Pregnancy recognition Flashcards
(25 cards)
define syngamy
fusion of the male and female pronuclei.
define embryo
Oamsim in the early stages of development, these all look very similar and are hard to distinguish between species.
define fetus
potential offspring that is still within the uterus that can be distinguished from other species,
define conceptus
The product of conception, it is an umbrella term which includes, embryo, fetus, extraembryonic membranes and placenta during the post-attachment phase.
define ootid
when the male and female pronuclei can be observed. This is the largest single cell and has a large cytoplasmic volume compared to the nucleic body. This allows the cytoplasm to split into many more cells.
whar are four major steps that must occur before the embryo can attach to the uterus.
development within the zona pellucida (division)
Blastocyst hatching from the zona pellucida
Maternal recognition of pregnancy
Extraembryonic membrane formation
describe the development within the zona pellucida that occurs
The cell undergoes many mitotic divisions (cleavage divisions), this is aided by the large volume of cytoplasm in the cell of the ootid.
The first division produces a two celled embryo which are called blastomeres, these produce many more daughter cells.
When cells have divided to the point of uncountable this structure is then called a morula
Once the inner and outer cells are more defined a sodium pump causes fluid to build in the center of the morula. This ionic change favors diffusion of water into the cell and the fluid formas a blastocoel which is a fluid filled cavity.
Blastomeres from the 2, 4 and 8 celled embryos are called ….
totipotent
within the morula there is inner and outer cells, what are they key diffrence between them
the outer become condensed forming tight junctions and the inner cells develop abundent gap junctions. Gap junctions allow for cellular communication.
what is there not cellular growth in the morula
the zona peelucida prevents and size change from the begining ootid size.
in the blastocyte, what are the two segment called?
inner cell mass (ICM) and trophoblast
during hatching what occurs
the blastocyte produces enzymes that degrade the zona pellucida
Once a small crack occurs on the zona pellucida, the cells escape and become a free floating embryo in the lumen of the uterus.
During the next 24 - 48 hours rapid mitosis occur
where are the enzymes produced from in the blastocyte to causes hatching
proteolytic enzymes by the trophoblastic cells.
During free floating of the embryo survival is reliant on:
Adequate luteal function
Adequate progesterone synthesis
Uterus responsiveness to progesterone.
what do the extraembyronic membrane form from
Each extraembryonic membrane steam from either the trophoblast, endoderm, mesoderm and the embryo
how to the dermal trilaminar disc form
This quickly developed to the beginnings of the embryo, the mesoderm and endoderm. The cells for the endoderm and migrating to the button and forming a sphere under the mesoderm.
what are the extraembryonic membranes and their function
yolk - temp placenta
amnion - protectice sac and waste storage
allantois - 2nd temp placenta
chorion - attachment site for the fetal and maternal placentas
how does the yolk sac form
The migrating endoderm forms the yolk sac and the mesoderm cells split and migrate around the yolk sac.
where does the allantois form
The allantois form beside the yolk sac and the mesoderm under the yolk sac fuses
as the amniotic fold elongate what does the yolk sac do?
yolk sac regresses and the allontosis grows larger
Finally the allantoic folds fuse, how does this effect the structure
This forms a double sac around the embryo. (first sac is the newly formed amniotic cavity and the second is the achorion). By this point the allantois is extremely large and in respect to the regressed yolk sac. The fusion of the allantois and the chorion forms the allantochorion
Key hormonal process in recognition of the embryo which can kill it if not stopped
Oxytocin produced from the corpus luteum is received by the endometrial cells via a threshold number of receptors. This causes the synthesis of PGF2a which is released in a pulsatile manner. Luteolysis occurs after this causing the death of the embryo.
Note that if there are not enough receptors in the endometrial cells (dependent on the period of the cycle) then PGF2a will not be released and luteolysis will nor occur.
This process must be stopped if we want a successful pregnancy
how does the cow and ewe prevent the luteolysis caused from the PGF2a
The trophoblast cells in the blastocyst produce a interferon protein called bovine interferon T / ovine interferon T (INF-T). These proteins bind to the oxytocin receptors on the endometrial cell, preventing the PGF2a synthesis and release.
INF-T also causes the production of protein in the uterine gland, these are secreted into the uterine lumen to nourish the embryo.
how does the sow prevent the luteolysis caused from the PGF2a
In the sow luteolysis is caused by the oxytocin from the posterior pituitary, endometrial cells and the corpus luteum which promote PGF2a in the endometrial cells. PGF2a then diffuses into the capillaries and travels through the uterine vein into the ovaries and induced luteolysis.
To prevent this the blastocyst releases estradiol which will reroute the PGF2a into the uterine lumen. There it will be destroyed and hence prevent luteolysis.
There must be at least two concepts in each uterine horn for pregnancy to be maintained in the sow. If not PGF2a will be secreted causing termination.
