Physiology of the Non complicate Fetal Circulation
The normal growth and development of the fetus rely on an active, independent metabolism, but they also require an efficient circulation. consequently, we will be dealing with its mechanism and efficiency.
During fetal life, the lungs are essentially nonfunctional; consequently, less blood is needed for these organs than is required after birth. The fetal brain requires the highest oxygen concentration and the heart must pump a large amount of blood by the placenta. The characteristics of fetal circulation assure that the most vital materials for growth.
Blood carrying oxygen and nutritive materials from the placenta enters the fetal system by the umbilicus via the large umbilical vein. The blood then travels upwards to the underside of the liver where it separates- part of the blood enters the portal and hepatic circulation of the liver and the remainder travels directly to the inferior vena cava by way of the ductus venosus. Due to the higher pressure of blood entering the right atrium from the inferior vena cava, it is directed posteriorly in a straight pathway across the right atrium and by the foramen ovale to the left atrium. In this way the better oxygenated blood enters the left atrium and ventricle to be pumped by the aorta to the head and upper extremities.
Blood from the head and upper extremities entering the right atrium from the superior vena cava is directed downward by the tricuspid valve into the right ventricle. From here it is pumped by the pulmonary artery, where the major problem is shunted to the descending aorta via the ductus arteriosus. Only a small amount flows to and from the nonfunctioning fetal lungs. Blood is returned to the placenta from the descending aorta by the two umbilical arteries.
Before birth, the high pulmonary vascular resistance produced by the collapse fetal lungs causes greater pressures in the right side of the heart and the pulmonary arteries. At the same time the free-flowing placental circulation and the ductus arteriosus produce a low systemic vascular resistance in the remainder of the fetal vascular system. With the clamping of the umbilical cord and the expansion of the lungs at birth, the hemo-dynamics of the fetal vascular system undergo distinct and sudden changes. These changes are the direct consequence of cessation of the placental blood flow and the beginning of lung respiration.
consequently, we can conclude that the fetal circulation is not as complicate as that of the Adult or child since it gets its nutrient from the great number mother by the placenta. That is why for stimulation of activity of the lungs, the child would be tenderly hit after birth so as to make it cry for air to go into the lungs to begin its work.