BIO 5 Ch 27 Female Reproductive System
follicle development
"Follicles progress from primordial, to primary, to secondary and tertiary/vesicular stages prior to ovulation—with the oocyte inside the follicle remaining as a primary oocyte until right before ovulation... The process of development from primordial to early tertiary follicle, takes ~ 2 months. Development of a small cohort of tertiary follicles, ending with ovulation of a secondary oocyte, occur over a course of approximately 28 days."-text
Negative then positive feedback loop for ovarian cycle
"The more granulosa and theca cells a follicle has (that is, the larger and more developed it is), the more estrogen it will produce in response to LH stimulation. As a result of these large follicles producing large amounts of estrogen, systemic plasma estrogen concentrations increase. The high concentrations of estrogen will stimulate the hypothalamus and pituitary to reduce the production of GnRH, LH, and FSH. Because the large tertiary follicles require FSH to grow and survive at this point, this decline in FSH caused by negative feedback leads most of them to die (atresia). Typically only one follicle, now called the dominant follicle, will survive this reduction in FSH. When only the one dominant follicle remains in the ovary, it again begins to secrete estrogen & produces more than all of the developing follicles did together before the negative feedback occurred! It produces so much estrogen that the normal negative feedback doesn't occur. Instead, these extremely high concentrations of estrogen trigger a regulatory switch in the anterior pituitary that responds by secreting large amounts of LH and FSH into the bloodstream. The positive feedback loop by which more estrogen triggers release of more LH and FSH only occurs at this point in the cycle. It is this large surge of LH that leads to ovulation... the surge also stimulates a change in the granulosa and theca cells that remain in the follicle after the oocyte has been ovulated → corpus luteum."
The Ovarian cycle (S6)
"The ovarian cycle is a set of predictable changes in a female's oocytes and ovarian follicles. During a woman's reproductive years, it is a roughly 28-day cycle that can be correlated with, but is not the same as, the menstrual cycle. The cycle includes two interrelated processes: oogenesis (the production of female gametes) and folliculogenesis (the growth and development of ovarian follicles)."-text Slides: "Ovarian cycle; monthly (~28 day) series of events associated with maturation of egg •Two consecutive phases, with ovulation occurring midcycle between [these two] phases: 1•Follicular phase = Phase of ovulatory cycle (day 1-14; varies) where the [vesicular] follicles in the ovary grow/mature. 2•Luteal phase: period of corpus luteum activity (days 14-28; doesn't vary/"is always 14 days from ovulation to end of cycle."). •Only 10-15% women have 28-day cycle."
24. What is blastocyst? (S36)
"hollow ball of cells after five days". •The blastocyst implants into the endometrial lining of the uterus by the end of the 1st week
23. What is morula?
"solid ball of cells after three days" First stage after fertilization. ~16 cells.
28. Pt 1 "Learn the major events that happen during the three major phases of human development" (S40-43): Pre-embryonic phase
1. Pre-embryonic phase (1st to 3rd weeks): Placenta develops during the 2nd week •Fetal portion of the placenta = blood vessels in chorionic sac •Maternal portion of the placenta = blood vessels in Decidula Basalis of endometrium •Mother and fetal blood vessels do not connect {[repeats below:]} •Differentiation of the inner cell mass into 3 types of germinal tissues; Ectoderm, Mesoderm, & Endoderm. •The 3rd week of development •Development of the Neural tube (CNS) •Secretion of Chorionic Gonadotropin hormone (CGH) that stimulates mother ovaries to secrete Progesterone through the pregnancy. (CGH is used for test for pregnancy)
28. Pt 2 "Learn the major events that happen during the three major phases of human development" Embryonic phase (S44-46)
2. Embryonic Phase 4th to 8th weeks The most critical period (if something goes wrong baby continues develop with serious deformities) 4th week: •Development of brain into 3 regions: forebrain, midbrain, and hindbrain •Development of the beating heart *Development of the respiratory system begins 8th week: •Digits of hand and feet •Further development of eyes, ears, nose •Bones begin to calcify •Development of the deciduous teeth
13. What is the average length of the menstrual cycle?
28 days. Note: "the length of the menstrual cycle varies among women, and even in the same woman from one cycle to the next, typically from 21 to 32 days." -text. Definition of menstrual cycle = the series of changes in which the uterine lining is shed, rebuilds, and prepares for implantation. The timing of the menstrual cycle starts with the first day of menses, referred to as day one of a woman's period. The three distinct phases of the menstrual cycle = the menses phase, the proliferative phase, and the secretory phase.
