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ip 11 theriogenology > 8,9: Physiology of the Estrous Cycle - Volkmann > Flashcards

8,9: Physiology of the Estrous Cycle - Volkmann Flashcards

1
Q

basis of FM repro system / cycles is?

A

follicular waves

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2
Q

goal of FM repro sys?

A

to produce an oocyte that can be fertilized at predictable time (or multiple in litter bearing species)

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3
Q

what happens to majority of follicles that the ovary produces?

A

they become atretic

few will ovulate

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4
Q

at what stage are oocytes arrested in ovary?

A

diplotene stage of meiosis 1

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5
Q

what holds the oocytes in arrest?

A

meiosis inhibiting factor/AMH

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6
Q

what produces meiosis inhibiting factor/AMH?

A

granulosa cells

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7
Q

describe primordial follicles?

A

resting oocyte that contains oocyte surrounded by a layer of granulosa cells

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8
Q

T/F - the source of follicles throughout the life of a FM is infinite

A

FALSE - finite

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9
Q

why does only 1 follicle develop at 1 time?

A

b/c the follicle past primordial stage has layer of granulosa cells that sec AMH, suppressing the development of others

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10
Q

diff btwn structure of primordial and primary follicles

A

primary have 2 layers of granulosa cells

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11
Q

secondary follicle?

A

several layers of granulosa cells and zona pellucida around oocyte

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12
Q

what distinguishes tertiary follicle from secondary?

A

has antrum

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13
Q

structure of tertiary follicle?

A

lined inside by granulosa cells anchored to basement membrane

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14
Q

what 2 layers of cells are loc either side of the basement membrane of tertiary follicle?

A

granulosa cells anchored to BM in follicle

theca cell populations loc on other side of BM

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15
Q

what are the 2 populations of theca cells? fxns?

A

theca interna cells - endocrine organs

theca externa cells - skeleton that surrounds follicle => fibrous tissue

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16
Q

what triggers initial development of follicular waves?

A

gonadatropins

FSH - basal levels

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17
Q

what triggers antral formation?

conversion from secondary to tertiary follicles

A

higher FSH levels

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18
Q

what triggers the rise in FSH levels that triggers antral formation?

A

GnRH dependent from hypo

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19
Q

what receptors are on granulosa cells?

A

FSH

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20
Q

what receptors are on thecal cells?

A

LH

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21
Q

as granulosa cells dev, what hormone do they produce?

A

e2

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22
Q

what changes does e2 cause on receptors of granulosa cells?

A

induces formation of more FSH receptors

cycle continues - b/c follicles are stimulated to make more e2, which makes more FSH receptors on granulosa cells so follicles can develop and make more e2…

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23
Q

where does antral fluid come from?

A

fluid is secreted by granulosa cells

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24
Q

T/F - once a follicle develops, it can arrest again later

A

FALSE - once it begins, it cannot stop

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25
Q

in species except for the dog, what stage oocyte is ovulated?

A

secondary oocyte

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26
Q

what stage oocyte is released in the dog?

A

primary oocyte - meiosis must finish before fertilization can occur

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27
Q

fxn of LH?

A

to promote the follicle to mature and drive rupture of follicle at ovulation

matures graffian follicle to ovulatory follicle - causes ovulation

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28
Q

after ovulation, what role does LH have?

A

governs conversion of e2 producing follicle to a p4 producing CL

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29
Q

besides e2, what hormone do granulosa cells produce?

A

inhibin

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30
Q

what does inhibin inhibit?

A

suppresses FSH release

w/o FSH, no follicle or gonadal fxn can occur

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31
Q

when inhibin levels are high and FSH levels are low, where do granulosa cells get support from?

A

LH -> which drives follicle to next stage of a CL

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32
Q

what do theca cells take in and what do they use it to produce?

A

take cholesterol from circulation and convert it to progestogen -> utilize LH to convert it to testosterone

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33
Q

after theca cells make testosterone, where does it go and what happens there?

A

testosterone goes from theca cells, across BM, into granulosa cells, where it is converted to estrogen

via aromatase enzyme

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34
Q

what happens to granulosa cells after ovulation and why can it happen so quickly?

A

converted to CL b/c they are poorly vascularized and are loosely attached

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35
Q

what is level and fxn of FSH after ovulation?

A

high b/c inhibin is gone

it promotes the follicular wave to develop

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36
Q

what is considered day 0 of cycle?

