Complete Menstrual Cycle Graphing Complete Human Development WS