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Changes in the newborn at birth
While the fetus is still in the womb, the lungs are full of amniotic fluid and are not used for breathing. Waste removal as well as oxygen exchange occur through the placenta. At birth, the baby's body must suddenly adjust to new processes for sustaining life in its new environment.
While the fetus is in the womb, blood flows through the placenta. There, waste products are removed and oxygen is picked up through an exchange process with the mother's blood vessels. This is done through membranes, and normally the fetal blood does not come in contact with maternal blood. The cleansed and oxygenated blood flows through the large umbilical vein through the liver and the ductus venosus to the inferior vena cava and finally into the heart. A small amount is pumped to the lungs, but a majority flows through the foramen ovale and the ductus arteriosus into the aorta where the blood is then distributed throughout the body. The deoxygenated blood is then returned through the umbilical arteries to the placenta, where waste products are removed and the blood is reoxygenated.
Once the cord is cut and the baby takes his first breath, a number of changes occur in the newborn's vascular system. The increased oxygen in the lungs causes a decrease in blood flow resistance to the lungs. There is also an increase in the blood flow resistance of the body's vessels. The lack of umbilical blood flow, decreased pulmonary vascular resistance, and increased systemic vascular resistance cause a closure of the foramen ovale. All the other vascular (blood supply) peculiarities of the fetus begin to constrict and eventually turn into supporting ligaments with no vascular responsibilities.
Update Date: 5/24/2002Elizabeth Hait, M.D., Department of Pediatrics, Rainbow Babies and Children's Hospital, Case Western Reserve University, Cleveland, OH. Review provided by VeriMed Healthcare Network.
Last updated: Tue, 06 Jan 2009 00:20:03 GMT