Embryology weeks 1 and 2 Flashcards
Where is the oocyte fertilised by the sperm?
In the ampulla of the Fallopian tube
What is cleavage?
The first mitotic division of the zygote, resulting in 2 blastomeres
What is the zone pellucida
It is the glycoprotein ‘shell’ that one sperm will be successful in penetrating. It protects but also restricts growth
What is meant by the terms Totipotent, Pluripotent, Multipotent and Unipotent?
TOTIPOTENT cells have the ability to form any type of cell
PLURIPOTENT cells can become any type of cell except placenta cells
MULTIPOTENT cells can differentiate into a few different types opposite cell eg stem cells found in bone marrow can form red and whit blood cells
UNIPOTENT cells can only differentiate into one type of cell
What is PGD?
Pre-implantation genetic diagnosis means that a cell can be safely removed from the morula and tested for serious inheritable genetic diseases so that only healthy embryos are transferred into the uterus.
What happens in week 1 compaction?
First cavity forms
Blastocyst formation
What occurs in week 1 hatching?
Blastocyst hatches from zone pellucida so it is free to enlarge. It can now interact with the uterine surface to implant
What is the multinucleated sheet called that forms in week 2?
Synctiotrophoblast
What happens during compaction?
The 8 cell or 16 cell embryo changes shape to form the morula. The first cavity is formed during compaction- the blastocyst.
What is hatching and why must it occur?
It is when the blastocyst (an embryo pre-implantation day5/6) hatches from the zone pellucida meaning it is free to grow and can now interact with the uterin epithelium so implantation can occur
Where is the ideal site for implantation?
The posterior uterine wall
What happens during implantation?
The embryo breaches the uterine epithelium to interact with the uterine stroma. This means implantation is interstitial. Implantation establishes maternal blood flow to the placenta. It also establishes the basic structural unit of materno-fetal exchange- the chorionic villus
What does the trophoblast go on to form?
The outer cell mass which is split into
The Syncytiotrophoblast and the Cytotrophoblast
What makes up the bilaminar disk?
Epiblast
Hypoblast
Amniotic cavity
What does the epiblast go on to form?
The embryo
What does the extra embryonic reticulum do and then go on to form?
The acellular extra embryonic reticule pushes the primitive yolk sack away from the cytotrophblast
What are lacunae? Why are they important?
They are spaces in the syncytiotrophoblast formed when maternal sinusoids invade. This is when uteroplacental circulation begins
How is the secondary yolk sac formed?
The primary yolk sack pinches off and small segment becomes the secondary yolk sac
How is the chorionic cavity formed??
Spaces within the extraembryonic mesoderm merge to form a cavity known as the chorionic cavity
What is an ectopic pregnancy? Why can it be life-threatening?
When implantation occurs not In the uterine body most commonly in the Fallopian Tube. It can quickly become life threatening as the Fallopian tube could rupture causing internal bleeding
What is placenta praevia?
Implantation in the lower uterine segment. The placenta blocks the birth canal so c section is necessary. It can become life threatening
