Fetal Circulation By Sanjeev Anatomy and Physiology Fetal

Fetal Circulation By : Sanjeev

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

Anatomy and Physiology Fetus depends on placenta to meet O 2 needs while organs continue formation n Oxygenated blood flows from the placenta to the fetus via the umbilical vein n

After reaching fetus the blood flows through the inferior vena cava

A/P Fetal Circulation Blood continues to travel to the inferior vena cava from the ductus venosus n Ductus Venosus n ¨ 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 n Empties into the right atrium of the heart n The blood then passes to the left atrium through the foramen ovale n

A/P Fetal Circulation n Foramen ovale ¨ Small opening in the septum of the heart ¨ Completely bypasses the non-functioning lungs n n n 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 n Pulmonary arteries n ¨ Small n 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 n The placenta will re-supply the blood with oxygen n Fetal circulation is a low-pressure system n

Why more blood flow directly to the Lt. atrium? n n 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 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.

A/P Fetal Circulation n 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 n 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) n 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 n Loose placenta n Closure of ductus venosus n Blood is transported to liver and portal system n

Overview of Conversion Loss of placenta also leads to : n First breath n Lungs expand fluid is expelled n Decreased pulmonary resistance n Increased pressure in left atrium n Closure of foramen ovale n

Overview of Conversion Loss of placenta n Increased systemic resistance n Pressure in right atrium decreased n Change from right to left shunting to left to right blood flow n Increased O 2 levels in pulmonary circulation n Closure of the ductus arteriosus n

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

n . n n n n 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 extremeties

n . n n n n 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

Special Structures in Fetal Circulation n Placenta – Where gas exchange takes place. during fetal life n Umbilical Arteries – Carry deoxygenated blood from the fetus to placenta n Umbilical Vein – Brings oxygenated blood coming from the placenta to the fetus n Foramen Ovale – Connects the left and right atrium. It pushes blood from the right atrium to the left atrium. n Ductus Venosus - Carry oxygenated blood from umbilical vein to inferior venacava, bypassing fetal liver n Ductus Arteriosus - Carry oxygenated blood from pulmonary artery to aorta, bypassing fetal lungs. n