Fetal circulation

Fetal Circulation

1. Fetal
Circulation
Dr Ambika Jawalkar

2. •Fetal lungs are functionally
inactive & fetus derives O2 &
nutrients from placenta
•Fetus receives blood from
placenta through umbilical vein
which is only 80% saturated as
placenta has extracted some O2

3. •Umbilical cord
 1umbilical vein: brings oxygenated
blood and nutrients to the fetus
2 umbilical arteries: return
deoxygenated blood, fecal waste,
CO2 to placenta

4. Diagram of a section through the human placenta, showing the
way the fetal villi project into the maternal sinuses.

5. •Parallel arrangement of two main
arterial systems and their
respective ventricles.
•High resistance and low flow of
pulmonary circulation.
•Low resistance and high flow of
placental circulation.
•Presence of shunts.
Characteristics of fetal
circulatory dynamics

6. Shunts in fetal circulation
•Ductus venosus (between
umbilical vein & fetal IVC)
•Foramen ovale (between RA & LA)
•Ductus arteriosus or aortic
isthmus (between pulmonary
artery & aorta)

7. •From umbilical vein blood enters
liver of fetus & some amount
bypasses liver & enters IVC through
ductus venosus
•IVC drains into RA
•50% of blood from RA enters LA
through Foramen ovale
•Another 50% enters RV from there
into pulmonary artery
•But fetal lungs are collapsed

8. •So only small amount of blood
reaches LA through pulmonary
veins
•The main bulk of blood from RV
enters aorta through ductus
arteriosus
•Blood from aorta is then distributed
to the whole body
•2 umbilical arteries which arise
from fetal aorta transport blood to
placenta for oxygenation

12. Why HbF ??
•O2 saturation of fetal arterial blood
is much lower than in adults
•Fetal tissues are highly resistant to
effect of hypoxia
•Baro & chemoreceptor reflexes
develop at about 30
th
week of
intrauterine life

13. Changes occurring at birth
•Closure of umbilical veins
•Closure of ductus venosus
•Expansion of lungs
•As lungs fill with air
pulmonary vascular resistance
decreases
•Closure of foramen ovale
cause of change in pressure
gradient between atria

15. Applied Physiology
•Arial Septal Defect
•Patent Ductus Arteriosus
•Tetralogy of Fallot
VSD, PS, RVH & Overriding of
Aorta

16. Medicine is the study of
“Physiology gone awry”