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Fetal Circulation

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All of the respiratory, excretory, and nutritional requirements of the fetus are supplied for by dissemination across the placenta as an alternative to the fetus’ organs including the lungs, kidneys, and gastrointestinal tract. Fetal circulatory systems are adaptive to these circumstances. The circulation of blood through a fetus is essentially diverse from blood circulation in an infant. Respiration, the procurement of nutrients, and the eradication of metabolic wastes transpire all the way through the maternal blood as a substitute of the organs of the fetus. The fetus is essentially helpless which means that many of the organs are incapable of independent function.


The capillary exchange flanked by the maternal and fetal circulation occurs and is contained by the placenta. This notable configuration, which includes maternal and fetal capillary beds, is discharge following deliverance as the afterbirth. The umbilical cord is the union between the placenta and the fetus, serving as the lifeline for inoperable organs. It consists of one umbilical vein and two umbilical arteries, enclosed by a gelatinous substance. Oxygenated and nutrient laden blood surges through the umbilical vein toward the liver. At this point, the umbilical vein segregates into two distinct segments.


Fetal Circulation
Image: Fetal Circulation

The first segment conjoins with the portal vein, and the secondsegment, called the ductus venosus finds its way into the inferior vena cava. Thus, oxygen laden blood is combined with the venous blood arriving from the lower extremities of the fetus before it gets to the heart. The umbilical vein is the only vessel within the fetus that transports completely oxygenated blood. The inferior vena cava dumps into the right atrium of the heart of the fetus. The vast majority of the blood traverses from the right atrium into the left atrium through the foramen ovale, which is the opening situated between the two atria. It then mixes with a diminutive amount of blood traversing back through pulmonary circulation. The blood then traverses into the left ventricle, where it is pumped into the aorta and throughout the fetus. A percentage of the blood entering the right atrium passes into the right ventricle and out of the heart by means of the pulmonary trunk. Because the lungs of the fetus are undeveloped and therefore are not functional, only a minute fraction of blood maintains through the pulmonary circulation. Blood flow resistance is exceptionally elevated in the collapsed lungs of the fetus.


The majority of the blood in the pulmonary trunk travels down via the ductus arteriosus which leads into the aortic arch. It then mixes with blood entering from the left ventricle. Blood is returned to the placenta by the two umbilical arteries that rise from the internal iliac arteries. In the fetus oxygenated blood is transfered by the inferior vena cava to the heart, and through the foramen ovale and ductus arteriosus to the systemic circulation.

Vital enhancements happen in the cardiovascular system once the fetus leaves the birth canal. The foramen ovale, ductus arteriosus, ductus venosus, and the umbilical vessels are not needed post partum. The foramen ovale immediately shuts down with the first breath of air because the relaxed amount of pressure in the right side of the heart forces a flap to obstruct the opening. This relaxation in the pressure occurs due to the vascular resistance to blood flow in the pulmonary circulation which then falls far below that of the systemic circulation as the lungs fill with inhaled oxygen. The pressure in the inferior vena cava and right atrium decreases due to the loss of the circulation within the placenta. The restriction of the ductus arteriosus happens slowly over a period of about 6 weeks post partum as the vascular muscle fibers compress in reply to the heightened level of oxygen saturation in the postnatal blood. The structure of the ductus arteriosus which then remains gradually atrophies and becomes a disassociated blood vessel.

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