28. Pt 3 "Learn the major events that happen during the three major phases of human development" Fetal phase
3. Fetal Phase 9th week to birth 3rd month: •Sex can be determined •Eyelids are formed •Nail begin to develop •Kidney begin to producing urine *4th month (4.6 mo): fetal breathing movements may begin. 5th month: •Feel baby movement 6th month: •Pulmonary alveoli begin to develop/("by_wk_28, enough alveoli have matured that a baby born prematurely at this time can usually breathe on its own."Prior to wk 26 [6months]there's not enough surfactant yet so survival low:( 7th month: •Fetus rotates into cephalic presentation •Deposition of subcutaneous fat •Fetus capable of surviving *8th month: Surfactant levels are generally adequate/effective lung compliance. 8th, 9th months: •Baby becomes more "chubby" •Testes begin to descend into scrotum 10th month: •Post-term
Oogenesis (S1)
Begins in fetal period •Oogonia (2n ovarian stem cells[/diploid/46 chromosomes]) multiply by mitosis and store nutrients •Primary oocytes develop in primordial follicles that become surrounded by follicle cells -Primary oocytes begin meiosis but stall ["arrested"] in prophase I. -At birth, female presumed to have lifetime supply of primary oocytes. Primary oocytes = 1-2 million in an infant. approx 400,000 at puberty & 0 by the end of menopause.
17. What events occur during the secretory phase of the menstrual cycle?
Begins right after ovulation, "In the uterus, progesterone from the corpus luteum begins the secretory phase of the menstrual cycle, in which the endometrial lining prepares for implantation. Over the next 10 to 12 days, the endometrial glands secrete a fluid rich in glycogen. If fertilization has occurred, this fluid will nourish the ball of cells now developing from the zygote. At the same time, the spiral arteries develop to provide blood to the thickened stratum functionalis."-text +During the secretory phase of the menstrual cycle, progesterone reaches its highest levels. -High estrogen levels in this phase slightly decrease the acidity of the vagina. "IF no pregnancy occurs [during the secretory phase] within approximately 10 to 12 days, the corpus luteum will degrade into corpus albicans. Estrogen & progesterone levels will fall, and the endometrium will grow thinner. Prostaglandins will be secreted that cause constriction of the spiral arteries, & the endometrial tissue will die, resulting in menses—or the first day of the next cycle. #starting the 28day menstrual cycle all over again.
uterine (menstrual) cycle (S25-27)
Cyclic series of changes in endometrium that occur in response to fluctuating ovarian hormone levels [preparing it for arrival of fertilized ovum.] •Three phases of menstrual cycle: 1. Days 1-5: menstrual phase (menstruation/menses averages 5 days [can be 2-7 though]. 2. Days 6-14: proliferative (preovulatory) phase 3. Days 15-28: secretory (postovulatory) phase SO: 1. Days 1-5: menstrual phase Begins at day one with the start of menses. "Occurs during the early days of the follicular phase of the ovarian cycle, when progesterone, FSH, and LH levels are low. Since corpus luteum/progesterone degrades (marking the end of the luteal phase) this triggers the shedding of the stratum functionalis. •Stratum functionalis detaches from uterine wall and is shed -Menstrual flow of blood and tissue lasts 3-5 days •By day 5, growing ovarian follicles start to produce more estrogen [By day 5 of menstruation, the body knows, "ok, no pregnancy. So it's time to produce new oocyte, maybe this time pregnancy will happen".] 2. Days 6-14: proliferative (preovulatory) phase •Rising estrogen levels_(secreted by ovarian follicles) prompt generation of new stratum functionalis layer -As layer thickens, glands enlarge, and spiral arteries increase in number •Thins out normally thick, sticky cervical mucus to facilitate sperm passage •Ovulation occurs at end of proliferative phase on day 14, when the oocyte is released from the ovary & occurs once ~every 28 days. [see Q 19 for secretory phase/Days 15-28]
5. Learn the stages of follicle development (S7-11)
DETAILS: I. A primordial follicle becomes primary follicle 1. A single flat [squamouslike] layer of cells surrounding primary oocyte = primary oocyte. After puberty, a few primordial follicles will respond to a recruitment signal each day, and will join a pool of immature growing follicles called primary (1°) follicles. The granulosa cells then become active and transition from flat/squamous to cuboidal as they increase in size and proliferate. + the oocyte enlarges. •Process can take about one year 2.Follicle is now called primary (1°) follicle. II. Primary follicle becomes secondary follicle 3.Follicular cells proliferate, forming stratified epithelium around oocyte •When more than one layer of cells are present: -Follicular cells now called granulosa cells -Primary follicle called secondary follicle They continue to increase in diameter, adding a new outer layer of connective tissue, blood vessels, and theca cells—cells that work with the granulosa cells to produce estrogens.
