Placental blood supply
= 500-750 mL/min @ term
* 85% goes to placenta
Blood supply to uterus is by uterine and ovarian arteries
--> Arcuate arteries
--> Radial arteries (Penetrating the myometrium)
--> Spiral arteries, and basal arteries
Spiral arteries supply the intervillous space
Basal arteries supply the myometrium and decidua
Blood in intervillous space bathes the chorionic villi
Chorionic villi have 2 layers of cells
* Syncytiotrophoblasts (on the maternal side)
* Cytotrophoblasts (on the foetal side)
Placental blood flow is not autoregulated
* Pressure dependent
Foetal [Hb] at birth = 17-18g/dL
Typical values of pO2 and pCO2
[KB2:p253]
Maternal
Uterine artery
pO2 = 100 mmHg (SatO2 = 98%)
pCO2 = 32 mmHg
Uterine vein
pO2 = 40 mmHg (SatO2 = 75%)
pCO2 = ??45 mmHg
Foetal
Umbilical artery
pO2 = 18 mmHg (SatO2 = 45%)
pCO2 = 55 mmHg
Umbilical vein
pO2 = 28 mmHg (SatO2 = 70%)
pCO2 = 40 mmHg
Placental oxygen consumption
= 10 mL/kg/min
= 1 mL/100g/min
= 5 mL/min
Placental blood flow ~ 600mL/min
Umbilical blood flow ~ 300mL/min
Surface area for gas exchange = 12 to 16 square meter