Embryology Flashcards
(24 cards)
What is the blastocyte composed of?
Embryoblast
Trophoblast
What does the trophoblast differentiate into?
Cytotrophoblast
Synctiotrophoblast
What does the embryoblast differentiate into?
Hypoblast
Epiblast
The blastocyte is a foreign body. Why doesn’t the mother’s immune system attack?
The syncytiotrophoblasts become multinucleated (have multiple nuclei in each cell).
This makes the gaps between the cells very small, so immune response cells cannot reach the blastocyte.
Chemicals are also secreted which deter the immune system.
What is the significance of the blastocyte becoming bilaminar?
First stage of the body plan being organised.
Epiblast forms dorsal surface of embryo (back).
Hypoblast forms the ventral surface (front).
How is the amniotic cavity formed?
This fluid-filled cavity forms in the epiblast layer as the two layers separate further.
At the stage of full implantation, what does the blastocyte look like?
Coagulation plug forms at the surface of lining.
Hypoblast cells migrate and line the blastocyte cavity to form a primary yolk sac.
The blastocyte grows and gets closer to a maternal capillary.
There is no placental circulation when the embryoblast is implanted in the uterus lining.
How does the developing embryoblast receive nutrients?
Uteroplacental circulation is set up:
Syncytiotrophoblasts degrade a maternal capillary wall to set up circulation.
This can cause some bleeding which can be confused with a period.
What is the name of the layer which forms between the primary yolk sac and the cytotrophoblast, and eventually covers the amniotic cavity too?
Extraembryonic mesoderm layer
Where does the Chorionic cavity form?
Extraembryonic mesoderm
What happens to the primary yolk sac?
Primary yolk sac is pushed away and degraded as the Secondary (definitive) yolk sac forms due to hypoblasts migrating.
By the end of week 2, where are the amniotic cavity and secondary yolk positioned?
They are suspended in the chorionic cavity by a connecting stalk (this will go onto form the umbilical cord later).
Which layer is composed of multinucleated cells?
Syncytiotrophoblast
Which layer must the sperm penetrate to fertilise the oocyte?
Zona pellucida
What is initially formed when a sperm fertilises an oocyte?
Zygote
What is the name of the outer layer of cells of the blastocyst that will take part in the formation of the placenta?
Trophoblast
What do pregnancy tests use as an indicator of pregnancy?
human chorionic gonadotrophin (hCG)
What is an ectopic pregnancy?
Implantation of an embryo in an abnormal site (outside of uterus).
Occurs in ovary, ampulla, uterine tube, cervix, abdomen
What happens if the embryo is implanted near the cervix?
Placenta forms over the cervix.
This can cause severe bleeding later on in the pregnancy when the weight of the foetus ruptures vessels in the cervix.
C-section is needed.
What happens if the embryo is implanted in the uterine tube?
Uterine tube isn’t elastic like the uterus, so it ruptures as the foetus grows.
In abdominal implantation, the fertilised egg develops between the rectum & uterus (rectouterine space).
Lithopeadion can arise as a result. What is this?
‘Stone child’
Foetus dies in the abdomen, but is too large to be reabsorbed.
So it calcifies instead.
This protects the mother from the necrotic tissue (dead tissue) of the foetus.
How does a hydatidiform mole form?
What result would a pregnancy test show?
Fertilisation of an egg with no nucleus.
This results in the development of the trophoblast without any embryonic tissue.
Syncytiotrophoblasts would still produce hCG, therefore giving a false positive result.
What does the primitive streak consist of?
- Primitive pit
- Primitive node
- Primitive groove
The disruption of the left/right axis causes a condition called situs inversus.
What does this cause?
Organs are mirrored/reversed from their original positions.
This leads to problems when only some organs are mirrored, which results in abnormal connections between organs.
