Truncus arteriosus

truncus arteriosus requires us to go back a little bit into embryology or how this whole thing developed really quick let's label everything again right atrium blood goes into the right ventricle out through the pulmonary arteries just deoxygenated blue blood comes back into the left atrium as red oxygenated blood from the lungs left ventricle and it goes out this red tube the aorta into the body so that's how normal heart is in truncus arteriosus in the final step in developing this whole structure something went wrong so the pulmonary let me label this the pulmonary artery in the aorta they are like cousins they came from one structure and that was the truncus arteriosus during development is supposed to differentiate into these two different ones in a normal heart these two are completely separate to go their own way there's no mixing but in the truncus arteriosus that final step of differentiation never happened so instead of two distinct tubes like this it's still one so for that one big outlet that's connecting the two so it doesn't matter that the septum if it is intact if we have no ventricular septal defect even if the two ventricles are separate it doesn't matter because when blood goes into these two great vessels they mix anyway so even if we got some blue blood going in here and some red blood going in here as soon as they get in there they start mixing so we have purple blue and red mix purple right goes all the way in so since this is all one structure all of these septums don't exist anymore in fact I'm going to erase the name I just wrote because it doesn't really matter they're one structure in truncus arteriosus just erase okay in fact I'm going to open this up just to drive home the point that we are now operating with one structure okay but remember that these the ends of these great vessels are still plugged into what they're going so the structure is still going out to the lungs and then big overriding one is still going to the rest of our body so the lungs are receiving the same percent of oxygen in the blood as the body is as you can see that's why this baby is definitely cyanotic purple purple everywhere I think you get the point this is just fun to color in right now so truncus arteriosus is something that is pretty rare it's a genetic defect and like I said it happens in the womb but this is a very inefficient way of mixing all the blood together and we don't get very much oxygen into the body thankfully though we can artificially put in a septum just to separate the right side from the left the deoxygenated from the oxygenated from this you can see our normal anatomy of separating the oxygenated from the deoxygenated blood is really the most efficient way so with truncus arteriosus we just have to restore that by separating these two great vessels