22 - Early Embryogenesis & Endocrinology of Gestation Flashcards
Four steps in pre-attachment embryonic development
- Development within the zona pellucida
- Hatching from the zona pellucida
- Maternal recognition of pregnancy
- Extra-embryonic membranes
What is an ootid
Oocyte after the 1st meiotic division in which the 1st polar body is present
What is syngamy
Fusion of the male and female pronuclei within the cytoplasm of a newly fertilized oocyte, giving rise to a zygote
What is a zygote
Diploid cell resulting from fusion of the male and female pronuclei
What is an embryo
Animal in the early stages of development that has not taken on an anatomical form that is recognizable as a member of a species
What is a fetus
Unborn young that possesses identifiable features of a given species
What is conceptus
A product of conception including:
- embryo in early development (preimplantation)
- fetus and placenta (postimplantation)
During fertilization, syngamy…
occurs to produce a zygote that begins to go cleave (mitotic division) to give rise to blastomeres
Cleavage step in pre-attachment embryonic development
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
Two groups of cells that form the morula? Through the process of…
- outer cells (adhesions create tight junctions between cells)
- inner cells (connected by gap junctions between cells)
Through compaction
What happens during blastcoele development
- 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
What happens during blastocyst hatching in pre-attachment embryonic development
blastocyst eventually “hatches” from the zona pellucida
Three main factors causing hatching of blastocyst
- growth and accumulation of liquid within the blastocyst
- enzymes from the trophoblast that degrade the ZP
- contractions of the blastocysts
Slides 7-13
Pre-attachment embyronic development **
Successful pregnancy maintenance requires… Why?
High blood progesterone concentrations
Prostaglandin F2a induced luteolysis must be prevented
Maternal recognition of pregnancy in cow & ewe? Sow?
Cow & ewe: blastocyst(s) produce interferon to prevent luteolysis
sow: blastocysts produce estradiol to prevent lutoelysis. Number of conceptus is important
Maternal recognition of pregnancy in the mare? Bitch & queen?
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**
Luteolysis depends on… (3)
- presence of oxytocin receptors on uterine endometrium
- oxytocin production by the large luteal cells
- PGF2a synthesis by uterine endometrium
Role of interferon (IFN) in cow/ewe
Produced by blastocyst and inhibits the oxytocin-receptor development so that oxytocin cannot stimulate PGF2a production by the uterine endometrium
Role of estradiol in the sow
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
Maternal recognition of pregnancy in the mare more in depth
Migration of the conceptus over the uterine endometrium distributes factors that significantly reduce the production of PGF2a
Slide 21
Hormones of pregnancy/parturition
Pregnancy:
- early pregnancy factor (EPF)
- progesterone
- equine chorionic gonadotropin (eCG in mares only)
Parturition:
- adrenal corticotropin
- estrogens
- PGF2a
- relaxin
- oxytocin
What is early pregnancy factor (EPF)**
- 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
EPF found in what species? has been used to develop…
Human, cattle, sheep and pigs
Early pregnancy test based on EPF has been developed
Describe progesterone. Provides…
- 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
Describe progesterone production
- levels of P4 vary with species (up to 40ng in pigs)
- produced by CL in early pregnancy
- placenta eventually takes over production
How does the role of CL & placenta in P4 production vary among species
- 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)
Slide 27-29
Timing of placental takeover for P4 production
Progesterone profiles
Describe equine chorionic gonadotropin (what makes it, when)
- 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
What is the role of eCG
- 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
Effects of eCG injected into other species
Strong FSH-like effects and often used as part of superovulation protocoles
Slide 33
CL P4 output in the mare
Uterine endometrium produces various…
growth factors and cytokines that stimulate growth and development of the fetus in utero
