Utero-placental circulation
Volume of blood in mature placenta; 500ml
Volume of blood in intervillous space; 150ml
Blood flow in intervillous space; 500-600ml/minutes
Pressure in intervillous space;
During uterine contraction; 30-50mmHg
During uterine relaxation; 10-15mmHg
Pressure in supplying uterine artery; 70-80mmHg
Pressure in draining uterine vein; 8mmHg
Maternal circulation is circulation of maternal blood through intervillous space.
Arterial Circulation
120-200 spiral arteries open into intervillous space by piercing basal plate at numerous site.
Cytotrophoblastic invasion into spiral arteries 12 weeks of pregnancy.
Invasion of trophoblast between 12-16 weeks radial arteries within myometrium.
Spiral arteries converted into utero-placental arteries.
Arteries reaches intervillous spaces; this increases the blood flow.
Trophoblast cell that donot take part in villous structure called extravillous trophoblast (EVT).
Extravillous trophoblast (EVT) are;
1. Endovascular
Migrate into lumen of spiral arteries and replace endothelium.
2. Interstitial
Interstitial invades into myometrium.
Deeply invade into uterine wall.
NK cells prevent morbid adhesion of placenta.
(Placenta accreta); when placenta grow too deeply into uterine wall.
Defects in trophoblast invasion and failure to establish maternal circulation; lead to complication of pregnancy (pregnancy induced Hypertension, IUGR).
Venous Drainage
Venous blood of intervillous space drains through uterine veins which pierce basal palate.
Circulation in Intervillous Space
Arterial blood enters intervillous space; after reaches chorionic plate.
Villi help in mixing and slowing of blood flow.
Villi pulsation aided by uterine contraction help migration of blood toward basal plate to uterine vein.
Syncytial knot present in intravillous circulation.
Carried through maternal circulation to lung where disappear by lysis.
100,000 syncytial knots (syncytiotrophoblastic knots) circulate in maternal blood in 24 hours.
During uterine contraction veins are occluded but arterial blood is forced into intervillous space, while uterine relaxation facilitates venous drainage.
Blood in intervillous space is protected from cloting by fibrinolytic enzyme activity of trophoblast.
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