FETAL CIRCULATION

 

INTRODUCTION: The fetus depends upon the mother for oxygen and nutrients and for the removal of carbon dioxide an other waste products. The site of exchange between fetus and mother is the placenta, which contains fetal and maternal blood vessels that are very close to one another.

THE FETAL-MATERNAL BLOOD: The blood of the fetus does not mix with the blood of the mother; substances are exchanged by diffusion and active transport mechanisms. The fetus is connected to the placenta by the umbilical cord, which contains two umbilical arteries and one umbilical vein.

THE UMBILICAL CODE: The umbilical arteries are branches of the fetal internal iliac arteries; they carry blood from the fetus to the placenta. In the placenta, carbon dioxide and waste products in the fetal blood enter maternal circulation, and oxygen and nutrients from the mother’s blood enter fetal circulation. The umbilical vein carries this oxygenated blood from the placenta to the fetus. Within the body of the fetus, the umbilical vein branches: One branch takes some blood to the fetal liver, but most of the blood passes through the ductus venosus to the inferior vena cava, to the right atrium.

NEONATAL CIRCULATION: After birth, when the umbilical cord is cut, the remnants of these fetal vessels constrict and become nonfunctional. The other modifications of fetal circulation concern the fetal heart and. Because the fetal lungs are deflated and do not provide for gas exchange, blood is shunted away from the lungs and to the body. The foramen ovale is an opening in the interatrial septum that permits some blood to flow from the right atrium to the left atrium, not, as usual, to the right ventricle. The blood that does enter the right ventricle is pumped into the pulmonary artery. The ductus arteriosus is a short vessel that diverts most of the blood in the pulmonary artery to the aorta, to the body. Both the foramen ovale and the ductus arteriosus permit blood to bypass the fetal lungs. Just after birth, the baby breathes and expands its lungs, which pulls more blood into the pulmonary circulation. More blood then returns to the left atrium, and a flap on the left side of the foramen ovale is closed. The ductus arteriosus constricts, probably in response to the higher oxygen content of the blood, and pulmonary circulation becomes fully functional within a few days.

RELATED;

1.  FETAL DIAGNOSIS

2.  HEMORRHAGIC DISEASE OF THE NEW BORN

3.  ANATOMY AND PHYSIOLOGY

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