The Placenta Flashcards
Which cells of the blastocyst develop into the fetal membranes? In which week of embryology does this occur?
Synctiotrophoblast and Cytotrophoblast
Occurs in the week of 2’s
Which cells produce hcG?
Syncytiotrophoblast
How does communication between the endometrium and the conceptus start?
Syncytiotrophoblast cells being the communication with the endometrium at day 6 of pregnancy
What happens to the yolk sac, amniotic sac and chonrionic sac as the embryo grows?
- Yolk sac dissapears
- Amniotic sac enlarges
- Chorionic sav occupies by expanding amniotic sac
What are chorionic villi?
Projections from the trophoblast that establish an inital unit of exchange with the endometrium and anchor the placenta
Material blood vessels surround the villi to allow the exchange to occur
Distinguish between primary, secondary and tertiary villi?
- Primary villi - early finger like projections of trophoblast
- Secondary villi - invasion of mesenchyme into core
- Tertiary villi - invasion of mesenchyme core by fetal vessels
How does the barrier between fetal and maternal circulations change throughout pregnancy?
1st Trimester- thick barrier with a full layer and cytotrophoblast and syncytiotrophoblast
As pregnancy progesses → placental membrane becomes progessively thinner as the metabolic demands of the fetus increase
Eventually one layer of trophoblast separates maternal and fetal blood
What defects can occur in implantation?
- Implantation in the wrong place
- ectopic
- placenta praevia
-
Incomplete invasion
- placental insufficiency
- pre-eclampsia
Explain the main principles of ectopic pregnancies and placenta praevia
How is the implantation invasion controlled?
The Decidual reaction provides a balancing force for how far the trophoblast can invade
With regards to decidual reaction, why is ectopic pregnancy so dangerous?
There is no decidual reaction outside of the uterus, therefore in ectopic pregnancies invasion goes unchecked leading to haemorrhage
What happens if the decidual reaction is sub- optimal?
If invasion is not deep enough the pregnancy may not be maintained or there is a spectrum of placental insufficiency including pre-eclampsia
What blood vessles exist in the umbilical cord?
- 2 umbilical arteries - carry deoxygenated blood from fetus → placenta
- 1 umbilical vein - carries oxygenated blood from placenta → fetus
What hormones are produced by the placenta?
Protein hormones:
- hCG
- human chorionic somatomammotrophin
- human chorionic thyrotrophin
- human chorionic corticotrophin
Steroid hormones:
- progesterone
- oestrogen
What is the function of Human Chorionic Gonadotrophin (hCG) and where is it produced?
- Produced by the syncytiotrophoblast in the 1st 2 months of pregnancy
- Supports the secretory function of the corpus luteum in the 1st trimester
Why does the placenta produce steroid hormone?
Placenta secretes oestrogen and progesterone
Maintains the pregnancy state → takes over production from the corpus luteum at week 11
How can placental hormones influence maternal metabolism?
- Progesterone → increases appetite to lay down fat stores
- hCS/ hPL → makes mother insulin resistant to increase glucose available for the fetus
How do molecules move across the placenta?
- Mostly by simple diffusion: water, electrolytes, urea & uric acid and gases
- Glucose moved by facilitated diffusion
- Active transport: amino acids, iron, vitamins
How is gas exchange limited across the placenta?
Flow limited, not diffusion limited
Therefore adequate flow is essential to maintain fetal O2 stores
Which class of maternal antibodies can diffuse across the placenta?
IgG only
Transported by receptor mediated endocytosis
Which harmful substances can cross the placenta?
- Thalidomide
- Alcohol
- Therapeutic drugs: anti-epileptic, Warfarin, ACE inhibitors
- Drugs of abuse
- Maternal smoking
At which stage in embryological development is teratogenesis the most harmful?
Weeks 3-8, in the embryonic stage
Events less severe from weeks 9 onwards
