FETAL CIRCULATIONPresented by:A.Priyadharshini M.Sc(N),Lecturer,Jai institute of nursing andresearch,Gwalior.
INTRODUCTION:• The key to understand the fetal circulation is the fact that oxygen is derived from the placenta!• In addition the placenta is the source of nutrition and the site of elimination of waste.
Umbilical vein: This vein leads from the umbilicalcord to the underside of the liverand carries blood rich in oxygen andnutrients. It has a branch and joinsthe portal vein and supplies the liver.
The ductus venosus: (from a vein to vein) This connects the umbilical vein tothe inferior venacava. At this pointthe blood mixes with thedeoxygenated blood returning fromthe lower parts of the body. Thusthe blood throughout the body is atbest partially oxygenated.
The foramen ovale: ( oval opening) This is a temporary openingbetween the atria that allows themajority of blood entering from theinferior venacava to pass across intothe left atrium. The reason for thisdiversion is that the blood does notneed to pass through the lungs tocollect oxygen.
The ductus arteriosus( from artery to artery) This leads from the bifurcation ofthe pulmonary artery to thedescending aorta, entering it justbeyond the joint point where thesubclavian and carotid arteries leave.
Umbilical arteries: These branch off from the internaliliac arteries and become theumbilical arteries when they enterthe umbilical cord. They return bloodto the placenta.
The circulatory process:• The blood takes about half a minute to circulate.• From the placenta, blood passes along the umbilical vein through the abdominal wall to the under surface of the liver. This is the only vessel in the fetus that carries unmixed blood.
• The ductus venosus carries blood to the inferior venacava where it mixes with the blood from the lower body.• From here the blood passes into the right atrium and most of it is directed across through the foramen ovale into the left atrium.• Following its normal route it enters into the left ventricle and passes into the aorta.
• The heart and brain receives a supply of relatively high oxygenated blood since the coronary and carotid arteries are earlier branches of aorta.• The arms also benefit via the subclavian arteries. Arms are well developed for this reason.
• Blood collected from the upper parts of the body returns to the right atrium in the superior venacavaa. This blood is depleted of oxygen and nutrients.• This stream of blood crosses the stream entering from the inferior venacava and passes into the right ventricle.
• The two streams remain separate because of the shape of the atrium but there is a mixing of 25% of the blood, allowing a little oxygen and nutrients to be taken into the lungs through the pulmonary artery. This is necessary for the lung development.
• The remainder blood passes through the ductus arteriosus to the aorta. Blood continues along the aorta and although low in oxygen, has sufficient to supply the remaining organs and legs.• The internal iliac arteries lead into the hypogastric arteries, which return blood to the placenta via the umbilical arteries.
• The remaining blood supplies the lower limbs and returns to the inferior venacava.