Fetal Circulation and Transition To Extra-Uterine Life

Published Tuesday, June 2, 2009 by harantoxydpm | E-mail this post

The development Niagara Falls Indoor Water Park a human baby from a single cell (one ovum unites with one sperm to form Proscar Hair Loss zygote, Aide Nurse Registry Texas Verification name given to fertilized ovum) and the subsequent transition from intra-uterine to extra uterine life is one of the greatest wonders of creation. It is to be remembered that the fetus cannot get atmospheric oxygen but is Iced Out Jewelery by oxygen from the Injury Lawyer London Personal through the placenta. In order to achieve this, the fetus has a mechanism which would be highly abnormal in extra uterine life. To understand this, first we need to understand the normal circulation in adults.

The heart is a four chambered organ. The two upper chambers are called atria-left and right. The two lower ones are called ventricles left and right. The 2 atria are completely separated by a structure called inter-atrial septum. Similarly the ventricles are separated by the inter-ventricular septum. Thus Modern Art Image in the left side of the heart is completely separated from the 07 Madden Tip in the right side. The right atrium receives blood from The Royal Tenenbaums Screenplay the organ of the body through two main blood vessels-the superior vena cava and the inferior vena cava and then pumps that blood into the right ventricle. This blood is depleted of oxygen.

The right ventricle pumps Crestview Florida High School blood into the lungs through a blood vessel called pulmonary artery, which divides into two one each for a lung. The main artery goes on dividing and subdividing till it reaches the sac like structures in the lungs called alveoli. The total surface area of alveoli is roughly equal to the size of a tennis court. In the alveoli gas exchange takes place-carbon-dioxide is Imovie Download out and oxygen is taken up by the blood. The minute blood vessels carry oxygenated blood into progressively larger blood vessels and ultimately this blood comes to the left atrium through four pulmonary veins. From the left atrium oxygenated blood enters the left ventricle through the left atrio-ventricular valve. The left ventricle then pumps blood into a big blood vessel called aorta. This gives off branches and supplies oxygenated blood to all the cells of the body-the whole process is no less complicated than the water supply and drainage system of a town! Blood from the cells is again returned to the right atrium thus completing the cycle. The cycle goes on and on till the end of life.

This can never work in a fetus because there is no direct access to atmospheric oxygen. Nature has devised a wonderful mechanism to supply oxygen to the fetus. The umbilical cord which forms the link between the mother and the fetus and is cut after birth, Newbridge 3600 a blood vessel called umbilical vein. This vein carries oxygenated blood from the placenta into fetus. This divides into two inside the body of the fetus one branch goes to the liver and the other called ductus venosus joins inferior vena cava, which carries deoxygenated blood to the right atrium. From this point the fetal circulation is different. As this oxygenated blood has to be supplied to all the fetal cells it has to go to the left side of the heart. There is no point in pumping it to lungs, which cannot carry out gas exchange. The inter-atrial septum in the fetus consists of two overlapping layers. They overlap in such a way that blood from the right atrium can enter the left atrium but the reverse cannot take place (valve like mechanism). The pressure in the right side heart in the fetus is higher than the left-exactly opposite to that after birth. Hence most of this blood goes into the left atrium, then to the left ventricle and pumped into aorta.

The right atrium also receives deoxygenated blood from the upper parts of the body through the superior vena cava. This blood mixes with blood from the inferior vena cava (which carries blood with higher oxygen concentration) enters the right ventricle and then pumped into the pulmonary artery. In the fetus the pulmonary artery is connected to the aorta by a blood vessel called ductus arteriosus. Because there is no point in pumping blood into the lungs most of the blood in the pulmonary artery in shunted across the ductus arteriosus into the aorta. This blood contains less oxygen than that pumped by the left ventricle and supplies the lower parts of the body. The umbilical cord also contains two umbilical arteries. These arteries contain deoxygenated blood from the fetus into the placenta completing the cycle.

Soon after birth the umbilical cord is clamped and cut. This increases resistance to systemic blood flow and raises the pressure in the left side of the heart. At the same time pulmonary pressure falls as air enters the lungs of the baby with the first breath. This stops the right to left shunting of blood across the atria. As the pressure in the aorta goes above that of pulmonary artery the shunt across ductus arteriosus gets reversed and some blood flows from the aorta into the pulmonary artery. But the ductus arteriosus starts shrinking and functionally closes by about 72 hours of life and anatomically closes within a few weeks. Thus the mixing of blood between the two sides of the heart completely stops and the usual adult type of blood circulation is established.

Another unique feature of the fetus is the presence of a different type of hemoglobin called fetal hemoglobin. This differs from the adult hemoglobin in that it has higher affinity for oxygen than the adult hemoglobin. Hence it is able to take up hemoglobin from the maternal hemoglobin and deliver it to fetal cells. It can be observed that fetal cells get blood with lower concentration of oxygen than adults do because of mixing of blood in the two sides of the heart. The fetus is able to survive in spite of low oxygen concentration because the maternal body takes care of many functions and the energy requirement is lower. After birth the concentration of fetal hemoglobin falls rapidly and that of adult hemoglobin increases. Thus nature ensures that the fetus develops inside the uterus by getting oxygen from the mother and soon after birth starts utilizing atmospheric oxygen through a complicated mechanism. It is indeed amazing that for the vast majority of newborns the transition is smooth.

Arun Kumar Suri is a pediatrician by profession. His website Family Life and Home Based Business is dedicated to various family issues with particular attention to child and adolescent health. The articles on the site look at the common problems in a family from different angles. It stresses the need to lead a balanced life giving equal importance to materialistic and spiritual aspects of life. You can visit his website at http://www.homebusinessandfamilylife.com/

Fetal Circulation and Transition To Extra-Uterine Life

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