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AN SC 312 > 22 - Early Embryogenesis & Endocrinology of Gestation > Flashcards

22 - Early Embryogenesis & Endocrinology of Gestation Flashcards

1
Q

Four steps in pre-attachment embryonic development

A
  1. Development within the zona pellucida
  2. Hatching from the zona pellucida
  3. Maternal recognition of pregnancy
  4. Extra-embryonic membranes
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2
Q

What is an ootid

A

Oocyte after the 1st meiotic division in which the 1st polar body is present

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3
Q

What is syngamy

A

Fusion of the male and female pronuclei within the cytoplasm of a newly fertilized oocyte, giving rise to a zygote

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4
Q

What is a zygote

A

Diploid cell resulting from fusion of the male and female pronuclei

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5
Q

What is an embryo

A

Animal in the early stages of development that has not taken on an anatomical form that is recognizable as a member of a species

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6
Q

What is a fetus

A

Unborn young that possesses identifiable features of a given species

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7
Q

What is conceptus

A

A product of conception including:
- embryo in early development (preimplantation)
- fetus and placenta (postimplantation)

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8
Q

During fertilization, syngamy…

A

occurs to produce a zygote that begins to go cleave (mitotic division) to give rise to blastomeres

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9
Q

Cleavage step in pre-attachment embryonic development

A

Cleavage of the blastomeres continues (2-celled -> 4-celled -> 8-celled embryo) until a ball of cells within the zona pellucida is formed referred to as a morula

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10
Q

Two groups of cells that form the morula? Through the process of…

A
  1. outer cells (adhesions create tight junctions between cells)
  2. inner cells (connected by gap junctions between cells)

Through compaction

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11
Q

What happens during blastcoele development

A
  • Two groups of cells form in the morula
  • sodium pumped into the intracellular spaces and water follows osmotically (fluid accumulates in morula)
  • fluid accumulation causes outer cells to flatten & blastocoele forms
  • two separate cellular components (ICM and trophoblast) merge
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12
Q

What happens during blastocyst hatching in pre-attachment embryonic development

A

blastocyst eventually “hatches” from the zona pellucida

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13
Q

Three main factors causing hatching of blastocyst

A
  1. growth and accumulation of liquid within the blastocyst
  2. enzymes from the trophoblast that degrade the ZP
  3. contractions of the blastocysts
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14
Q

Slides 7-13

A

Pre-attachment embyronic development **

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15
Q

Successful pregnancy maintenance requires… Why?

A

High blood progesterone concentrations

Prostaglandin F2a induced luteolysis must be prevented

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16
Q

Maternal recognition of pregnancy in cow & ewe? Sow?

A

Cow & ewe: blastocyst(s) produce interferon to prevent luteolysis

sow: blastocysts produce estradiol to prevent lutoelysis. Number of conceptus is important

17
Q

Maternal recognition of pregnancy in the mare? Bitch & queen?

A

Mare: proteins/estradiol synthesis and contact of the conceptus with endometrium prevents luteolysis

Bitch & queen: does not require a signal from the conceptus (lifespan of the CL is longer than the gestation period)

Slide 17**

18
Q

Luteolysis depends on… (3)

A
  • presence of oxytocin receptors on uterine endometrium
  • oxytocin production by the large luteal cells
  • PGF2a synthesis by uterine endometrium
19
Q

Role of interferon (IFN) in cow/ewe

A

Produced by blastocyst and inhibits the oxytocin-receptor development so that oxytocin cannot stimulate PGF2a production by the uterine endometrium

20
Q

Role of estradiol in the sow

A

Produced by the blastocyst (trophoblast cells) and causes PGF2a production by the uterine endometrium to be rerouted into the uterine lumen where it is destroyed

21
Q

Maternal recognition of pregnancy in the mare more in depth

A

Migration of the conceptus over the uterine endometrium distributes factors that significantly reduce the production of PGF2a

Slide 21

22
Q

Hormones of pregnancy/parturition

A

Pregnancy:
- early pregnancy factor (EPF)
- progesterone
- equine chorionic gonadotropin (eCG in mares only)

Parturition:
- adrenal corticotropin
- estrogens
- PGF2a
- relaxin
- oxytocin

23
Q

What is early pregnancy factor (EPF)**

A
  • protein (chaperonin 10) expressed into the maternal circulation prior to embryonic attachment
  • shown to have immunosuppressive properties (inhibits female immune system during critical stage of embryonic dev)
  • produced in endometrial cups
24
Q

EPF found in what species? has been used to develop…

A

Human, cattle, sheep and pigs

Early pregnancy test based on EPF has been developed

25
Q

Describe progesterone. Provides…

A
  • dominant hormone of pregnancy
  • essential for embryonic/fetal dev to prevent return to estrus and produce uterine env appropriate for implantation

Provides “progesterone block” that inhibits myometrial contractions during pregnancy

26
Q

Describe progesterone production

A
  • levels of P4 vary with species (up to 40ng in pigs)
  • produced by CL in early pregnancy
  • placenta eventually takes over production
27
Q

How does the role of CL & placenta in P4 production vary among species

A
  • ewe & mare: placenta takes over in early gestation
  • cow: placenta takes over in late gestation
  • sow, bitch and queen: CL is source of P4 throughout gestation (NOT placenta)

CL continues to produce P4 throughout pregnancy in all these species (stops = abortion)

28
Q

Slide 27-29

A

Timing of placental takeover for P4 production
Progesterone profiles

29
Q

Describe equine chorionic gonadotropin (what makes it, when)

A
  • Gonadotropin produced by endometrial cups of the placenta
  • cups begin to form & express eCG at the time of attachment
  • cup dev & eCG secretion peaks midway through first trimester
  • cups regress & eCG secretion bottoms out by ~100 days of gestation (placenta takes over)

Slide 31

30
Q

What is the role of eCG

A
  • maintains CL production of P4 during the first trimester (maintains the primary CL and as eCG increases mare will ovulate (d40-70) to create an accessory CL which takes over P4 production)
  • placenta assumes major P4 producing role ~100d gestation
31
Q

Effects of eCG injected into other species

A

Strong FSH-like effects and often used as part of superovulation protocoles

32
Q

Slide 33

A

CL P4 output in the mare

33
Q

Uterine endometrium produces various…

A

growth factors and cytokines that stimulate growth and development of the fetus in utero

AN SC 312 (31 decks)

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