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 minora and 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 primary
  oocytes 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 primary
  follicles
• 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 secondary follicles
• 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 (secondary oocyte) receives
  cytoplasm
• Other daughter, now a small polar body
  degenerates
• Secondary oocyte arrests 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 atretic follicles (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 phase occurs 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 phase results 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 contraceptive pills 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 sperms large, enzyme filled vesicle
  (above the nucleus)
• Interaction of sperm with the zona pellucida
  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 cells of the blastocyst secrete HCG
• functions like LH and maintains mothers 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 cord contains 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

42
(No Transcript)
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 womans uterus