16. What events occur during the proliferative phase of the menstrual cycle?
Days 6-14: proliferative (preovulatory) phase: •Rising estrogen levels_(secreted by ovarian follicles) prompt generation of new stratum functionalis layer -As layer thickens, glands enlarge, and spiral arteries increase in number •Thins out normally thick, sticky cervical mucus to facilitate sperm passage •Ovulation occurs at end of proliferative phase on day 14. "Once menstrual flow ceases, the endometrium begins to proliferate again, marking the beginning of the proliferative phase of the menstrual cycle. It occurs when the granulosa and theca cells of the tertiary follicles begin to produce increased amounts of estrogen. These rising estrogen concentrations stimulate the endometrial lining to rebuild."-text
25. What of are the three types of embryonic germinal tissues? (multiple Q's WILL be on test)
Differentiation of the inner cell mass into 3 types of germinal tissues: 1.Ectoderm 2.Mesoderm 3.Endoderm
19. What events occur during the secretory phase of the menses [menstrual cycle]? (S28)
Endometrial glands enlarge., the corpus luteum is formed, the fertilized ovum implants, progesterone levels are high. 3.Days 15-28: secretory (postovulatory) phase When endometrium prepares for embryo to implant •Rising progesterone levels from corpus luteum prompt: •Endometrial glands to enlarge and secrete nutrients into uterine cavity •Thickened mucus to form cervical mucus plug that blocks entry of more sperm, pathogens, or debris.
11. After ovulation, the ovary secretes ____________________________________________________ (S23)
Estrogen and progesterone. Note: Up til ovulation, body has almost NO progesterone, just rising estrogen. Shortly after ovulation: •Estrogen levels decline •LH transforms ruptured follicle into corpus luteum •LH stimulates corpus luteum to secrete progesterone and some estrogen almost immediately -Progesterone helps maintain stratum functionalis [of the uterus/promotes stratum to stay attached for a bit to 'see if get pregnant'] [AND progesterone inhibits secretion of GnRH]. -Maintains pregnancy, if it occurs. [NEED progesterone cuz if it drops, endometrium will shed off and won't be able to support embryo.]
20. Learn the effects of estrogens and progesterones on female development.(S32-33)
Estrogens: •Promote oogenesis and follicle growth in ovary •Exert anabolic effect on female reproductive tract •Induce secondary sex characteristics -Growth of breasts -Increased deposit of subcutaneous fat (hips and breasts) -Widening and lightening of pelvis Progesterone works with estrogen to establish and regulate uterine cycle •Promotes changes in cervical mucus •Effects of placental progesterone during pregnancy -Helps prepare breasts for lactation
4. What hormone is responsible for follicle maturation?
FSH (follicle-stimulating hormone). But also estrogens. Note: FSH stimulates sperm development by male testes. FSH & LH "leave the pituitary and travel to the ovaries, where they bind to receptors on the granulosa and theca cells of the follicles. FSH stimulates the follicles to grow (hence its name), and the five or six tertiary follicles expand in diameter. Note: The release of LH also stimulates the granulosa and theca cells of the follicles to produce the sex steroid hormone estradiol, a type of estrogen. This phase of the ovarian cycle, where the tertiary follicles are growing and secreting estrogen; is known as the follicular phase." -text
3. When is the second polar body produced?
Following meiosis II/when secondary oocyte finishes meiosis II (after fertilization), completing the oocyte's second round of division.
