The Female Reproductive System

1. The Female Reproductive System Chapter 20 Part II

2. The Female Reproductive System

3. Female Reproductive System • Ovaries contain large number of follicles • produce female gametes (eggs or ova) in ovarian cycle • Fimbriae – extensions of fallopian tubes • partially cover each ovary • Its cilia draw in ovulated eggs • Uterus – 3 layers: • Perimetrium – outer layer of connective tissue • Myometrium – middle layer of smooth muscle • Endometrium – hormonally-responsive inner epithelial layer • shed during menstruation • Cervix – between the uterus and vagina

4. The Female Reproductive System

5. Organs of the Female Reproductive System • Ovaries – female gonads • Accessory sex organs: Vagina, uterus, and uterine tube • Vaginal opening posterior to urethra, both covered by labia minoraand majora • Erectile organ: clitoris, anterior margin of labia minora

6. Production of Oocytes • From the yolk sac germ cells migrate into ovaries • 5 months gestation, ovaries contain 6-7 million oogonia • Production of oogonia then ceases forever • Toward end of gestation, oogonia now primaryoocytes begin meiosis I • arrest in prophase I • Loss of primary ocytes continues throughout life: • At birth 2 million left • At puberty 400,000 • 400 oocytes are ovulated during reproductive years • rest undergo apoptosis

7. Follicles at Different Stages of Development

8. Follicles at Different Stages of Development • Primary oocytes are contained in primaryfollicles • oocyte + follicle cells • In response to FSH some follicles will enter ovarian cycle • and grow, producing layers of granulosa cells • Some primary follicles continue developing vesicles • and becoming secondaryfollicles • One follicle continues growth • Vesicles fuse, forming fluid-filled cavity called an antrum • Graafian follicle

9. Ovarian Cycle • As graafian follicle develops, primary oocyte completes meiosis I • One daughter cell (secondaryoocyte) receives cytoplasm • Other daughter, now a small polar bodydegenerates • Secondaryoocytearrests at metaphase II • Only fertilized ova complete meiosis II

10. Ovarian Cycle • Secondary oocyte is part of the graafian follicle • Granulosa cells form a layer around outside of follicle • Oocyte sits on a mound of this layer the cumulus oophorus • Corona radiata – ring of granulosa cells enclosing the secondary oocyte • Zona pellucida – gelatinous layer between oocyte and radiata • forms barrier to sperm penetration

11. Ovulation • 10-14 days after start of menstruation • Only 1 follicle survives • Others become atreticfollicles (degenerate) • Surviving graafian follicle forms bulge on surface of ovary • Secretes increasing levels of Estrogen • Graffian follicle releases secondary oocyte • Into uterine tube at ovulation

12. Ovulation From a Human Ovary

13. Fertilization • If a sperm passes through the corona radiata and zona pellucida and • Enters the cytoplasm of the occyte now the • Oocyte completes meiosis II • With formation of another polar body • If not fertilized within 2 days secondary oocyte degenerates

14. Ovarian Cycle • Following ovulation empty follicle under the influence of LH becomes a corpus luteum • Which secretes progesterone and estradiol • Nonfertile cycle, becomes corpus albicans(non- functional remnant)

15. Pituitary-Ovarian Axis • Hormonal interactions between anterior pituitary and ovaries • Anterior pituitary secretes luteinizing hormone (LH) and follicle-stimulating hormone (FSH) • Both promote cyclic changes in the ovaries • Both are controlled by GnRH from hypothalamus • FSH secretion slightly greater during early phase of menstrual cycle • LH secretion greatly exceeds FSH secretion prior to ovulation • Not clearly understood but believed to result from negative feedback effects

16. Menstrual (Monthly) Cycle • Approximately month-long cycle of ovarian activity • Humans, apes, Old_world monkeys • Menstration – characterized by shedding of endometrial lining accompanied by bleeding • And sexual receptivity anytime throughout the cycle • Nonprimate female mammals have estrous cycles • no shedding of endometrium and receptivity is limited • estrous animals that bleed (dogs and cats) is due to high estrogen that accompanies receptive period

