If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content
Current time:0:00Total duration:9:47

Video transcript

I wanted to spend just a tiny bit more time on the concept of shunting just because it's so important in what we're talking about shunting is used in a lot of ways the medicine and it just means pushing something from where it's supposed to be or used to be to a new place here we're talking about blood going from its natural place of flow to a different place and I want to introduce the anatomically correct heart and I want you to sit here and watch me draw it so I drew it in advance and here it is so our heart doesn't actually look like the cartoon this is how it actually looks and we'll just go through this really quickly and label everything so this is still the right side and this is still the left side the right side of the heart receives blood from the body that's used up low in oxygen so here we have the right atrium and blood goes into the right ventricle here this blue thing that I've drawn connected to the right ventricle do you see how the blood in the right ventricle goes this way this is our pulmonary artery now every vessel that receives blood going out of the heart is an artery so even though this is deoxygenated blue blood is still an artery because it's coming out of the heart then we have our left atrium going into the left ventricle here this big red structure this is our aorta actually let's just write out the whole thing a Horta so if I'm a drop of blood or if I'm the Magic School Bus this is how I would go through this whole system so coming in here or here so the veins dump blood into the right atrium I go through here into the right ventricle there's a valve here and let's not worry about what it's actually called for the moment just remember that it's there so I'm in the right ventricle and from here I get squeezed into the pulmonary artery again so valve here from the pulmonary artery I go to our wonderful lungs and draw the lungs like this like a tree it's the right and left branches of the lungs here we pick up oxygen now our blood has oxygen the lungs return the blood to the heart through to the left atrium oh I didn't draw those here so here we have pulmonary veins even though it's carrying red blood now since it's going back into the heart it's a vein so pulmonary veins return blood here and here into the left atrium so now I'm in the left atrium and I go into the left ventricle through this valve and this big left ventricle pumps me into the aorta and from the aorta I go all over the body slow branches and that's basically my path through the heart and the lungs so look at these little discreet chambers and paths the blood even though it's in all very close together follows this pattern and the deoxygenated blood is separated from the side that has oxygen so shunting here again we're talking about right to left shunting because we are worried about people turning blue cyanotic so this blue blood on this side is going this way for shunting to happen there are two things that need to happen one there needs to be a path and two there needs to be somehow this force or pressure behind it to make it want to go that way this is just like plumbing now that I know anything about plumbing but basically blood follows the path of least resistance just like water does so let's think about how we can create a path for that to mix in the first place so one obvious one look at these big chambers we can have a hole here lots of people are born with different holes in their heart and sometimes they heal up sometimes they don't depending on what exact disease or structural abnormality they have we can have a big hold there the next place we can have a hole is between the atrium I didn't draw the septum here so there it is and of course we can have a big hole there interesting everybody is born with the hole here but usually closes within the first few seconds first few breaths for sometimes there's a hole it's always going to be there and then for babies especially when they're in the uterus there is a vessel here called the ductus arteriosus okay let's write that up ductus arteriosus and basically they need this when they're in their mom's belly because we don't breathe in the belly and since we get blood from the placenta this is a conduit to help us get blood to the body now to do with fetal circulation so the ductus actually begins to slowly close as soon as we're born so adults don't have this in fact even toddlers don't have this but in the first few weeks of life this is a very real path for blood to still go back and forth it's really cool that we have medicine to keep it open or closed it faster depending on situation but just remember that it's there oops I accidentally erased part of my aorta here earlier that's not supposed to be there okay so now pressure so I'm just going to put over here pressure equals resistance resistance for our x slow that's just our little physics for the day all I want you to remember from this is that pressure and resistance are related so the left and right side of the heart actually have huge differences in pressure and that all depends on what they're pumping against so the left ventricle is pumping into the aorta into the body so it's pumping against the resistance of our whole bodies worth of vessels the left side the pressure actually equals our blood pressure so jumping out of the babies mentality for a while for adults what is our perfect blood pressure it's around 120 right that's the systolic pressure or the pressure the heart is pumping against when it's squeezing so the left ventricle when it squeezes it's pushing against 120 or so millimeters mercury I'm throwing numbers out there just do it so we have the comparison because on the right side the ventricle is pushing what into the lungs and the resistance in the pulmonary vasculature it's much much lower than our whole body so the right side is actually pushing against the range is usually 9 to 18 millimeters of mercury all this to show you that look at how much harder the left ventricle has to work compared to the right ventricle that's why in adults in functionally normal hearts the left ventricle is a lot bigger and stronger it's just a stronger muscle than the right ventricle so if both of them squeeze together and even if we have a hole here you would think that the normal shunt goes from left to right because this side has so much more power and you'll be right because we certainly have a lot of diseases would love to write shunts so we have right to left shunting about why is the right side overpowering one important one is because pulmonary vasculature in newborn babies have high high high resistance so initially the right side is pushing against a lot more pressure than the left side so in a newborn baby is very easy to go right to left because given the choice the blood rather go into the left ventricle then the pulmonary artery because the resistance in the lungs is so high and I say that again just because it's really important so if you're a drop of blood go back to let me use orange if you have the choice to go in here or in here in a newborn going to the pulmonary artery is hard because the lungs are stuffed and full of resistance while going to the left is a lot easier so it's going to go this way that's one important way of right to left shunting and that's why it's so prevalent in newborns in fact in adults this can still happen adults can develop pulmonary hypertension so the resistance can increase because of some disease in adults and we can still go right to left so that's one way to go right to left is the lung skipping us too much resistance the other way is look at this valve here this is called the pulmonary valve that connects the right ventricle to the pulmonary artery this valve can be too tight this artificially increases the resistance here so again blood the choice between here and here is going to want to go to the left side so that's also how you get shunting sometimes in some cases we don't even have a left ventricle it just didn't develop in that case the pulmonary arteries in aorta can be plugged over here that can be both receiving blood from the right ventricle I guess that's not really shunting as much as blood from the right side and left side just mixing together and going out so this is not an exhaustive list of all the ways we can shunt but the one thing I want to use this to illustrate is that when we talk about the specific defects in the heart always be thinking about the path that the blood wants to go and the pressure I guess and resistance that's making it go that way we got fluid and we got muscle and dust so no matter how it gets structurally messed up and then coming back to this picture will help us understand why this baby is blue or cyanotic