26. Learn the major structures and tissues developed from each germinal layer
From ectoderm [external layer] we develop skin cells/epidermis, neurons of brain, & pigment cells #ectoderm is epithelial cells; central and peripheral nervous systems, sensory organs, hair & nails." From mesoderm [middle layer], you form muscle cells & connective tissue cells. "skeleton, heart, blood vessels, and kidneys." Endoderm [internal layer]= epithelial cells too but they're the lining of digestive tract & endocrine glands +lining of lungs in alveoli. & also the lung, thyroid & digestive cells themselves. "endoderm goes on to form the epithelial lining of the gastrointestinal tract, liver, and pancreas, as well as the lungs". Note: Epithelial cells develop from all 3 layers.
1. What is oogenesis?
Gametogenesis in females is called oogenesis [it is the production, growth, and maturation of an ovum/egg]. The process begins with the ovarian stem cells, or oogonia, which form during fetal development, and divide via mitosis, much like spermatogonia in the testis. However, oogonia form primary oocytes [=primary spermatocytes for male] in the fetal ovary prior to birth [during puberty for male]. These primary oocytes are then arrested in this stage of meiosis I, only to resume it years later, beginning at puberty and continuing until the woman is near menopause. NOTE: (oocyte is activated 12 months before ovulation but matures about 14 days before ovulation) -Primary oocyte is 2n, secondary oocyte = 1n.
Hormonal Regulation of Ovarian Cycle (S18-22)
Hormonal interaction during ovarian cycle 1. GnRH stimulates FSH and LH secretion 2. FSH and LH stimulate follicles to grow, mature, and secrete sex hormones •FSH stimulates granulosa cells to release estrogen, and LH prods thecal cells to produce androgens, which granulosa converts to estrogens 3. Negative feedback inhibits gonadotropin release •Increasing levels of plasma estrogen levels exert negative feedback inhibition on FSH and LH release •Only dominant follicle can withstand this dip in FSH -Other developing follicles deteriorate 4. Positive feedback stimulates gonadotropin release •Estrogen levels continue to rise as a result of continued release by dominant follicle •When levels reach a critical high value, a brief positive feedback occurs on brain and anterior pituitary -Triggers LH surge 5. LH surge triggers ovulation and formation of the corpus luteum *Surge triggers ovulation •LH surge triggers primary oocyte to complete meiosis I to become secondary oocyte •Secondary oocyte then enters meiosis II, continuing on to metaphase II.
5. 1/2. Learn the stages of follicle development (part 2)
III. Secondary follicle becomes vesicular follicle •Connective tissue and granulosa cells condense to form theca folliculi. •Zona pellucida: thick, glycoprotein-rich membrane secreted by oocyte, encapsulating it. 4.Early vesicular follicle formed when clear fluid begins to accumulate between granulosa cells, called Antrum, forms large cavity. -Large, fully formed antrum distinguishes it as vesicular follicle [aka tertiary or antral follicle], no longer previous pre-antral follicle. (Note "several follicles reach the tertiary stage at the same time, but most will undergo atresia. The one that does not die will continue to grow and develop until ovulation.") •Antrum continues to expand with fluid isolating oocyte -Isolated oocyte with its surrounding granulosa cells called corona radiata •When follicle is full size (2.5 cm or 1 inch), it bulges from external ovary surface •It is ready to be ovulated.
6. What hormone trigger ovulation?
LH/Leutinizing hormone. The high estrogen concentration [originally secreted to rebuild endometrial lining/proliferation] will eventually lead to a decrease in FSH as a result of negative feedback, resulting in atresia [death of ovarian follicles] of all but one of the developing tertiary follicles. The switch to positive feedback—which occurs with the elevated estrogen production from the dominant follicle—then stimulates the LH surge that will trigger ovulation (the surge also triggers the resumption of meiosis in a primary oocyte, initiating the transition from primary to secondary oocyte). Ovulation marks the end of the proliferative phase AND the end of the follicular phase."-text Note: Only inside dominant follicle do we have secondary oocyte, inside all the other follicles, they're still primary oocytes.
comparison of chicken egg (S39)
Like in chicken egg, humans too have chorion [lining of embryo] and amnion. However, the allanois [sac for waste product] and yolk sac [nutrients] for humans is fused together forming the umbilical cord. Note: Placenta has 2 parts, the embryonic part and the maternal part.
