Placental circulation
Total blood volume in Placenta; 500ml
Placental circulation; two separate circulatory system for blood.
1. Maternal placental blood circulation
(Utero-placental circulation)
2. Fetal-placental blood circulation
(Fetal-placental circulation)
1. 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.
2. Feto-placental circulation
Blood vessel enter chorionic plate underneath amnion.
2 Umbilical arteries
1 Umbilical vein
2 Umbilical arteries carry impure blood from fetus.
1 Umbilical vein carry oxygenated blood to fetus.
Three shunt in fetal circulation
Constrict after birth.
1. Ductus arteriosus
Connecting pulmonary artery with descending aorta, bypass pulmonary circulation.
Close first 72 hours after birth.
2. Ductus venous
Fetal blood vessel connecting umbilical vein to IVC (inferior vena cava).
3. Foramen ovale
Shunts highly oxygenated blood from right atrium to left atrium (most oxygenated blood).
Ductus venous - through IVC - Right atrium - through foramen ovale - left atrium
Oxygenated rich red blood cell get from placenta to fetal tissue.
Blood from placenta highly oxygenated, color red.
From the placenta, oxygenated blood get through umbilical vein carried oxygenated blood towards liver.
When umbilical vein reaches the liver, bypass liver from shunt ductus venous towards oxygenated blood inferior vena cava(IVC).
Oxygenated blood reaches right atrium via IVC and enter left atrium via patent foramen ovale.
Rich oxygen blood go from right atrium to left atrium then left ventricle.
And left ventricle to aorta, by pass lung and send to systemic circulation and leave poor oxygenated blood through umbilical arteries and get back to placenta to pick up oxygen.
(Very little less oxygenated blood mix with oxygenated blood).
Poor blood return to right atrium through superior venacava.
Less oxygenated blood pumped from right ventricle into left pulmonary artery.
Less oxygenated blood shunted through ductus arteriosus to descending aorta.
Then enters the umbilical cord and flow into placenta.
In placenta CO2 and waste product released.
Fetal blood flow through placenta; 400ml per minute
Pressure in umbilical artery; 60mmHg
Pressure in umbilical vein; 10mmHg
Fetal capillary pressure in villi; 20-40mmHg
Umbilical artery Umbilical vein
O2 saturation 50-60% 70-80%
PCO2 20-25mmHg 30-40mmHg
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