Menstrual Cycle

Oviduct Ovaries Follicles Corpus luteum Uterine wall Uterus LE 46-9b Oviduct Ovaries Follicles Corpus luteum Uterine wall Uterus Endometrium Cervix Vagina

The Menstrual Cycle 4 phases Phase 1: Follicular Phase Phase 2: Ovulation Phase 3: Luteal Phase Phase 4: Menstruation

Menstrual Cycle Follicular Phase Ovulation Luteal Phase Menstruation Pituitary releases FSH, causing follicle to grow Follicle release estrogen helping the endometrium to grow Causing the pituitary to release LH Ovulation Excess LH causes follicle to burst, releasing the ovum during ovulation Luteal Phase Shed follicle becomes the corpus luteum, which produces progesterone Progesterone causes the endometrium to thicken Menstruation If fertilization does not occur after 2 weeks, the corpus luteum dies, leading to menstruation.

Phase 1: Follicular Phase Anterior Pituitary secretes FSH stimulates several follicles in the ovaries to grow Eventually, one of these follicles gains the lead and dominates the others, which soon stop growing During all of this time, the follicle is releasing estrogen Estrogen helps the uterine lining (endometrium) to grow and eventually causes the pituitary to release a very large amount of LH. The endometrium is preparing for the implantation of a fertilized cell.

Phase 2: Ovulation The sudden surge of LH (luteal surge) in response to the increase in estrogen triggers ovulation Ovulation is the release of the follicle from the ovary The Luteal surge makes the follicle burst and release the ovum. The ovum them begins its journey into the fallopian tube, which is also known as the oviduct.

Phase 3: Luteal Phase The ovum has moved into the fallopian tube and the follicle has been ruptured and left behind in the ovary. The ruptured follicle (now a fluid filled sac) condenses into a little yellow blob called the corpus luteum.

Phase 3: The Luteal Phase The corpus luteum continues to secrete estrogen and now begins to secrete another hormone, progesterone Progesterone promotes the growth of glands and blood vessels in the endometrium. Without progesterone, a fertilized ovum cannot latch onto the uterus and develop into an embryo. After about 13 to 15 days, if fertilization and implantation have not occurred, the corpus luteum shuts down. Once it has stopped producing estrogen and progesterone, the final phase of the menstrual cycle begins.

The Menstrual Cycle Ovulation The menstrual cycle is divided into four phases. Notice the changes in hormone levels in the blood, the development of the follicle, and the changes in the uterine lining during the menstrual cycle. Copyright Pearson Prentice Hall 9

Phase 4: Menstruation Once the corpus luteum turns off, the uterus can no longer maintain its thickened walls It starts to reabsorb most of the tissue that the progesterone encouraged it to grow Since too much to reabsorb, a certain amount is shed This sloughing off is known as menstruation or bleeding.

Copyright Pearson Prentice Hall

Menstrual Cycle Recap Follicular Phase Ovulation Luteal Phase Pituitary releases FSH, causing follicle to grow Follicle release estrogen helping the endometrium to grow Causing the pituitary to release LH Ovulation Excess LH causes follicle to burst, releasing the ovum during ovulation Luteal Phase Shed follicle becomes the corpus luteum, which produces progesterone Progesterone causes the endometrium to thicken Menstruation If fertilization does not occur after 2 weeks, the corpus luteum dies, leading to menstruation.

LE 46-13 Control by hypothalamus Inhibited by combination of estrogen and progesterone Hypothalamus Stimulated by high levels of estrogen GnRH Anterior pituitary Inhibited by low levels of estrogen FSH LH Pituitary gonadotropins in blood LH FSH FSH and LH stimulate follicle to grow LH surge triggers ovulation Ovarian cycle Corpus luteum Degenerating corpus luteum Growing follicle Mature follicle Follicular phase Ovulation Luteal phase Estrogen secreted by growing follicle in increasing amounts Progesterone and estrogen secreted by corpus luteum Ovarian hormones in blood Peak causes LH surge This figure shows how c. the ovarian cycle and E. the uterine(menstrual cycle) are regulated by changing hormone levels in the blood depicted in parts a. b. and d. The time scale at the bottom of the figure applies to parts b-e. Estrogen Progesterone Estrogen level very low Progesterone and estro- gen promote thickening of endometrium Uterine (menstrual) cycle Endometrium Menstrual flow phase Proliferative phase Secretory phase Days 5 10 14 15 20 25 28

Websites for Menstruation http://www.tutorvista.com/content/biology/biology-ii/reproduction/menstrual-cycle.php http://www.layyous.com/Videoclips/menstrual%20cycle.htm http://www.youtube.com/watch?v=pQ4QOQdnifk