Implantation To Gastrulation Flashcards
Which are the three initial structures of blastocyst before implantation?
- Trophoblast or trophectoderm
- Blastocoel
- Inner cell mass or embryoblast
What happens when implantation begins?
The hatched blastocyst attaches to the endometrial layer of the uterus
At day 8 the blastocyst is partially embedded in the endometrial stroma.
In what orientation does blastocyst attach to endometrium
The embryo implants into the uterine wall with the inner cell mass towards the uterine wall
What happens to the trophoblast portion closest to the inner cell mass upon implantation?
Which structures does it give rise to?
The trophoblast over the embryoblast differentiates into two structures:
- Cytotrophoblast
- Syncytiotrophoblast
Describe syncytiotrophoblast
Multinucleated zone
No distinct cell boundaries
Distinguish between cytotrophoblast from syncytiotrophoblast in terms of cell division.
Cytotrophoblast contain mitotic figures, hence they can divide.
Mitotic figure not present in syncytiotrophoblast.
How does syncytiotrophoblast grow in the absence of mitotic figures?
Cells in the cytotrophoblast divide and migrate into syncytiotrophoblast.
Then these cells lose their individual cell membranes and fuse with the syncytiotrophoblast.
What happens to the cells of the inner cell mass upon implantation?
Cells of the inner cell mass differentiate into two structures:
- Hypoblast layer
- Epiblast layer
Hypoblast
Layer of small cuboidal cells.
Adjacent to the blastocyst cavity.
Epiblast
Layer f high columnar cells.
Adjacent to amniotic cavity (precursor area- cytotrophoblast in contact with uterine wall at the beginning of implantation)
Explain the formation of the amniotic cavity.
Formation of the amniotic cavity begins at the same time as the inner cell mass begins differentiating into epiblast and hypoblast.
A small cavity begins to appear within the epiblast, separating the epiblast from the cytotrophoblast adjacent to the uterine wall.
What happens to the conceptus as time progresses?
The conceptus invades deeper in the endometrium.
How does the epiblast contribute to formation of amniotic cavity?
Cells of the epiblast extend around the cytotrophoblast to form the amniotic cavity.
Upon formation of the amniotic cavity, the epiblast can be divided into two parts. Which are these parts?
- Epiblast- integrated into the bilaminar embryo.
2. Amniotic ectoderm- adjacent to cytotrophoblast.
Where do primordial germ cells originate from?
Primordial germ cells derive from the epiblast.
They are induced in the epiblast at the edge that will give rise to the future posterior of the embryo.
Explain the formation of the yolk sac.
The hypoblast extends to surround the cytotrophoblast, forming the yolk sac cavity.
What is the bilaminar embryo?
Bilaminar structure between the amniotic cavity and yolk sac cavity.
Formed by epiblast and hypoblast.
Describe the fun structure of the conceptus by the end of day 8.
The amniotic ectoderm completely surrounds the amniotic cavity over the epiblast.
The yolk sac endoderm completely surrounds the yolk sac cavity over the hypoblast.
Conceptus completely embedded in endometrium.
The syncytiotrophoblast surround the entire conceptus.
What happens to the primordial germ cells by the end of day 8, when yolk sac cavity is completely formed?
Primordial germ cels migrate into the yolk sac endoderm.
Trophoblastic lacunae
Spaces in the syncytiotrophoblast.
Filled with maternal blood and gland secretions.
How are trophoblastic lacunae filed with maternal blood?
Maternal endometrium is fried with sinusoids- enlarged maternal capillaries which are congested.
Cells of the syncytiotrophoblast penetrate deeper into the stroma and erode the endothelial lining of the maternal capillaries.
The syncytial lacunae become continuous with the sinusoids, and maternal blood enter the lacunae system.
Extraembryonic Mesoderm
Formed by a anew population of cells.
Arise between the inner surface of the cytotrophoblast and the outer surface of the yolk sac endoderm.
Then line the entire inner surface of cytotrophoblast.
Arise perhaps from yolk sac cells or cytotrophoblast.
Chorionic Cavity
Forms as a space in the extraembryonic mesoderm.
Expands to generate connecting stalls.
Amniotic cavity expands after to obliterate most of the chorionic cavity.
Which structures from the amnion?
Amniotic ectoderm.
Extraembryonic mesoderm.
Which structures form the bilaminar embryo?
Epiblast
Hypoblast
Which structures form the yolk sac?
Yolk sac endoderm.
Extraembryonic mesoderm.
Extraembryonic Mesoderm
Formed by a anew population of cells.
Arise between the inner surface of the cytotrophoblast and the outer surface of the yolk sac endoderm.
Then line the entire inner surface of cytotrophoblast.
Arise perhaps from yolk sac cells or cytotrophoblast.
Chorionic Cavity
Forms as a space in the extraembryonic mesoderm.
Expands to generate connecting stalls.
Amniotic cavity expands after to obliterate most of the chorionic cavity.
Which structures from the amnion?
Amniotic ectoderm.
Extraembryonic mesoderm.
Which structures form the bilaminar embryo?
Epiblast
Hypoblast
Which structures form the yolk sac?
Yolk sac endoderm.
Extraembryonic mesoderm.
What percentage of pregnancies are twin pregnancies?
30%
What are fraternal twins?
Fraternal or dizygotic twins arise from polyovulation in the same cycle.
Explain sharing of amnion, chorion and placenta in fraternal twins.
Almost all have their own amnion, chorion and placenta.
What are monozygotic twins?
Twins that raze from fertilization of the same egg.
Explain shaving of amnion,placenta and chorion in monozygotic twins
25% are dichorionic- splitting at 2 cell stage (1-3 days)
75% are monochorinic- splitting in early blastocyst (4-9 days)
5% are monoamniotic and monochorionic- splitting in late blastcyst (9 days)
Ectopic Pregnancy
Implantation in sits other than the uterus.
Implantation in the Fallopian tubes accounts for more than 90% of ectopic pregnancies.
Other sites include: cervix; ovary; abdominal membranes.
Incidence of ectopic pregnancies.
1 in 200
Twin- Twin Transfusion Syndrome (TTTS)
Caused by anastomoses of chorionic vasculatures
Lead to imbalanced blood flow in the twins, with one having to much and one having too little.
What is the incidence of TTTS
20%
How can survival of TTTS twins be achieved?
Ablating anastomoses with lase.
