Placenta Flashcards
What is the placenta?
Highly specialized
Haemo-chorial organ of pregnancy
Formed from fetal tissue (chorion frondosum) and maternal tissue (decidua basalis)
Support normal growth and development of the fetus
Describe the structure of the placenta?
Discoid shape Diameter 15-25 cm Thickness 3 cm Weight 500 - 600 g 15-20 Cotyledons on maternal side
Fetal part = chorionic plate (frondosum)
Maternal part = decidual plate (basalis)
When does the placenta gain full function?
12 weeks of gestation
What are the clinical problems associated with abnormal placenta?
IUGR Previa Abruption Pre eclampsia Accreta intreata and percreta HDFN
What are the clinical problems of the umbilical cord?
Cord around the neck
True knots
Velamentous insertion and vasa previa
Absent umbilical artery
What are the events necessary for formation of the placenta?
Implantation
Placentation
Utero-placental circulation
Modification of maternal physiology
What is implantation?
Fixing of a hatched blastocyst
In the receptive endometrium
(Within 6 days after fertilization)
To form a physical and functional contact with the uterus
What is placentation?
Trophoblastic invasion of the stratum spongiosum and uterine spiral arteries to establish utero-placental circulation
By villous pathway (syncytiotrophoblast)
By extra-villous pathway (endovascular and interstitial cytotrophoblast)
Endovascular -> endothelium
Interstitial-> tunica media
What is decidualization of the endometrium?
Progesterone from the corpus luteum
Causes formation of secretory endometrium
Packing the stroma with glycogen and protein for fetal nutrition
Until uterine-placental circulation is established
When does the placenta take over progesterone synthesis from corpus luteum?
POA 8 weeks (6 weeks gestation)
What is the function of betaHCG?
Secretion of beta HCG by syncytiotrophoblast to save corpus luteum’s progesterone production, thus stopping menstruation
When is the utero-placental circulation established?
POA 3rd week by vasculogenesis and angiogenesis
But fully established at POA 12 th week
Placenta is now fully developed
When is the placenta fully developed?
POA 12th week
Why is the fetal allograft not rejected by maternal immune system?
Maternal immune system shifts towards humoral»_space; cell mediated
Trophoblast do not express MHC I & II
