Placenta Flashcards
When does the placenta start developing?
2nd week of development
What is week 2 of development also known as?
‘Week of 2s’
What happens in week 2?
Two distinct cellular layers emerge
Outer cell mass
- syncytiotrophoblast
- cytotrophoblast
Inner cell mass - becomes bilaminar disk
- ephiblast
- hypoblast
When does implantation begin?
Day 6
What happens by the end of the 2nd week?
Conceptus has mechanically implanted
Embryo and its cavities are suspended by the connecting stalk to the chorionic cavity
What are the 2 cavities?
Amniotic cavity
Yolk sac
What happens to the yolk sac?
Disappears
What happens to the amniotic sac?
Enlarges to surround foetus
What happens to the chorionic sac?
Occupied by expanding amniotic sac
What does implantation achieve?
Establishes basic unit of exchange
- primary villi
- secondary villi
- tertiary villi
Anchors placenta
Establish maternal blood floe within the placenta
What are primary villi?
Early finger-like projections of trophoblast
What are secondary villi?
Invasion of mesenchyme into core
What are tertiary villi?
Invasion of mesenchyme core by foetal vessels
What separates maternal blood from the foetal capillary wall?
One layer of trophoblast
What is a chorionic villus?
Finger like projections of trophoblast that are in the inner connective tissue core of the placenta and
Maximise surface area for foetal blood flow - contain small blood vessels
What implantation defects may occur?
Ectopic pregnancy Placenta praevia Placenta accreta Placental insufficiency Pre-eclampsia
What is an ectopic pregnancy?
Implantation of embryo at site other than the uterus
What is placenta praevia?
Implantation in the lower uterine segment
- can block cervix
- can require a c section
What controls the level of invasion in implantation?
In the presence of a conceptus - endometrium transforms into the decidua
The decidual reaction provides the balancing force for the invasive force of the trophoblast
What is placenta accreta?
Placenta invades too deep
Insufficient decidual reaction
What is placental insufficiency?
Inadequate blood flow to the placenta
What is pre-eclampsia?
Maternal high blood pressure caused by insufficient invasion by the placenta
How does the structure of the chorionic villus structure change during the pregnancy?
In first trimester - the villus has a thicker barrier
Third trimester - barrier is thinner as cytotrophoblast disappears
What are the vessels in the umbilical cord?
Two umbilical arteries
- deoxygenated blood from foetus to placenta
One umbilical vein
- oxygenation blood from placenta to foetus
