The Follicular Phase of the Estrous Cycle Flashcards
(92 cards)
1
Q
what are the 4 major events of the follicular phase?
A
- elevated gonadotropin secretion from anterior pituitary
- follicular growth and preparation for ovulation
- sexual receptivity
- ovulation
2
Q
what is the driving force for initation of the follicular phase?
A
luteolysis (of previous CL)
3
Q
list the cascade of events that occur in response to luteolysis
A
- decreased progesterone
- negative feedback removed
- increased amplitude (concentration) and frequency of GnRH
- initial increase of FSH and LH
- increased estradiol
4
Q
what triggers the LH surge in spontaneous ovulators?
A
high levels of E2
5
Q
what triggers the LH surge in induced ovulators?
A
high levels of E2 and neurological stimulation
6
Q
does a follicle have to be at a certain stage to undergo atresia?
A
no, any follcile at any stage can undergo atresia
7
Q
what percent of monovulatory follicles undergo atresia?
A
99%
8
Q
what is superovulation?
A
the process of rescuing follicles from undergoing atresia with FSH treatment
9
Q
about how many follicles is a cow born with?
A
100,000
10
Q
how many follicles does a cow have at 100 days of gestation (pre-birth)?
A
2.9 million
11
Q
how many follicles does a cow have at 12 months of age?
A
75,000
12
Q
how many follicles does a cow have between 4-6 years old, her peak breeding years?
A
21,000
13
Q
how many follicles does an aged cow have?
A
2,500
14
Q
what does a cow enter at 20-25 years of age?
A
reproductive scenesence, equivalent to menopause
15
Q
what is cyclic recruitment, or emergence?
A
phase when a group (cohort) of a small antral follicles begin to grow and secrete estradiol
16
Q
what is selection?
A
recruited follicles get selected to become dominant or undergo atresia
17
Q
what is dominance?
A
large antral follicle in final stage of maturation
18
Q
what happens to a dominant follicle in the presence of high LH?
A
ovulation
19
Q
what happens to a dominant follicle in the presence of low LH?
A
atresia
20
Q
describe the difference between atresia and necrosis?
A
atresia is the moderated, clean, organized, non-infectious process of destroying follicles through apoptosis; necrosis is never good!!
21
Q
what is atresia?
A
degeneration of follicle prior to ovulation
22
Q
what are the 2 stages of initial follicular growth?
A
- initial recruitment
2. cyclic recruitment
23
Q
which phase of follicular growth is gonadotropin independent?
A
initial recruitment
24
Q
how long does initial recruitment last?
A
50-60 days
25
how long does cyclic recruitment last?
only a few days
26
what does gonadotropin independent mean for follicular growth?
does not require LH or FSH
27
when does cyclic recruitment begin?
when small antral follciles get FSH receptors
28
what are follcilular waves in accordance with?
CL lifespan
29
what happens if the dominant follicle is ready when a CL is still present?
no signal to ovulate, leading to atresia and a new wave
30
what intiates recruitment?
high levels of FSH
31
describe FSH, E2, and inhibin levels during selection
FSH low from negative feedback, high E2 and inhibin furhter lower FSH
32
describe FSH, E2, and inhibin levels during dominance
FSH is VERY low, E2 and inhibin are VERY high
33
decribe FSH levels after atresia
FSH increasing again
34
what happens to the developing follicle during dominance?
follicle starts getting LH receptors in granulosa cells; follicle can now respond to LH for continued growth
35
will a 2-wave or a 3-wave cycle have longer follicular waves?
2- wave cycle
36
list the steps of LH producing E2 (3)
1. LH signals to theca cells to produce testosterone using cAMP pathway
2. testosterone diffuses into granulosa cell
3. FSH drives conversion of testosterone to E2 using the cAMP pathway
37
why will only a dominant follicle ovulate in response to LH?
only dominant follicles have receptors for LH
38
list the 8 effects of estradiol on the repro tract and brain
1. hypothalamus for GnRH surge
2. increased blood flow
3. genital swelling
4. change in tissue electrical conductivity
5. leukocytosis: removal of foreign cells from repro tract after mating, including sperm
6. increased mucosal secretion: physical protection during mating and sperm selection in ruminants
7. initiation of uterine gland growth: support embryo before attachment
8. elevated myometrial tone: contractions for sperm transport
39
list the 3 behavioral effects of estradiol
1. lordosis
2. phonation
3. physical activity: restless
40
define ovulation
the purposeful destruction of a follicle for ovum/oocyte release
41
list the 6 tissue layers that must break down in an ovarian follicle to release the ovum from innermost to outermost
1. granulosa
2. basement membrane
3. theca interna
4. theca externa
5. tunica albuginea
6. germinal epithelium
42
where does the break down of tissue layers to release the ovum occur?
on the opposite side of where the ovum is
43
what 4 events MUST happen in order for ovulation to occur?