17. Menstrual Cycle • In humans is about 28 days • Day 1 is taken to be the first day of menstruation • Days 1 thru ovulation constitutes the follicular phase • Time from ovulation to menstruation is luteal phase • Endometrial changes are called: menstrual, proliferative, and secretory phases

18. Follicular Phase • Lasts from day 1 to ~13 • Dominated by growth and death of a cohort of primary follicles into secondary follicles • With one survivor becoming a graafian follicle • Which will undergo ovulation • As follicles grow granulosa cells secrete increasing amounts of estradiol • Reaching peak about day 12

19. Follicular Phase • Follicular growth and estradial secretion dependent on FSH • FSH and estradiol induce formation of FSH receptors in granulosa cells • Follicles increasingly sensitive to the same level of FSH • At same time – FSH and estradiol recruit LH receptors in graafian follicle

20. Follicular Phase • Rapidly rising estradiol secretion: • Hypothalamus increases pulses of GnRH • Anterior pituitary sensitivity to GnRH increases: • results in greater LH secretion • Positive feedback between Estrogen and anterior pituitary • Results in LH surge, peaks 16 hrs before ovulation • And causes ovulation

21. The Cycle of Ovulation and Menstruation

22. The Luteal Phase • After ovulation – LH causes empty follicle to become corpus luteum • which secretes Estrogen and Progesterone • Progesterone levels rise and peak about a week after ovulation • Development of new follicles and another ovulation inhibited by: • High progesterone and estrogen exert strong negative feedback on LH and FSH • Inhibin from corpus luteum further suppresses FSH

23. Luteal Phase • No fertilization • corpus luteum regresses • Estrogen and Progesterone levels decline • With menstruation and new cycle of follicle development 20-69

24. Cyclic Changes in the Endometrium • Driven by cyclic changes in estrogen and progesterone levels • Proliferative phase (menstration cycle) occurs during follicular phase – increased levels of estrogen • Stimulates growth of endometrial lining and development of spiral arteries • Causes cervical mucus to become thin and watery to allow sperm penetration

25. Cyclic Changes in the Endometrium • Secretory phaseoccurs during luteal phase – endometrium becomes ready for implantation • Progesterone stimulates development of uterine glands • Progesterone and Estrogen cause endometrium to become thick, vascular, and spongy • Progesterone causes cervical mucus to thicken and become sticky

26. Menstrual phaseresults from drop in Progesterone and Estrogen following Corpus Luteum degeneration • Low progesterone: constriction of spiral arteries • Blood flow stops followed by necrosis and sloughing of endometrium

27. Endocrine Control of the Ovarian Cycle

28. Factors Affecting Menstrual Cycle • Release of GnRH is regulated not only by hormonal feedback but also by input from higher brain centers • Olfactory system can send activity to hypothalamus in response to pheromones • Can cause the “dormitory effect” in which cycles of roommates become synchronized

29. Factors Affecting Menstrual Cycle • Limbic system input to the hypothalamus: • In times of stress can cause functional amenorrhea(cessation of menstruation) • Also occurs in very thin or athletic females with low body weight • May be related to reduced leptin secretion by small adipocytes

30. Contraceptive Methods • Oral contraceptivepills – synthetic estrogen and progesterone • Taken daily for 3 weeks after menstrual period • Mimic Corpus Luteum so that negative feedback inhibits ovulation • Placebo pills taken in 4th wk to permit menstruation

31. Rhythm Method • Involves daily measurement of oral basal body temperature (BT) upon awakening because: • Oovarian steroids cause BT changes • Declining Estrogen on day of LH surge causes a slight drop in BT • Rising Progesterone on day after LH peak causes elevated BT

