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Unformatted text preview: CIRCULATORY CHANGES AT BIRTH I. Review of Fetal Circulation  The development of the cardiovascular system - … Begins to develop toward the end of the third week … Heart starts to beat at the beginning of the fourth week … The critical period of heart development is from day 20 to day 50 after fertilization. … Many critical events occur during cardiac development, and any deviation from this normal pattern can cause congenital heart defects, if development of heart doesnít occur properly. … However, we will concern ourselves with the events surrounding the circulatory changes at birth. Trace path of blood in diagram of fetal circulation (see diagram) Three shunts in the fetal circulation  1. Ductus arteriosus … protects lungs against circulatory overload … allows the right ventricle to strengthen … hi pulmonary vascular resistance, low pulmonary blood flow … carries mostly med oxygen saturated blood 2. Ductus venosus … fetal blood vessel connecting the umbilical vein to the IVC … blood flow regulated via sphincter … carries mostly hi oxygenated blood 3. Foramen ovale … shunts highly oxygenated blood from right atrium to left atrium II. Review of respiratory changes and other changes at birth Overview … As soon as the baby is born, the foramen ovale, ductus arteriosus ductus venosus and umbilical vessels are no longer needed. … The sphincter in the ductus venosus constricts, so that all blood entering the liver passes through the hepatic sinusoids. … Occlusion of the placental circulation causes an immediate fall of blood pressure in the IVC and right atrium. Circulatory Adjustments at birth: Increasing uptake of oxygen by lungs (first and subsequent breaths) induces a vasoconstriction of ductus venosus and ductus arteriosis Aeration of the lungs at birth is associated with 1. a dramatic fall in pulmonary vascular resistance due to lung expansion....
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This note was uploaded on 05/04/2008 for the course NURS 230 taught by Professor Knobloch during the Spring '08 term at Lady of the Lake.

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