1. protein synthesis
2. steroid synthesis: E2 to P4
3. prostaglandin synthesis
4. plasminogen activator synthesis
44
what is the result of cumulus expansion?
oocyte separates from follicular wall
45
what causes cumulus expansion?
hyaluronic acid and protein production
46
what is a stigma?
a weakened spot where ovulation or "pop" will occur
47
what 4 events does the preovulatory surge cause? (hint: it's the 4 things needed for ovulation)
1. cumulus expansion
2. shift from E2 to P4 by dominant follicle
3. increase in PGF2a
4. histamine reaction and increase in PGE2
48
what cascade of events is caused by the shift from E2 to P4 by dominant follicle?
increase in P4, causing increase in collagenase, which weakens the follicular wall for ovulation
49
what cascade of events is caused by the increase in PGF2a from the preovulatory LH surge?
release of lysozomal enzymes also weakens the follicular wall for ovulation, AND contractions of smoother muscle increase follicular pressure for ovulation
50
what cascade of events is caused by the histamine reaction and increased PGE2 from the preovulatory LH surge?
increased blood flow to ovary and follicle leads to edema (from fluid buildup), which increases follicular pressure for ovulation
51
what 3 factors cause ovulation as the result of the 4 main events that occur
1. oocyte separated from follcular wall
2. follicular wall weakens
3. follicular pressure increases
52
what does collagenase do?
breaks down collagen, which usually hold cells together
53
what are the 2 types of ovulators? describe them
1. spontaneous: ovulate in response to feedback loop
| 2. induced: ovulate in response to mating
54
what causes cats to ovulate?
physical stimulation of nerves in vagina and cervix
55
what causes camelid to ovulate?
a chemical in the seminal plasma
56
list the 6 steps of the cat ovulation pathway/feedback loop
1. copulation stimulates sensory nerves in the vagina and cervix
2. impulses sent to spinal cord
3. impulses relayed to surge center in hypothalamus
4. GnRH surge
5. LH surge
6. ovulation
57
what type of pathway is the ovulation of a cat
neuroendocrine
58
how successful is single copulation for cats?
works 50% of the time
59
what do multiple copulations lead to in a cat?
higher LH surge
60
what is oogenesis?
the creation of an ovum
61
what is an ovum?
female gamete
62
what is a primordial germ cell? (4)
a cell that gives rise to gametes, is not sex specific, is present during the prenatal period, and migrates to the genital ridge for later gamete production
63
what is an oogonia? (3)
an undifferentiated germ cell that will give rise to an oocyte, will undergo mitosis to increase numbers, and will get surrounded by follicle cells which initiates meiosis all during the prenatal period
64
what is a primary oocyte?
an oocyte during its growth phase and before it completes its first meiotic division
65
when does an oogonia become a primary oocyte?
prenatally
66
in what phase does an oocyte spend most of its lifespan?
as a primary oocyte
67
how long does an oocyte stay a primary oocyte?
until ovulation
68
what is dictyate?
arrest during prophase of Meiosis I
69
what 2 types of maturation must a primary oocyte undergo?
1. nuclear: ability of a cell to divide
| 2. cytoplasmic: ability to form an embryo when relevant
70
what initiates the change from primary to secondary oocyte in a dominant follicle?
LH surge
71
what is a secondary oocyte?
the resulting oocyte after meiosis I is complete
72
what does uneven cytokinesis in meiosis I result in?
a polar body that has minimal cytoplasm by 1/2 the female chormatids
73
can the polar body be fertilized? what happens to it?
generally not; wil degenerate
74
what happens to the remaining part of the oocyte after the polar body is kicked out?
will enter meiotic arrest again
75
what is the perivitelline space (PVS)?
space between zona pellucida and oocyte
76
what happens if an oocyte is not fertilized?
it will not resume meiosis, will just die off
77
what does meiosis II trigger?
1/2 the female chromosomes to be kicked out to make room for the male half
78
what is trisomy?
when one chromosome is not kicked out into the polar body, results in abnormalities
79
in what follicles are primary oocytes found?
primordial, primary, and growing follicles
80
why do oocytes have a limited lifespan?
because once activated, they must go in to meiosis II pretty quickly or die off
81
what is the prupose of tranzonal projections (TZP)?
keep open line of communication between corona radiata (cumulus cells) and follicle
82
what does TZPs contain that allow for communication?
gap junctions
83
describe the process of resumption of meiosis in oocyte before LH surge (3)
1. before the LH surge, cAMP in transported into oocyte through gap junctions in TZP
2. in meiotic (MI) arrest, high amount of cAMP in oocyte inhibits meiosis/maturation-promoting factor (MPF)
3. lack of MPF holds oocyte in meiotic arrest
84
describe the process of resumption of meiosis in oocyte in response to LH surge
1. gap junctions in TZP close
| 2. lower cAMP levels allows MPF activation
85
can ovulation occur if the gemete is ready, but the follcile isn't?
no, both cascades need to be timed perfectly so that BOTH are ready
86
what animals ovulate before resumption of meiosis after the LH surge?
dogs and foxes
87
when does sperm penetration occur for dogs and foxes?
when resumption of meiosis begins
88
when do most species ovulate?
after first polar body is emitted or arrest at meiosis II
89
when does sperm penetration occur for most species?
after ovulation
90
what is syngamy?
when male and female pronuclei fuse
91
what is a zygote? how long does it last?
from syngamy to first cell division, 18-24 hours
92
when is an embryo?
1st cell division and onward
