This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pediatrics
[{'content': 'Anatomical closure of ductus arteriosus occurs at – \nSelect and explain. \nA. Birth, B. 3–4 day, C. 10th day, D. 30th day', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Circulatory adjustments at birth \n\nThese are brought about because of a shift from placental dependance for gas exchange in the fetus to pulmonary gas exchange in the neonate.\n\n1) Pulmonary circulation\n\nImmediately after birth lungs expand due to the first few breaths of the neonate.\nThis causes a fall in pulmonary vascular resistance (O2 causes pulmonary vasodilatation).\nThis results in increased flow into pulmonary trunk and arteries.\nThe pulmonary artery pressure falls due to lowering of pulmonary vascular resistance.\nThe pressure relations between the aorta and pulmonary trunk are reversed so that the blood flow through the ductus arteriosus is reversed → Instead of blood flowing from the pulmonary artery to aorta, the direction of flow through ductus, is from the aorta to pulmonary trunk.\nIncreasing oxygen saturation causes the muscle of ductus to constrict →\n\nIn full term neonates, the ductus\xa0 arteriosus closes within 10 to 25 days.\n2) System circulation and circulation through the heart\n\nLoss of placental circulation and clamping of the cord after birth results in an increase in systemic vascular resistance.\nThis tends to increase the aortic blood pressure and the left ventricular systolic pressure.\nThe loss of placental circulation results in a sudden reduction of flow through ductus venosus which closes off\xa0 → Flow through ductus venosus disappears by the 7th day of postnatal life.\nThe loss of placental flow results in a decrease in the volume of blood returning to right atrium → Right atrial pressure decreases.\nThe left atrial pressure becomes higher than right atrial pressure and the septum primum which ats as a valve of fossa ovalis, approximates with the septum secundum to close off formen ovale.\nFunctional closure of foramen ovale occurs very quickly.\nOver a period of months, the septum primtun and septum secundum become firmly adherent resulting in anatomical closure of the foramen ovale.\nAfter closure of ductus arteriosus, there is establishment of postnatal circulation : -\nThe blood reaching the right atrium through IVC and SVC is emptied into the right ventricle from where it is pumped into pulmonary trunk.\nAfter coursing through lungs for gas exchange, it reaches the left atrium and ventricle.\nThe left ventricle pumps it out for distribution in the body for oxygenation of the tissues.\nThe venous return again comes back to right atrium through IVC and SVC.\nAll of the blood leaving the right ventricle, after coursing through lungs, reaches the left ventricle → The two ventricles are connected in series and therefore, the output of right and left ventricles are same (in contrast to fetal circulation, where right ventricular output is more).', 'role': 'assistant'}]