32. Menopause • Cessation of ovarian activity and menstruation roughly ~50 years • Ovaries depleted of follicles produce no estrogen • LH and FSH are high because of no negative feedback • Lack of Estrogen from ovaries most responsible for: • Hot flashes, osteoporosis, and increased risk of atherosclerosis

33. Fertilization and Changes in the Oocyte

34. Fertilization, Pregnancy, and Parturition • Once fertilization has occurred, secondary oocyte completes meiosis • Then undergoes mitosis resulting in a structure called a blastocyst • Blastocyst secretes human chorionic gonadotropin (HCG) • Maintains corpus luteum of mother and prevents menstruation • Parturition (childbirth)– dependent upon strong contractions of the uterus, stimulated by oxytocin

35. Fertilization, Cleavage, and Formation of a Blastocyst

36. Fertilization • During intercourse a male ejaculates ~ 300 million sperm into vagina of the female • During their passage through the female reproductive tract, • 10% gain ability to fertilize an oocyte (capacitation) • In order to become capacitated the sperm must be in the female tract for at least 7 hours • Capacitated sperm are guided up to the uterine tube toward the oocyte by chemotaxis and thermotaxis

37. Fertilization • Normally occurs in the uterine tube • Acrosome – sperm’s large, enzyme filled vesicle (above the nucleus) • Interaction of sperm with the zonapellucida triggers an acrosomal reaction • stimulates fusion of acrosome with cell membrane • Within 12 hrs. after fertilization • nuclear membrane of ovum disappears and • ovum chromosomes joins the sperm chromosomes • Fertilized ovum now a zygote, 23 pairs of chromosomes

38. Fertilization and the Acrosome Reaction

39. Cleavage, Blastocyst, and Implantation • Cleavage– diploid zygote undergoes mitotic divisions • becomes a morula (ball of cells) and • then a blastocyst (hollow ball of cells) • Implantation of the blastocyst in the endometrium begins between the 5th and 7th day • Trophoblast cellsof the blastocyst secrete HCG • functions like LH and maintains mother’s corpus luteum for the first 10 weeks • provides fetal contribution to placenta

40. The Placenta • Placenta is formed from the trophoblast cells of the fetus and • the adjacent maternal tissue in the endometrium • Oxygen, nutrients, and wastes – exchanged by diffusion between the fetal and maternal blood • Umbilical cordcontains the fetal blood • carries it to and from the fetus and the placenta • Placenta secretes hormones: human chorionic somatomammotropin (hCS) and estradiol

41. Labor and Parturition • Contractions of the uterus – stimulated by oxytocin from the posterior pituitary and • by prostaglandins produced within the uterus • Androgens (primarily DHEAS) secreted by fetal adrenal cortex are converted into estrogen by the placenta • Estrogen secretion by the placenta induces oxytocin synthesis • enhances uterine sensitivity to oxytocin, and promotes prostaglandin synthesis in the uterus • Events culminate in labor and parturition

43. Lactation • Prolactin – secreted by anterior pituitary stimulates mammary glands to produce milk • Controlled by prolactin-inhibiting hormone (PIH) and stimulated by estrogen • High estrogen levels prepare mammary glands for lactation • But PIH prevents prolactin from stimulating milk production • After parturition declining levels of estrogen allow increase in secretion of prolactin

44. Milk production is prevented during pregnancy by estrogen stimulation of PIH

45. Milk production stimulated by prolactin • Milk ejection stimulated by oxytocin • Stimulus of sucking triggers a neuroendocrine milk-ejection reflex with an increased secretion of oxytocin and prolactin

46. Maternal Antibodies Protect the Baby

47. In Vitro Fertilization • Intracytoplasmic sperm injection (ICSI) • A single capacitated sperm is injected through the zona pellucida and into cytoplasm of a secondary oocyte • Grown in vitro for 3 days ( 8-cell stage) or 5 days (blastocyst) • Transferred to the woman’s uterus