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