Fetal Circulation

Dr Ambika Jawalkar

• 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

• Umbilical cord 1umbilical vein: brings oxygenated

blood and nutrients to the fetus

2 umbilical arteries: return deoxygenated blood, fecal waste, CO2 to placenta

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

• 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

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)

• 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

• 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

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

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

Applied Physiology

• Arial Septal Defect

• Patent Ductus Arteriosus

• Tetralogy of Fallot

VSD, PS, RVH & Overriding of Aorta

Medicine is the study of “Physiology gone awry”