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Repro Bio 3 > Early pregnancy > Flashcards

Early pregnancy Flashcards

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1
Q

what is early transport of the zygote accomplished by (3)

A
  • muscular contractions of oviduct (a1 contraction, b2 relaxation adrenergic receptors)
  • ciliary beating on epithelial cells lining oviduct
  • oviductal fluid movements in response to these
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2
Q

how do embryos move within oviduct (esp ampulla)

A
  • to and fro rather than unidirectionally

- overall bias for movement toward uterus

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3
Q

what happens near the end of movement through oviduct

A

temporary arrest (days) at the ampullary-isthmic junction

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4
Q

what is purpose of arrest at ampullary-isthmic junction

A
  • initiated by embryonic signals to oviduct
  • ensures that it spends appropriate development time in the oviductal environment (vs being prematurely sent to the uterus where it would not survive)
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5
Q

what happens after arrest at ampullary-isthmic junction

A
  • rapid transport through isthmus
  • some species halt again at uterotubal junction prior to entry to uterus (tonic contraction of oviductal circular smooth muscle)
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6
Q

what is rate of transport under the influence of )3)

A
  • steroid hormones
  • paracrine factors
  • autonomic nervous system (b2 = relaxation, a1 = contraction) –> adrenergic stimulation of oviductal smooth muscle
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7
Q

what does estrogen usually do to transport and what is the exception

A
  • usually hastens transport

- slows it in the rabbit

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8
Q

how does embryo exert some control over oviductal transport

A

by secreting paracrine factors –> presence of embryo can either slow or hasten transport depending on the region

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9
Q

are embryos or unfertilized oocytes transported into uterus?

A
  • most species: both embryos and unfertilized oocytes transported into uterus
  • horse, donkeys, bats: only fertilized eggs (embryos) transported
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10
Q

what do equine embryos secrete from compact morula stage and why

A
  • secrete PGE2

- acts locally to relax circular smooth muscle layer of oviduct to embryo can progress

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11
Q

does embryo of unfertilized oocyte enter uterus first

A

embryo

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12
Q

where do most embryos develop in cows and sheep

A

uterine horn on the same side as the CL (ipsilateral aide) –> little tendency to migrate to achieve maternal recognition of pregnancy

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13
Q

where do most embryos develop in horses

A
  • single embryo migrates freely throughout uterus before it lodges at the base of one of the uterine horns
  • must contact entire endometrium in order to survive
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14
Q

embryo migration in camelids

A
  • equal distribution of ovulations from L and R ovaries

- 95% of pregnancies in L uterine horn

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15
Q

embryo migration in dog/cat/pig

A
  • migrate freely through both uterine horns to achieve even spacing prior to implantation
  • ensures adequate placenta available
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16
Q

what signals even spacing of embryos in dogs/cats/pigs

A
  • chemical signals from embryo (histamine, estrogens, prostaglandin)
  • stretching of uterine wall
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17
Q

one function of zona pellucida in embryo migration

A

prevention of premature embryo attachment during transport through oviduct (tubal pregnancy)

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18
Q

what must embryo do with zona following transport into uterus

A

escape zona pellucida to form a placenta and benefit from supportive uterine secretions prior to implantation (blastocyst stage –> blastocyst/zona hatching)

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19
Q

what has to occur for blastocyst/zona hatching to happen

A
  • blastocyst or uterine endometrium secretes enzymes (plasma, trypsin) that weaken the zona
  • blastocyst expands and contracts under influence of PGE
  • results in splitting of zona –> blastocyst deforms and squeezes through gap
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20
Q

what can happen after blastocyst/zona hatching

A

cells of trophoblast can now interact directly with those of uterine epithelium (endometrium)

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21
Q

what happens to embryos following hatching

A
  • exponential growth phase of elongation involving extraembryonic membranes
  • elongation commences on day 11 (ewe/sow), 14-15 (cow)
  • directed by products of endometrium secreted into hisotroph
22
Q

bovine embryo elongation

A
  • day 13: spherical, 3mm diameter
  • day 17: 25cm filamentous structure
  • day 18: extended into opposite uterine horn
  • due to hyperplasia of cells in trophoblast
  • embryo remains in horn ipsilateral to CL
23
Q

pig embryo elongation

A
  • rapid
  • day 10: 2mm spheres
  • day 11-12: 10mm cylinders
  • start elongating 30-40mm/hr
  • day 16: 100cm
  • early lengthening through cellular remodeling and reorganization, not hyperplasia (then hyperplasia takes over)
24
Q

purpose of embryonic elongation

A

having trophoblast contact all or close to as much of the uterine endometrium as possible to ensure maternal recognition of pregnancy

25
Q

equine embryo elongation

A
  • conceptus enclosed in a capsule
  • does not elongate in early pregnancy like in other species
  • ensures contact with large part of endometrium by moving around
26
Q

what hormone is required for establishment of pregnancy and why

A
  • progesterone from CL
  • creates uterine environment in which early embryo can survive and establish itself for implantation and development of placenta, fetal development, birth
27
Q

since most species have short cycles, what must happen to establish and maintain a pregnancy

