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Unformatted text preview: xygenated blood will go into the right atrium and you don’t want oxygenated blood going back into the lungs Changes in the umbilical vessels begin to establish. – slowly get fibrotic changes ­­ Right ventricle is thicker than left ventricle during fetal stage ­­ Right ventricle is thicker than left ventricle during fetal stage ­­ During neonatal stage the left ventricle progressively gets thicker than the right ventricle ­­ by the end of 1 st month. Factors influencing changes in circulation after birth: Fall in pulmonary vascular resistance because there is free flow from right ventricle into the lungs so the right ventricle need not work too hard because the resistance isn’t much Increased blood flow in pulmonary circulation because the lungs start to get thinned out and expanded starting from the first breath (Increase in the size of the lungs) Constriction of sphincter of ductus venosusConstriction Mechanical pressure differences the left and the right atria, and oxygen saturation in the aorta - mechanical pressure differences closes the foramen ovale and also the saturation of aortic blood is increased i.e. there is no more mixing of venous and arterial blood in the aorta because the venous blood is going into the lungs – this is a very important influence of closure of ductus arteriosus; closure of it depends on presence of normal oxygen tension – if oxygen tension is low for any reason in the aortic blood you can hav...
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