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.
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