A

when FM ovulates and a new follicular wave starts

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37
Q

why does a new follicular wave start when the FM ovulates?

A

b/c the dominant follicle produced inhibin - it is gone now so no inhibin and other follicles can develop in new wave

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38
Q

what hormone spikes after ovulation and drives development of new folliclular wave?

A

FSH

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39
Q

what changes does LH surge cause at ovulation and what hormone is secreted as a result?

A

follicle becomes CL

CL produces p4

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40
Q

what are e2 levels just after ovulation?

A

low [b/c now a CL, no longer a graffian follicle]

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41
Q

as one dominant follicle emerges during the follicular wave, what hormonal changes does this trigger?

A

dom follicle produces inhibin
FSH sec decrease as result

also e2 being produced, positive feedback to surge center

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42
Q

with dec FSH levels, how does dom follicle survive?

A

granulosa cells of follicle now rely on LH - look for ovulatory surge of LH to ovulate

if LH is not there [due to high p4] then the follicle does not survive and become atretic

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43
Q

what hormone suppresses the ovulatory surge of GnRH and subsequent LH?

A

p4 - works at level of hypo

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44
Q

T/F - p4 suppresses release of LH at level of pit?

A

FALSE
it suppresses GnRH surge at level of hypo - NOT LH surge from pit

so: you can give a FM a dose of LH and she will ovulate, despite high p4 levels - b/c LH is not inhibited - GnRH is inhibited at hypo

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45
Q

as a follicle becomes atretic, what happens to the hormone profile it produces?

A

e2 and inhibin levels fall

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46
Q

as inhibin levels fall, what hormone is allowed to inc?

A

FSH

which stimulates another follicular wave to occur

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47
Q

what does p4 do to the surge center?

A

it primes it - it inhibits the release of GnRH but induces expression of e2 receptors - so when there are enough e2 receptors present, the GnRH surge can occur -> ovulation will result

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48
Q

how does e2 promote ovulation indirectly?

A

sec from dom follicle

positive feedback to GnRH surge center -> eventually causes GnRH surge -> LH surge follows -> ovulation success

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49
Q

at what stages of FM life is it hard to produce GnRH surge to initiate cycling?

A
  • pre puberty
  • post partum [every time]
  • post anovulatroy season [if seasonal animal]
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50
Q

clinically Tx FM to prime surge center by giving exogenous p4 using what products in what species?

A

regumate in mare
CIDR in cow
matrix in sow

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51
Q

T/F - e2, produced by large dom follicle, suppresses FSH secretion from pit gland.

A

False -> e2 does NOT suppress FSH sec

this was prior beliefs
now known: INHIBIN talks to ant pit to suppress FSH sec

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52
Q

t/f: in order to survive, all antral follicles require either FSH or LH or both

A

true

all viable follicles require gonadotropin support via FSH and /or LH

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53
Q

in spontaneously cycling animals, how can you start a new follicular wave?

A

by ending another one / the current one

make her ovulate the current follicle

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54
Q

why does ending one wave allow a new one to start?

A

b/c it gets rid of inhibin -> thus releasing suppression of FSH and allowing next wave to emerge in ovary

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55
Q

it is not uncommon for cows to have 2 or 3 follicular waves in one cycle. why is this NOT common in horses? horses tend to have only 1 follicular wave per cycle - why?

A

b/c mare has a drawn out LH surge (vs sharp LH surge of cow)

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56
Q

why is the prolonged LH surge of mare necessary?

A

b/c she ovulates 6-7 days after - so she is dependent on LH for follicle to survive

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57
Q

how do you shut off follicular development in mare?

A

e2 - shuts down ovaries - switch off follicular development

NOT inhibin - e2!

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58
Q

why does e2 shut down mare follicular development?

A

b/c e2 inhibits FSH secretion

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59
Q

immediately after ovulation, what structure is on the ovary?

A

corpus hemorrhagicum

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60
Q

why does corpus hemorrhagicum structure form?

A

collapse of follicle wall
disruption of BM (basement mem)
ingrowth of blood vessels
hemorrhage

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61
Q

after corpus hemorrhagicum develops, what cellular transformation occurs and what hormone does it secrete?

A

thecal cells [and maybe granulosa cells become luteal cells

luteal cells secrete p4

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62
Q

purpose of p4?

A

maintain pregnancy

therefore if not preg - get rid of p4 [source = CL]

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63
Q

what compound is converted into p4 by luteal cells?

A

cholesterol

64
Q

what is present in antral fluid that helps with appropriate clotting?

