Fetal Circulation Dr.(Mrs.)S.Valliammal Lecturer College of Nursing NIMHANS Bangalore
Anatomy and Physiology Fetal Circulation Umbilical cord 2 umbilical arteries: return de- oxygenated blood, fecal waste, CO2 to placenta 1umbilical vein: brings oxygenated blood and nutrients to the fetus
Special Structures in Fetal Circulation Placenta – Where gas exchange takes place during fetal .life Umbilical Arteries – Carry deoxygenated blood from the fetus to placenta Umbilical Vein – Brings oxygenated blood coming from the placenta to the fetus Foramen Ovale – Connects the left and right atrium. It pushes blood from the right atrium to the left atrium. Ductus Venosus - Carry oxygenated blood from umbilical vein to inferior vena cava, bypassing fetal liver Ductus Arteriosus - Carry oxygenated blood from pulmonary artery to aorta, bypassing fetal lungs.
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 theblood flows through theinferior vena cava
Fetal Circulation Blood continues to travel to the inferior vena cava from the ductus venosus Ductus Venosus Small amount of blood routed to growing liver Increased blood flow leads to large liver in newborns
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
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
Fetal Circulation From the right atrium, the blood goes to the right ventricle then to the pulmonary arteries Pulmonary arteries Small amount of blood goes to the maturing lungs Rest of blood is shunted away from lungs by ductous ateriosus back to aorta
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
Why more blood flow directly to the Left atrium? Due to the higher pressure of the blood in the inferior vena cava, more blood flows from it directly into the left atrium via the foramen ovale. foramen ovale opens like a valve and can direct the blood stream that comes from below directly into the left atrium. the diameters of the inferior and superior vena cava are larger than that of the foramen ovale and therefore a small portion of the blood seeps into the right ventricle via the tricuspid valve. The heart is filled only with a mixed blood.
Fetal Circulation Low pressure system Lungs are closed Most oxygenated blood flows between the atria of the heart through the foramen ovale
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 Contd….
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 Contd….
Loss of placenta also leads to : First breath Lungs expand and fluid is expelled Decreased pulmonary resistance Increased pressure in left atrium Closure of foramen ovale Contd….
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 Contd….
Fetal vs. Infant Circulation Fetal Infant Low pressure system High pressure system Right to left shunting Left to right blood flow Lungs non-functional Lungs functional Increased pulmonary Decreased pulmonary resistance resistance Decreased systemic Increased systemic resistance resistance
Conclusion Oxygenated blood enters the umbilical vein from the placenta Enters ductus venosus Passes through inferior venacava Enters the right atrium Enters the foramen ovale Goes to the left atrium Passes through left ventricle Flows to ascending aorta to supply nourishment to the brain and upper extremities Contd….
. Enters superior vena cava Goes to right atrium Enters the right ventricle Enters pulmonary artery with some blood going to the lungs to supply oxygen and nourishment Flows to ductus arteriosus Enters descending aorta ( some blood going to the lower extremeties) Enters hypogastric arteries Goes back to the placenta End