A

way to subvert or prevent the process of luteolysis that causes the cyclic demise of the CL

28
Q

what is maternal recognition of pregnancy

A

process whereby the embryo signals its presence to the maternal system and prolongs the life of the CL to preserve its own existence

29
Q

2 ways embryo prolongs life of CL

A
  • supporting it with luteotropic signal

- producing antiluteolytic signal that prevents CL’s premature demise

30
Q

ruminant maternal recognition

A
  • luteolysis due to prostaglandin release from uterine endometrium in response to changing the effective estradiol/progesterone ratios toward end of luteal phase
  • ratio change induces increased endometrial oxytocin receptors, increased central oxytocin release –> prostaglandin secretion
  • back up system of luteal oxytocin release, counter-current exchange system
31
Q

luteolysis in ruminants and how it relates to migration

A
  • fairly unilateral phenomenon (prostaglandin from L uterine horn lyses CL on left ovary)
  • single pregnancy (embryo) has to exert influence in the horn on the side of the CL –> don’t migrate to opposite horn
32
Q

what does ruminant embryonic trophoblast secrete

A

interferon-tau (IFN-tau)

33
Q

prevention of luteolysis in ewes

A
  • trophoblast elongates rapidly from day 11, secretes IFN-tau from days 10-21 of pregnancy
  • IFN-tau acts on endometrium to block transcription of estrogen receptors
  • no increase in estrogen receptors –> no estrogen up-regulation of oxytocin receptor gene –> no release of PGF2a from endometrium –> CL continues to function
34
Q

prevention of luteolysis in cow

A
  • IFN-tau prevents up-regulation of endometrial oxytocin receptors
  • unclear if this in indirect (via action on estrogen receptor like in sheep) or direct action on oxytocin receptor gene
35
Q

what would you call system of maternal recognition in ruminants

A

antiluteolytic (protects CL by preventing release of prostaglandin)

36
Q

prevention of luteolysis in pigs

A
  • endocrine-exocrine theory of maternal recognition
  • PGF2a secretion is usually endocrine, goes to uterine vasculature and then CL
  • pregnant sow: direction changes –> discharged in exocrine manner into uterine lumen (sequestered)
  • need at least 2 embryos in each horn
37
Q

what would you call system of maternal recognition in pigs

A

antiluteolytic (prevents prostaglandin accessing the CL)

38
Q

prevention of luteolysis in mare

A
  • early pregnancy: conceptus produces small amounts of PGF2a and PGE –> uterine smooth muscle peristalsis
  • embryo moves throughout uterus
  • conceptus products act on endometrium to prevent PGF2a release
39
Q

what would you call system of maternal recognition in mare

A

antiluteolytic

40
Q

prevention of luteolysis in primates

A
  • luteolysis mediated at level of ovary
  • hCG produced by trophoblast is luteotropic signal
  • acts directly on CL to support it by maintaining an “LH” signal (hCG has LH-like activity)
  • induces neovascularization
41
Q

what would you call the system of maternal recognition in primates

A

luteotropic

42
Q

prevention of luteolysis in dogs and cats

A
  • long luteal phase
  • no current evidence for maternal recognition as described in other domestic species
  • pseudopregnant cat: CL has natural lifespan while gestation is longer (prolactin is luteotropic)
  • dogs: progesterone levels increased –> increased prolactin
43
Q

prevention of luteolysis in lab rodents

A
  • ultrashort cycle
  • sterile mating gives pseudopregnancy
  • function of CL needed for most but not all of gestation, need viable embryos for CL function
  • initial rescue of non-functional CL due to mating induced prolactin secretion
  • second rescue of CL in pregnant animals turns 12 day CL of pseudopregnancy into 17+ day CL of pregnancy –> prolactin, placental lactogens (luteotropic)
44
Q

cow and maintenance of pregnancy beyond maternal recognition

A
  • up to 150d: CL only
  • 150-250d: CL and placenta
  • 250-term: CL
45
Q

bitch and maintenance of pregnancy beyond maternal recognition

A

CL throughout

46
Q

queen and maintenance of pregnancy beyond maternal recognition

A

CL throughout

47
Q

sow and maintenance of pregnancy beyond maternal recognition

A

CL throughout

48
Q

goat doe and maintenance of pregnancy beyond maternal recognition

A

CL throughout

49
Q

ewe and maintenance of pregnancy beyond maternal recognition

A
  • first 55-60d: CL

- 60d-term: placenta

50
Q

llama/alpaca and maintenance of pregnancy beyond maternal recognition

A

CL throughout

51
Q

mare and maintenance of pregnancy beyond maternal recognition

A
  • first 90-100d: CL

- 100d-term: placenta

52
Q

what do placentas of some species produce instead of progesterone and why important

A
  • some produce proogestens
  • may not cross-react on assay (when placenta takes over, progesterone production levels within placenta may be far higher than those in systemic circulation)

Repro Bio 3 (6 decks)

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