A

anti coagulant

so: if hemorrhage occurs before ovulation, blood will not clot
and if she ovulates and releases follicular fluid, hemorrhage is followed by clotting -> corpus hemorrhagicum

65
Q

developing CL occurs in what stages of estrous?

A

met estrus [occurring after estrus]

time btwn ovulation and mature CL

66
Q

what process yields solidification of CL?

A

hyperplasia of thecal cells and stromal tissue

67
Q

what is significant about met estrus stage CL?

A

insensitive to effects of PG

considered autonomous organ that cannot be destroyed

68
Q

what is significance / importance of having CL refractory to PG?

A

if pregnancy is established, CL must be refractory, to ensure pregnancy is maintained

69
Q

during met estrus, where is an embryo located?

A

in uterine tubes

in uterus by the time CL gains sensitivity to PGs [diestrus/anestrus]

70
Q

mature CL is what stage of estrous?

A

diestrus

71
Q

di estrus is what period of estrous cycle?

A

end of one heat to beginning of next heat [receptive
period]

so technicallly, met estrus and pro estrus are all a part of di estrus, b/c she is not receptive during these times

72
Q

if not preg, what happens to CL?

A

lysed

73
Q

what hormone lyses CL?

A

PgF2a (PG for short)

74
Q

what domestic species does not have luteolytic mechanism

A

dog

75
Q

where is PG F2a usually released from?

A

endometrium

76
Q

what is general function of prostoglandin molecules?

A

inflammatory mediators

77
Q

how does PG reach ovary from uterus in ruminants? in swine?

A

direct transfer of PG from uterine V into ovarian A - counter current exchange system for both

Ru: unilateral arrangement: PG from left uterine horn to left ovary and PG from R uterine horn to R ovary
swine: 2 uterine Vv are connected / anastomose so PG from either side can reach either ovary

78
Q

how does PG reach ovary in horses?

A

no counter current exchange mech - therefore PG must go through systemic circulation and metabolism in lungs

therefore horse is exceptionally sensitive to PG - a small amt reaches ovary and is required to lyse CL

79
Q

how does dog sensitivity to PG compare to horse and cow sensitivity?

A

dog extremely refractory CL so high dose needed to lyse CL - so high that side effects / systemic effects are too negative to dog

AND a dog dose would KILL a horse and cow

80
Q

length of cow estrous cycle

A

21 d

81
Q

what kind of cycle in cow?

A

non seasonal

poly estrous [one cycle leads to next]

82
Q

how long is estrus of cow?

A

12-18 hours

83
Q

when does cow ovulate relative to estrus?

A

12 hr after end of estrus

84
Q

on hormone profile, how can you find PG?

cow cycle

A

precedes fall in p4

b/c cause effect relationship

85
Q

how to find inhibin on cow cycle hormone profile?

A

opposite FSH

86
Q

describe mare estrous cycle?
estrus length?
ovulation timing?

A

seasonal (long day breeder)
polyestrous

estrus 3-8 days [long sexual receptivity]

ovulation on last or 2nd to last day of estrus

87
Q

MC day of standing estrus in mare?

A

last 2 days of estrus

88
Q

how long is LH surge in mare?

A

2-3 days

89
Q

how long is LH surge in cow?

A

short

90
Q

what action does hCG have?

A

LH like

91
Q

what % of large breed horses have tendency to double ovulate?

A

25%

twins are bad in horses

92
Q

what is and what is important about transitional estrus or spring heat in mare?

A
  • intermittent estrus, irregular or continuous heat
  • lasts 3 weeks (about 3 follicular waves)
  • first few waves secrete too little e2 to trigger ovulatory surge of GnRH
  • fxn is like ‘puberty’ - to prime surge center
93
Q

how does surge center get ‘primed’?

A

p4 primes it by inc e2 receptors on surge center -> allows positive feedback of e2 on surge center to trigger GnRH surge and LH surge and ovulation

94
Q

drug to manage transitional estrus in mare?

A

regumate

progestegin (p4 like compound)

95
Q

what is foal heat?

A

onset 5-10 days post foaling in mare

ovulation by day 18 post partum

highly fertile estrus

96
Q

what is typical timing of foal heat?

A

10 days post partum

97
Q

why might we skip the foal heat and not breed a mare at this time?

A

b/c it is highly fertile - but the subsequent estrus is even more fertile

greater chance of getting pregnant at estrus after foal heat

better to do this if she foaled early in season (consider 11 month pregnancy)

98
Q

when/why might it be important to breed FM in foal heat?

