Introduction of Fetal Circulation

Before we proceed through fetal circulation, we should understand the many temporary structures that allow fetal circulation and change after delivery. They are as follows:

• The umbilical vein transports blood rich in oxygen and nutrients from the umbilical cord to the underside of the liver. It has a branch that connects to the portal vein and provides blood to the liver.
• The ductus venosus connects the umbilical vein to the inferior vena cava (from a vein to a vein). The blood now combines with the deoxygenated blood returning from the lower sections of the body. As a result, the blood throughout the body is only half oxygenated.
• The foramen ovale (oval opening) is a brief aperture between the atria that permits most of the blood flowing from the inferior vena cava to transfer into the left atrium. Because the blood has already been oxygenated, there is no need for it to flow through the lung.
• The ductus arteriosus (an artery to an artery) connects the pulmonary artery bifurcation to the descending aorta, entering it immediately beyond the point where the subclavian and carotid arteries leave.
• When the hypogastric arteries penetrate the umbilical cord, they branch off from the internal iliac arteries and become the umbilical arteries. They transport blood back to the placenta.

The umbilical vein enters the fetus at the umbilicus and runs along the free border of the liver, transporting oxygenated blood (80% saturation) from the placenta. It gives off branches to the liver's left lobe and receives deoxygenated blood from the portal vein. The majority of the oxygenated blood combines with portal venous blood and inferior vena cava before entering the right atrium of the heart.

The valves of the inferior vena cava and crista dividends convey the majority of the blood (75 percent) in the right atrium towards the foramen ovale, where it enters the left atrium. It is combined with a little amount of venous blood returning from the lungs via the pulmonary vein at this point. The left atrial blood flows to the left ventricles via the mitral opening.

After passing via the superior and inferior vena cava, the remaining blood (25 percent) enters the right ventricle via the tricuspid aperture.

During ventricular contraction, left ventricular blood is pushed into the ascending arch of the aorta and distributed to the heart, head, neck, brain, and arms via their branches. The right ventricular blood, which has a low oxygen content, is discharged into the pulmonary trunk, with the majority of the blood passing directly through the ductus arterioles into the descending aorta bypassing the lungs and mixing with blood from the proximal Aorta, and only a small portion going to the lungs for oxygen and nutrient supply for both lungs. The descending aorta's mixed blood is disseminated throughout the body, and the majority of impure blood exits the body via the two umbilical arteries to reach the placenta.

References

• Embryology. 27 01 2017. 07 03 2017 < http://www.embryology.ch/anglais/pcardio/umstellung01.html
• Berkeley. http://mcb.berkeley.edu/courses/mcb135e/fetal.
• Tuitui R. 2002, A textbook of Midwifery A (Antenatal), 3rd edition, Vidyarthi Pustak Bhandari (Publisher and Distributor), Bhotahity, Kathmandu
• Wong, D.L., 1995, Whaley and Wongs, Nursing care of infants and Children, 5th edition, Mosby, St.louis, London, Philadelphia
• Saxton, D.F., 2001, Mosby’s comprehensive review of the nursing 17th edition, Mosby Yearbook, St. Louis-London, Philadelphia, Sydney.