Fetal Circulation

1. Fetal
Circulation
Dr AmbikaJawalkar

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 30th
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”