The Menstrual Cycle. Model 1: Ovarian Cycle follicular cells

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1 The Menstrual Cycle REVIEW questions to complete before starting this POGIL activity 1. Gonads produce both gametes and sex steroid hormones. For the female, name the: A. gonads ovaries B. gametes oocyte/ovum/egg C. sex steroid hormones estrogen & progesterone The menstrual cycle includes cycles observed in the ovary, in plasma levels of reproductive hormones, and in the uterus. This activity looks at each of these cycles and the relationships among them. Model 1: Ovarian Cycle follicular cells oocytes 2. How many days are shown for this typical ovarian cycle? An ovarian follicle is an oocyte (developing egg) and its supporting or follicular cells in any stage of development, from immature to mature. Label the oocyte and the follicular cells in Model The ovarian cycle is subdivided into three phases. Complete the table below with information from Model 1. Ovarian Phase Name Days of Cycle Ovarian Events Follicular phase 1-13 Ovarian follicle develops Ovulation 14 Oocyte is released Luteal phase Corpus luteum forms then breaks down 5. When ovulation occurs, where does the oocyte go? Into the uterine tube

2 6. The corpus luteum is made from transformed cells. Where do these cells come from? Follicular cells remaining in the ovary after the mature follicle ruptures and releases the oocyte. 7. What happens to the corpus luteum near the end of the cycle? Predict the effect this has on its function. Corpus luteum regresses near the end of the cycle. It has a finite lifespan of days unless stimulated by HCG. As a result of the corpus luteum regressing, its function declines. Model 2: Ovarian Cycle + Plasma Levels of Sex Steroid Hormones 8. Name the two sex steroid hormones in Model 2. estrogen & progesterone 9. Name the ovarian phase(s) during which each hormone is secreted: Estrogen follicular & luteal phases Progesterone luteal phase 10. Predict the specific source(s) of each hormone: Estrogen follicular cells & corpus luteum Progesterone corpus luteum 11. Name the ovarian phase during which each hormone reaches its peak: Estrogen near the end of the follicular phase

3 Progesterone mid luteal phase 12. Plasma levels of both sex steroid hormones decrease near the end of the cycle. Predict the cause of this. Regression of the corpus luteum Model 3: Ovarian Cycle + Plasma Levels of Gonadotropins and Sex Steroid Hormones 13. The anterior pituitary secretes two gonadotropins. Name them, including both the abbreviated and long versions of their names. FSH = Follicle Stimulating Hormone LH = Luteinizing Hormone

4 14. What is the target tissue of these gonadotropins? ovaries 15. Plasma levels of gonadotropins peak on day 13. What ovarian event immediately follows the surge in LH? ovulation 16. Using your knowledge of the endocrine system and male hormones, complete this flow chart showing the relationship among female hormones, their sources, and their effects. Possible terms include: corpus luteum, estrogen, follicle cells, FSH, gametes/oocytes/ova, GnRH, LH, progesterone. GnRH FSH LH estrogen gametes corpus luteum 17. Progesterone exerts a negative feedback on LH and FSH release. A. In the flow chart above, draw in the arrow/line showing this negative feedback. B. Explain the meaning of negative feedback. Response lessens the stimulus 18. Estrogen is special in that it exerts both a negative and positive feedback on LH. The type of feedback depends on the concentration of estrogen. A. Explain the difference between negative feedback and positive feedback. Negative - response lessens the stimulus; important in homeostasis because it maintains variables within physiological ranges Positive response adds to the stimulus; used less often in homeostasis but is important in the menstrual cycle to stimulate ovulation.

5 B. Examine Model 3 to determine the feedback and circle the correct responses below. A small rise in estrogen levels (inhibits/stimulates) LH release; this shows (negative/positive) feedback on the anterior pituitary. High estrogen levels (inhibit/stimulate) LH release; this shows (negative/positive) feedback on the anterior pituitary. Model 4: Ovarian Cycle + Plasma Levels of Gonadotropins and Sex Steroid Hormones + Uterine Cycle

6 19. What part of the uterus is shown in Model 4? Which layer of the uterine wall is this? Endometrium the uterine lining 20. What event signals the start of the uterine cycle? Why do you think this event was chosen as the starting time? Onset of menstruation; it s the one event that is quite obvious and easily detected 21. The uterine cycle is subdivided into three phases. Fill in the information about these phases in the table below. Uterine Phase Name Days of Cycle Endometrial Events Menstruation 1-5 Shedding of the endometrium Proliferative phase 6-14 Rebuilding of the endometrium Secretory phase Endometrial glands and vasculature develop so that the lining becomes thicker 22. Each phase of the uterine cycle is associated with a phase of the ovarian cycle. Fillin the table below showing these associations. Days of Menstrual Ovarian Cycle Phase Uterine Cycle Phase Cycle 1-5 Follicular phase Menstruation 6-13 Follicular phase Proliferative phase 14 Ovulation Proliferative phase Luteal phase Secretory phase 23. Is the uterine cycle more directly influenced by gonadotropin or sex steroid levels? Explain. Sex steroids directly target the endometrium and affect is growth and development. 24. Describe the relationship between the elevated levels of progesterone during the luteal phase and the thickness of the endometrium days High levels of progesterone stimulate increased vasculature and glandular growth so the endometrium becomes thick, and ready for implantation. 25. What causes the decreased thickness of the endometrium near the end of the cycle? Regression of the corpus luteum decreased levels of estrogen & progesterone endometrium is no longer maintained menstruation will start soon.

7 Applications Questions: 26. What is menarche? What causes menarche? Menarche = first menstrual period. Changes in the hypothalamus occur increased GnRH increased gonadotropins secreted stimulation of the ovary beginning of a menstrual cycle. 27. What is menopause? What causes menopause? Menopause = no menstrual period for one year. The ovaries become refractory to the gonadotropins decreased secretion of estrogen and progesterone the endometrium no longer goes through the uterine cycle. 28. Why is it important for the endometrium to increase in thickness and vascularity during the menstrual cycle? Provides environment needed for implantation. 29. List three possible sources of reproductive failure (infertility) in females. Abnormal levels or cycling of gonadotropins and/or sex steroids Abnormal response of ovaries and/or endometrium to hormones Blockage of the uterine tubes 30. Predict changes that would occur in the uterine cycle if fertilization and implantation occur. (What are fertilization and implantation?) Fertilization = union of sperm and egg (secondary oocyte) Implantation = blastocyst settles into and interacts with endometrium; soon a placenta begins to develop. If fertilization and implantation occur, HCG is secreted corpus luteum is stimulated and does not regress estrogen & progesterone levels increase endometrium is maintained/grows thicker and menstruation does not occur. 31. If a woman has one ovary surgically removed, can she still become pregnant? Explain. She can still become pregnant because she has everything needed. 32. Considering Model 4, explain possible mechanisms of hormonal birth control methods. Combination pill contains estrogen & a progestin. If these steroid levels are maintained at a constant level, estrogen does not exert a positive feedback the LH surge does not occur ovulation does not occur (and follicles probably do not develop normally). Depo Provera is a progestin which exerts negative feedback and blocks typical ovarian cycles. 33. Do hormonal forms of birth control reduce one s chances of getting a STI/STD during sexual activity? Explain. No, they do not provide any mechanical barrier between the male and female genitals.