15. Menstruation is triggered by a drop in the levels of _______________________________________ (S29)
Progesterone (from 'full' degeneration of corpus luteum/not secreting progesterone anymore cuz wasn't fertilized so it 'dies'). UTERINE (menstrual) cycle: If fertilization does not occur: •Corpus luteum degenerates; progesterone levels fall •Causes spiral arteries to kink and spasm. •Endometrial cells die, and glands regress. •Blood vessels fragment, and functional layer sloughs off. *Uterine cycle starts all over again on first day of menstruation.
9. What is the principal hormone secreted by the corpus luteum? (S16)
Progesterone. Luteal Phase of the Ovarian Cycle: •After ovulation, ruptured follicle collapses, and antrum fills with clotted blood -Referred to as corpus hemorrhagicum; will eventually be absorbed •Remaining granulosa cells and internal thecal cells enlarge to form corpus luteum •Corpus luteum secretes progesterone and some estrogen[at this phase though, estrogen level drops cuz we don't have follicle anymore to secrete estrogen, it's corpus luteum now]
Where does fertilization occur?
Sperm typically meet the egg while it is still moving through the ampulla (in uterine/fallopian tubes).
7. How can at-home kit be used to help predict when ovulation occurs?
Test by detecting a rise in luteinizing hormone (LH) in the urine. Just before ovulation there's a surge in LH hormone to signal the ovary to release the egg.
2. When does the second meiotic division in oogenesis occur? (S3-4)
When the ovum has been fertilized. •Secondary oocyte [ENTERS meiosis II but cannot finish it unless fertilized so#]arrests in metaphase II and becomes the ovulated ovum [/eventually leaves the ovary during ovulation]. •If penetrated by sperm, second oocyte completes meiosis II, yielding: - Ovum (functional gamete) - Second polar body [all polar bodies degenerate. they are simply the result of unequal cell division] "Meiosis of a secondary oocyte is completed only if a sperm succeeds in penetrating its barriers. Meiosis II then resumes, producing one haploid ovum that, at the instant of fertilization by a (haploid) sperm, becomes the first diploid cell of the new offspring (a zygote). Thus, the ovum can be thought of as a brief, transitional, haploid stage between the diploid oocyte and diploid zygote."-text
14. At which days in the 28-day cycle is a woman MOST likely to get pregnant?
day 14. "In a typical 28-day menstrual cycle, ovulation occurs on day 14."-text. /at the end of proliferative phase, when uterus is ready.
8. When does ovulation occur? (S 15)
ovulation typically occurs about 14 days before the start of the next menstrual period. After follicular phase causes follicle to reach its full size & bulge: •Rising levels of LH cause ovary wall to rupture, expelling secondary oocyte with its corona radiata to peritoneal cavity Note: "It is this large surge of LH that leads to ovulation of the dominant follicle. The LH surge induces many changes in the dominant follicle, including stimulating the resumption of meiosis of the primary oocyte to a secondary oocyte. The LH surge also triggers proteases (enzymes that cleave proteins) to break down structural proteins in the ovary wall on the surface of the bulging dominant follicle. This degradation of the wall, combined with pressure from the large, fluid-filled antrum, results in the expulsion of the oocyte surrounded by granulosa cells into the peritoneal cavity. This release is ovulation." -text
18. High level of progesterone, relatively high levels of inhibin, and low levels of FSH and LH is most likely representing ___________________________________ of the uterine cycle
the secretory phase.
