Fetal Circulation

Objectives Discuss anatomy and physiology of fetal circulation Compare and contrast fetal circulation to infant circulation Define specialized structures of fetal circulation

Anatomy and Physiology Fetal Circulation Umbilical cord 2 umbilical arteries: return non-oxygenated blood, fecal waste, CO2 to placenta 1umbilical vein: brings oxygenated blood and nutrients to the fetus

Anatomy and Physiology Fetus depends on placenta to meet O2 needs while organs continue formation Oxygenated blood flows from the placenta To the fetus via the umbilical vein After reaching fetus the blood flows through the inferior vena cava

A/P Fetal Circulation Blood continues to travel from the inferior vena cava to the ductus venosis Ductus Venosis Small amount of blood routed to growing liver Increased blood flow leads to large liver in newborns

A/P Fetal Circulation Blood continues to travel up the inferior vena cava Empties into the right atrium of the heart The blood then passes to the left atrium through the foramen ovale

A/P Fetal Circulation Foramen ovale Small opening in the septum of the heart Completely bypasses the non-functioning lungs Blood continues journey to the left ventricle blood is then pumped into the aorta Blood is circulated to the upper extremities Blood then returns to the right atrium

A/P Fetal Circulation From the right atrium, the blood goes to the right ventricle then to the pulmonary arteries Pulmonary arteries Small amount goes to the maturing lungs Rest of blood is shunted away from lungs by ductous ateriosus back to aorta

A/P Fetal Circulation Blood travels back from aorta to the two umbilical arteries to the placenta The placenta will re-supply the blood with oxygen Fetal circulation is a low-pressure system

A/P Fetal Circulation Low pressure system Lungs are closed Most oxygenated blood flows between the atria of the heart through the foramen ovale This oxygen rich blood flows to the brain through the ductus arteriosus

Conversion of Fetal to Infant Circulation At birth Clamping the cord shuts down low-pressure system Increased atmospheric pressure(increased systemic vascular resistance) causes lungs to inflate with oxygen Lungs now become a low-pressure system Pressure from increased blood flow

Conversion: Fetal to Infant Circulation In the left side of the heart causes the foramen ovale to close More heavily oxygenated blood passing by the ductus arteriosus causes it constrict Functional closure of the foramen ovale and ductus arteriosus occurs soon after birth Overall anatomic changes are not complete for weeks

Conversion (cont) What happens to these special structures after birth? Umbilical arteries atrophy Umbilical vein becomes part of the fibrous support ligament for the liver The foramen ovale, ductus arteriosus, ductus venosus atrophy and become fibrous ligaments

Overview of Conversion Umbilical cord is clamped Loose placenta Closure of ductus venosus Blood is transported to liver and portal system Loss of placenta also leads to

Overview of Conversion First breath Lungs expand and fluid is expelled Decreased pulmonary resistance Increased pressure in left atrium Closure of foramen ovale

Overview of Conversion Loss of placenta Increased systemic resistance Pressure in right atrium decreased Change from right to left shunting to left to right blood flow Increased O2 levels in pulmonary circulation Closure of the ductus arteriosus

Fetal vs. Infant Circulation Low pressure system Right to left shunting Lungs non-functional Increased pulmonary resistance Decreased systemic resistance Infant High pressure system Left to right blood flow Lungs functional Decreased pulmonary resistance Increased systemic resistance

Summary Reviewed anatomy and physiology of fetal circulation Discussed conversion from fetal to infant circulation Compared fetal to infant circulation Determined outcome of special features associated with fetal circulation after birth