A

if she foals late in the season, shoot for foal heat breeding so next year, she will give birth earlier (consider 11 month pregnancy)

99
Q

what kind of cycle does ewe have?

length? ovulation timing?

A

seasonal [fall]
polyestrous

17 days

ovulation at end of estrus

100
Q

ewe gestation length

A

5 months

101
Q

for ewe, first ovulation after puberty and first ovulation of the season is more or less fertile?

does are the same

A

LESS

first diestrus is usually shorter than it should be
- if bred during first estrus of season, the short luteal period may be so short that she comes back into heat before her pregnancy is recognized so she will lose the first pregnancy

102
Q

doe estrous cycle?
length?
estrus?
ovulation timing?

A

seasonal [fall]
poly estrous

21 d cycle
estrus: 1 day

ovulation at end of estrus

103
Q

sow estrous cycle?
length?
estrus?
ovulation timing?

A 
non seasonal
poly estrous
cycle 21 d
estrus 1-4 d (MC 2 d)
ovulate 3/4 way through estrus (MC 36-44 hr after onset of estrus)
104
Q

sow has lactational anestrus. when she cycle post partum?

A

3-7 days after weaning

105
Q

estrous cycle of bitch?

A

monestrous
every 5-12 months
MC 6-7 mos

less than 5 mos and more than 1 year btwn cycles is abnormal

106
Q

what does monestrus mean?

A

one cycle does NOT lead to the next

no KNOWN physiologic connection btwn end of 1 and beginning of another cycle

107
Q

describe diestrus in most species and what about bitch diestrus is different:

A

other species: dominated by CL (luteal period) followed by anestrus; is the period btwn 2 estrus receptivities

bitch: inherently 2 diff phases
- luteal period dominated by p4 then p4 levels become basal and nothing happens

108
Q

unique about bitch endocrine estrous profile?

A

NO abrupt decline of p4 at end of luteal period

NO luteolytic mechanism
NO significant role of PGF2a, as in other species

109
Q

what is different in bitch CLs than in other species CLs?

A
  • CL of bitch has poor developed PG receptors

- to destory CL in bitch, b/c inherently refractory to PG, need BIG GUNS to destroy them - very high doses

110
Q

how long are bitch CLs considered autoonomous?

how does this compare with other species?

A
  • bitch: 25-30 days

- other species: 5 days

111
Q

what hormones does CL depend on in bitch after day 30?

A

prolactin and LH

112
Q

due to refractory CL, how to manage bitch cycle?

A
  • lots of PG -> but too many side effects

- wait a month after ovulation and do something to suppress prolactin or LH sec -> CL will wither away and cease to fxn

113
Q

when is the end of the luteal period in bitch? [met estrus]

A

there is not clear end

b/c no luteolytic mechanism that is known

114
Q

what / when trigger for onset of pro estrus in bitch?

A

not clear

115
Q

when does the luteolytic event occur in bitch? what is the purpose?

A

65 days post estrus - small luteolytic event - small PG surge

to destroy CLs - which are more receptive to PG effects

lysis is important to allow bitch to whelp

116
Q

when do you see inc in e2 levels in bitch? what is causing the inc?

A
  • massive inc in e2 levels before estrus

- prod by growing follicles

117
Q

duration of heat [estrus and pro estrus] in bitch?

A

16 days average

half pro estrus and half estrus

118
Q

hormone profile of bitch during pro estrus and estrus?

A

pro estrus: e2 and ends in LH surge

estrus: rising p4 levels [before ovulation]

119
Q

what hormone changes occur before, during and after estrus in bitch?

A

rising p4 before
LH surge
2 days later - ovulation

120
Q

how long is LH surge in bitch?

A

12 hrs

121
Q

on what day of the cycle does counting begin in bitch? and other species?

A

others: at ovulation
bitch: LH surge - b/c it is measurable and ovulation is not directly easily measurable

122
Q

in bitch, what hormone is used to indicate LH surge is near?

A

p4

123
Q

what hormone is most measurable in bitch to detect when ovulation will occur?

why?

A

p4 b/c it is harder to catch the LH surge b/c it is short lived

p4 inc 2 days before ovulation

124
Q

when it bitch most fertile?

why?

A

2 days after ovulation
4 days after p4 inc

b/c ovulatory oocyte needs to complete meiosis 2 before being fertilizable - bitch ovulates 1* oocytes and they must become 2* oocytes

125
Q

what is 2-2-2 rule? for what species does it apply?