12. Following ovulation, rising levels of estrogen stimulate the endometrium ___________________________________________________
to continue to proliferate. Note repeat:"Once menstrual flow ceases, the endometrium begins to proliferate again, marking the beginning of the proliferative phase of the menstrual cycle. It occurs when the granulosa and theca cells of the tertiary follicles begin to produce increased amounts of estrogen. These rising estrogen concentrations stimulate the endometrial lining to rebuild."-text
How twins are made
•1-2% of ovulations release more than one secondary oocyte, which, if fertilized, result in fraternal twins •Identical twins result from fertilization of one oocyte, then separation of daughter cells
Hormonal Regulation of Ovarian Cycle (pt 2, S24) If no fertilization occurs:
•Corpus luteum degenerates when LH levels start to fall •Causes a sharp decrease in estrogen and progesterone, which in turn ends blockage of FSH and LH secretion, causing cycle to start all over again *Oocyte is actually activated 12 months prior to ovulation but matures 14 days before ovulation.
follicular phase of ovarian cycle (S12-13)
•During follicular phase, several vesicular (antral) follicles are stimulated to grow •Triggered by rising levels of FSH •FSH levels drop around middle of follicular phase •Causes only one antral follicle, dominant follicle, to be selected to continue on {[(destroys all the other follicles)]} •How dominant follicle is chosen is still uncertain •Primary oocyte of dominant follicle completes meiosis I to form 2° [secondary] oocyte and polar body •Granulosa cells then send signal to oocyte,causing it to stop at metaphase II
Oogenesis After Puberty (S2-3)
•Each month after puberty, a few primary oocytes are activated •One from this group is "selected" each month to become dominant follicle that resumes meiosis I [see Q6 for details, but basically high estrogen inhibits FSH & LH, & ONLY the dominant follicle can withstand this drop in FSH & LH, all the rest deteriorate] •After division of meisosis I is completed, two haploid cells of different sizes are produced: - Secondary oocyte [haploid/23 chromosomes]: large cell with almost all of mother cell cytoplasm and organelles - First polar body: small cell almost devoid of cytoplasm [& organelles. pm just takes away the other chromosome]. •Secondary oocyte [ENTERS meiosis II but cannot finish it unless fertilized so#]arrests in metaphase II and becomes the ovulated ovum. •If not penetrated by sperm, it deteriorates. •If penetrated by sperm, second oocyte completes meiosis II, yielding: - Ovum (functional gamete) - Second polar body [all polar bodies degenerate]
Homeostatic Imbalance [of uterine cycle] (S31)
•Extremely strenuous physical activity can delay menarche in girls and disrupt normal menstrual cycle in adult women -Can cause amenorrhea, cessation of menstruation
21. Learn the human developmental stages after fertilization (S34)
•Fertilization: fusion of ovum [nrly 'ovum', but "secondary oocyte"] and sperm on day one, making a "zygote" {[& secondary oocyte continues meiosis II]} •Morula: solid ball of cells after three days •Blastocyst: hollow ball of cells after five days •Trophoblast: forms early embryo, fetal membranes and placenta after five to seven days •Embryo: EMBRYONIC PHASeE = 4th to 8th weeks1 'the developing human from fertilization to the eighth week of pregnancy' [see slide 40 cuz actually the 1st to 3rd week is still the pre-embryonic phase.] •Fetus: 9 weeks to birth at around 40 weeks •Neonate: newborn/ from birth to 28 days. •Infant: baby aged less than 1 year.
10. What will happen with the corpus luteum if fertilization does not occur? (S17)
•If no pregnancy occurs, corpus luteum degenerates as the progesterone goes down, into corpus albicans (scar) in 10 days [corpus luteum = a term meaning "yellowish body"] -Corpus luteum deteriorates as LH starts to go down. There is a decrease in estrogen and progesterone which ends blocking of FSH and LH secretion which causes cycle to begin again. -Luteolytic or ischemic phase: last 2-3 days of luteal phase, when endometrium begins to erode. Note: IF pregnancy occurs, corpus luteum produces hormones that sustain pregnancy until placenta takes over, at about 3 months.
22. What are the 3 phases of human development? (S35)
•Pre-embryonic phase (1-3rd wk) •Embryonic phase (4- 8th wk) •Fetal phase (9th to birth)
27. Presence of what hormone is used in pregnancy tests? (S43)
•The 3rd week of development •Development of the Neural tube (CNS) •Secretion of Chorionic Gonadotropin hormone (CGH) that stimulates mother ovaries to secrete Progesterone through the pregnancy. (CGH is used for test for pregnancy).
