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
What hormones are produced by the placenta?
Protein hormones
- human chorionic gonadotrophin
- human chorionic somatomammotrophin
- human chorionic thyrotrophin
- human chorionic corticotrophin
Steroid hormones
- progesterone
- oestrogen
Why does the placenta produce steroid hormones?
Takes over from the corpus luteum in the 11th week
Where is human chorionic gonadotrophin produced?
Syncytiotrophoblast
What is the role of human chorionic gonadotrophin?
Supports secretory function of corpus luteum
When is human chorionic gonadotrophin produced?
First 2 months of pregnancy
What is the role of human chorionic somatomammotrophin?
Regulating metabolism in pregnant women - increases glucose availability to foetus
What is the role of human chorionic thyrotrophin?
Acts similar to TSH
What is the role of human chorionic corticotrophin?
Acts similar to ACTH
What are the roles of the placental steroid hormones?
Maintaining pregnant state
Progesterone - increases maternal appetite
What are the transport functions of the placenta?
Simple diffusion
- water
- electrolytes
- urea
- gases
Facilitated diffusion
- glucose
Active transport - transporters in syncytiotrophoblast
- amino acids
- iron
- vitamins
How is passive immunity transferred?
IgG transferred across placenta via a receptor mediated process
What harmful substances can cross the placenta?
Thalidomide
Alcohol
Illegal drugs
Smoking contents
Drugs
- anti-epiletpics
- warfarin
- ACEi
WHat are the effects of alcohol crossing the placenta?
FAS - foetal alcohol syndrome
ARND - alcohol related neurodevelopmental disorder