A

p4 levels reach 2
ovulate 2 days later
fertile 2 days later

126
Q

how long are 2* oocytes fertilizable in bitch?

A

4 days

127
Q

T/F - the mathematical opportunity for cow is less than a bitch b/c she is in standing estrus for a longer duration for each cycle

A

false - mathematics works out so that amount of time in estrus is same annually across species - duration of estrus and frequency of estrus works out so fertile time is approximately equal over annual basis

128
Q

queen type of cycle?

A

induced ovulator w 3 or more matings

seasonal polyestrous

129
Q

what is duration of non pregnant luteal period in queen?

A

30-35 days

130
Q

what stimulates queen to ovulate?

A

coitus stim GnRH surge - vaginal stimulation by spines on Tom penis
more stimulation means more GnRH and higher likelihood of ovulation

131
Q

t/f: non preg queen has a luteolytic mechanism

A

false - no luteolytic mechanism known in queen

132
Q

t/f: preg queen has non luteolytic mech?

A

false - preg queen has luteotrophic mech to extend life of CLs

133
Q

how long do CLs live in not preg queen?

in preg queen?

A

30 days if not preg

duration of pregnancy if preg

134
Q

why don’t queen or bitch need / have maternal recognition of pregnancy mechanism?

A

b/c one cycle is not immediately followed by another cycle

they are NOT programmed to start a new cycle by default

135
Q

camelid estrous cycle?
ovulation timing?
luteal period if not preg?

A

seasonally poly estrous
non seasona lin USA

ovulate 24 h post breeding - induced ovulators

non preg luteal period is 11-12 days

136
Q

what stimulates camelid ovulation?

A

compound of seminal plasma of M induces GnRH surge

can be injected sub q and also work

137
Q

if hembra mates but is not preg, how long before she cycles again?

A

14 days

138
Q

how long post mating before you can measure inc p4 levels in preg hembra?

A

14 days

139
Q

what hormone is measured in hembra blood to confirm preg?

what does this hormone indicate?

A

p4

indicates that she is maintaining her CL - suggestive of pregnancy

140
Q

puberty 1* determined by what?

A

body weight relative to adult body mass

2/3

141
Q

what variables affect puberty onset?

A
  • body weight relative to adult body mass
  • 2* photoperiod
  • reversal of e2 inhibition on pituitary LH sec
142
Q

t/f: first estrus typically fertile and luteal phase long

exception to the rule?

A

false - first estrus usually silent (no ovulation)
AND luteal phase often short

exception? bitch

143
Q

pre pubertal - e2 inhibitory or stimulatory to LH surge?

A

inhibitory

144
Q

what is required to lift reverse inhibitory effects of e2 before puberty on GnRH surge center?

A

p4 priming

145
Q

t/f - domestic animals often experience reproductive senescence later in life

A

false - mare might

humans and primates do

146
Q

what species is seasonality most outspoken in?

A

mare
sheep
queen

147
Q

what hormone regulates seasonality?

A

melatonin

148
Q

what secretes melatonin?

A

pineal gland

149
Q

melatonin is secreted in response to what stimulus?

A

darkness

150
Q

how does melatonin regulate cyclicity?

A
  • darkness stim sec
  • inhibits GnRH pulse generator in mares
  • stimulates GnRH pulse generator in ewes
151
Q

t/f: manipulating daylight exposure can completely control estrous cyclicity in seasonal animals

A

false - photoperiod fine tunes cyclicity
even with day lenght appropriate to favor cyclicity in animals, she will still enter a period of anestrus at some point in the year - her body will randomly decide when

152
Q

what species is lactational anestrus?

A

sows

a little bit in beef cows

153
Q

how to get post partum sows to cycle?

A

wean them

154
Q

effects of M pheromones on FM reproduction?

and FM hormones on M?

A

M pheromoneinduces estrus beh in sows
FM pheromones provoke sexual interest in M dog
“ram effect” - ram induces cyclicity in ewes and also seen with pre pubertal gilt exposure to boar
bruce effect of rats - M causes abortion in pregnant rats

155
Q

effects of nutrition on cyclicity?

A

age and BCS at puberty
nutrition plane to begin cycling after birth again

flush feed ewes to gain seasonal advances on cycles

spring grazing lush pastures advances 1st ovulation in transition mare

ip 11 theriogenology (15 decks)

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