Post implantation and placenta development Flashcards
What does the zona pellucida do?
Prevent the early embryo from adhering to anything along its path to the uterus
What does the embryo need to do when it reaches the uterus?
It needs to hatch from the zona pellucida and implant itself on the uterine wall
At what day in the development does the embryo adhere itself onto the uterus wall? What is the epithelium lining of the uterine wall? What is the embryo called at this stage?
Day 7 Endometrium A blastocyst
Does the implantation process have a high success rate? Why?
No as at least half of embryos are lost prior or during implantation It may be a mechanism that prevents the development of embryos with genetic abnormalities
What part of the uterus is the embryo supposed to hatch onto? What is it called when it does not hatch onto the right part of the embryo?
The posterior wall If not here then it is called a ectopic pregnancy
What are the types of ectopic pregnancies? Which is the most common
Tubal pregnancy, ovarian pregnancy and abdominal pregnancy
What is the condition called when a blastocyst specifically hatches from the zona pellucida in the uterine tube? What can be the result of this?
Tubal pregnancies Can cause death to the mother as the uterus grows and cause the uterine tube to rupture
Where do ovarian and abdominal pregnancy occur?
Ovarian = ovary (where the eggs are stored FYI) Abdominal = abdomen
What happens during development and to the foetus if the embryo implants near the cervix of the uterus?
The placenta will form across the out of the cervical canal and possible lead to premature separation of the placenta late in pregnancy, can cause death of foetus
Label the diagram
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How does syncytial trophoblasts differ from cellular trophoblasts?
Syncytial are a large multinucleate cell with a large shared cytoplasm, cellular are individual cells
What happens to the syncytial trophoblasts and what does it do to the mothers tissue?
It grows larger and dissolves the mothers uterine tissue and endothelium tissue of the blood vessels within the uterus
By dissolving the endothelium tissue of the mothers blood vessels, what does this create and where is it made?
Creates lacunae (lacuna for individual one FYI) in the syncytial tissue
What are lacunae?
Pools of the mothers blood that accumulate in the syncytial tissue
What is done with the blood in the lacunae? What does this allow?
The syncytial tissue sends projections into the lacunae This allows the nutrients from the mothers blood to be diffused into the embryo from a young age
As an embryo develops are the lacunae still used for nutrient and waste transport? Why?
No because as the embryo gets bigger diffusion is no longer sufficient to transport the necessary material
What is extra-exmbyonic mesoderm? Where does it come from?
It is any mesoderm tissue that is not inside the embryo itself Comes from the junction between epiblast and hypoblast
What does extra-embryonic mesoderm do in early embryonic development?
It surrounds the entire embryo by forming extra-embryonic coelom
Explain the layers of the embryo
-The outside layer/shell are the syncytial trophoblasts, cellular trophoblasts and extra-embryonic coelom -The inside is the embryo (made of the three germ layers) -Connection to the outside from the embryo by the extra-embryonic stalk
Explain how the extra-embryonic coelom develop?
From the junction point the extra-embryonic mesoderm migration out form the junction between epiblast and hypoblasts it then positions itself under the cellular trophoblasts and begins surrounding the embryo as it forms it undergoes cavitation (creates cavities) which fill with fluid, the cavities then combine and grow forming a large continuous extra-embryonic coelom surrounding the entire embryo
What is the extra-embryonic mesoderm that connects the inside and outside layers together? What does it develop into?
A mesodermal stalk Develops into the umbilical cord
What is the function of the mesodermal stalk?
Attaches onto the embryo on the inside connecting it to the outside
By the end of gastrulation, what is the three layered embryo surrounded by?
The amniotic cavity, the yolk sac and extra-embryonic coelom
What separates the inner and outer balls of the embryo?
The extra-embryonic coelom
What layers of the uterus are digested away to allow the blastocyst to imbed itself in the uterus?
The epithelium then the extra-cellular matrix
Once the embryo is implanted in the uterus, what is the endometrium (epithelial layer of the uterus) called?
Decidua
What is secreted by the embryo in order to prevent menstruations? What does this allow by doing what? What kind of cells are secreting this?
Human chorionic ganadotrohpin (hCG) Allows pregnancy to continue by preventing menstruations Trophoblasts
How does the early embryo extract nutrients from the mother? How was the embryo getting nutrients before depending on the mother?
Digests the epithelium of the blood vessels which then pool in the lacunae, here the nutrients in the mothers blood are diffused into the embryo Before extracting nutrients from the mother the embryo was dependent on the yolk sac
The embryo imbeds what part of itself into the mothers uterus? What surrounds the entire embryo?
It become entirely imbedded in the uterus (known at this point as decidua FYI) It is surrounded by syncytial trophoblasts
What are the three layers that make the outer wall of the embryo? What is the origin of these tissues? What is the collective name for them?
Syncytial trophoblasts, cellular trophoblasts and extra-embryonic mesoderm Embryonic origin Chorion
What does the chorion combine with to form what important structure involved in nutrient and waste exchange for the embryo?
Decidua basalis The placenta
Label the following diagram What is being developed in this series of diagrams?
A chorionic villus (from primary chorionic villus in diagram 2 up to tertiary chorionic villus in diagram 4)
At secondary chorionic villus, why do blood vessels need to be developed?
The chorionic villus is too large to sufficiently gather nutrients from the lacuna just by passive diffusion, requires blood vessels
What changes occur between the secondary and tertiary chorionic villus?
The extra-embryonic mesoderm gives rise to fatal capillaries The cellular trophoblasts become reduced
Why does the cellular trophoblasts undergo its particular changes between secondary and tertiary villus structures?
Reduces the number of layers which the nutrients and waste need to diffuse through to go from blood capillaries to lacuna
Explain the structure and position of the fetal capillaries. What makes this advantageous for its function?
It is a single layer of squamous endothelium cells, located on the wall of the syncytial trophoblasts Makes diffusion very easy as it is very close to the lacuna
What do the tributary and branch of umbilical vein and artery connect to?
The embryonic heart via the umbilical cord
Why do the chrorionic villi form?
To increase the surface area that is exposed to the maternal blood in the lacunae
What is the function of the amniotic sac? What is it filled with?
Protects the embryo, allows it to move around and prevents it from dehydrating Amniotic fluid
The yolk sac in avian/reptiles is large and nutritious. In mammals it is neither, why is this? What is its function in mammals?
In mammals the embryo establishes a circulation with the mother early on to extract nutrients so doesn’t need to store it itself It does however provide nutrition for the very early stages of embryonic development before a circulation is established, also contains precursors for blood cells and produces cell stoa form the embryos primordial cells for the reproductive systems
What is the allantois in avians/reptiles and mammals?
Avians/reptiles = membranous sac which is used to store nitrogenous wastes and to transport O2 and CO2 in/out of the egg Mammals = forms part of the stalk of the extra-embryonic mesoderm and contributes the formation of the umbilical cord
What happens to the left umbilical artery as the embryo develops? Why?
It loses its connection to the heart and instead carrier blood to the developing liver Allows for the embryo to metabolise the rich nutrients that are taken up in the placenta
Why does the lacunae form the chorionic villi?
In order to increase the surface area exposed to the mothers blood
Label the diagram and indicate what the quality of blood going through each blood vessel is
