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进一步了解心脏,它的特征,以及心脏的三层结构。里希(Dr. Rishi Desai)是一名儿科传染病医师,是可汗学院团队一员。 Rishi Desai 创建




so you're probably feeling pretty comfortable with the diagram of the heart but let me just go ahead and label a few things just to make sure we're all on the same page so blood flows from the right atrium to the right ventricle and then goes to the lungs and then the left atrium to the left ventricle so that's usually the the flow of blood and one of the things that keeps the blood flowing in the right direction we know is the the valves and two of the valves I'm actually going to name that give you a new name something slightly different from what we have been referring to them by these are the atrioventricular valves and you can take a guess as to which ones I'm referring to atrioventricular valves are the two valves between the atria and the ventricles so one will be the tricuspid valve and the other is the mitral valve and just to orient us this is the tricuspid the T and this is our mitral RM and the atrioventricular valves these two valves if you look at them they're both kind of facing downwards and one of the things that you might be wondering is well how how is it that they aren't just flopping back and forth and these valves in particular have a very interesting strategy and that is that they actually are tethered they're tethered to the walls so they're held down here like that and they have on the other end of those tethers a little muscle a little muscle there now this makes perfect sense if you think about it because the ventricles are very strong right we know the ventricles are really really strong and so if the ventricles are squeezing there is a good chance that that Bloods gonna shoot up in any direction it can go right it's gonna go back perhaps through the mitral valve if it can go there it will go through that tight Hospital if they can go there but the the reason that it won't is that these papillary muscles are basically kind of sending out little life lines these chordae tendineae life lines to keep the valve from flipping backwards so these chordae tendineae these cords are important for that reason right they're keeping the the valve from flipping backwards so these are all chordae tendineae and these are all the papillary muscles and these are particularly important than we can tell for when you're trying to make sure that the ventricles don't screw up the valves and now let's say that by accident let's say our ventricle is just too strong too powerful let's say that it broke one of these cords let's say it broke this one right here and that's because our ventricle is just forcing too much blood back and it just snapped the cord what would happen well this would basically kind of start flipping back and forth they would flip this way and this way and then on the next heartbeat blood would start going the wrong direction right because this valve is not able to keep that nice tight seal and so blood would basically kind of go this way when it wasn't supposed to and all of a sudden our flow of blood is now going in the wrong direction so the chordae tendineae and the papillary muscles do a really really important job in preventing that from happening so now let's let's move our attention to another area let's focus on this right here which is the inter eighth inch or sorry ventricular ventricular septum and you can think of septum is basically a wall intraventricular septum in this intraventricular septum the one thing I want to point out which is may be fairly obvious when you look at you might think well why did you even have to say it that's pretty obvious this area is really thin and this area is really thick by comparison right so the two areas are not equal in size this is much thicker and the reason I wanted to bring that up is because this first area in blue is called the membranous part literally like a membrane membranous and the bottom the red part is the muscular part this is the strong muscular part so you have two different areas in that intraventricular septum the wall between the ventricles and one of the interesting things about the membranous part in particular is that a lot of babies are born with holes in that membranous part so when I say a lot I don't mean the majority of babies by any means but but one of the most common defects if there is going to be a defect would be that you would actually have a communication between these two so that blood can actually again flow from a place that it's not supposed to go and the left ventricle into a place it shouldn't be going the right ventricle so blood can actually flow through those holes and that is a problem so that is called a VSD and actually you might hear that term at some points I just want to point out where that happens VSD and while I'm writing VSD you can take a stab at guessing what it might stand for ventricular and s is septal septal against a pill just means wall and D is defect so a VSD is common most common in that membranous part more so than that muscular department now let's move on again to one final thing I want to point out which is I want to zoom in on the wall so here in a gray box I'm gonna kind of highlight what's going on in this wall and how many layers there are in this wall let me draw out a little rectangle to correspond to that little rectangle I drew on the heart itself so there are three layers three layers to the heart muscle and actually I'm going to go through all three layers and we'll start from the inside and work our way out so on the inside you have what's called the endocardium endocardium and i'm actually gonna draw the endocardium kind of all the way around here goes all the way around the valve so now you already learned that the valves now have endocardium it goes around the ventricle and as I showed you in the beginning also around the atrium and it goes all the way up and covers both the right and left side the endocardium is very very similar in many ways to the inner lining of the blood vessels actually so it's a really thin layer it's not a very thick layer and it's definitely it's the layer that all the red blood cells are kind of bumping up against so when the red blood cells are entering the chambers of the heart the part that they're gonna see is going to be the endocardium so this is what it looks like and this is that green layer all the way around that I've drawn now so if I was to draw it kind of in a blown-up version it might look like this right and it's a few cell layers thick and like I said on the inside you have some red blood cells bumping along so maybe this is one red blood cell and this is maybe another one and they would bump into that endocardium now if you go a little bit deeper to the endocardium what do you get to next well next you get to myocardium myocardium and that would be let's say the chunk the biggest chunk of our wall and that would look something like this and that myocardium you can kind of appreciate just without even having me pointed out because it's the most common part of this entire thing right so this is our myocardium myocardium and let me go back and actually label the endocardium as well the endocardium and on the other side and accordion and actually just notice that the the words are all pretty similar Myo means muscle and actually while I'm on my own cotton let me just point out one more thing the myocardium is where all of the contractile muscle is going to be right so that's where a lot of the work is being done and that's also where a lot of the energy is being used up so when the heart needs oxygen it's usually the myocardium because that's the part that's doing all of the work okay now on the other side of the motor cardema what do we have on the outside well we have a layer called the pericardium and let me try to draw that in for you pericardium is something like this kind of a thin layer and the interesting thing about pericardium is that there's actually two layers to it so there's actually something like this or you have two layers an inner layer and an outer layer and between the two layers you have literally a gap there's a gap right there and in that gap you might have a little bit of fluid but it but it's not actually cells I guess that's the biggest point it's not actually cells it's more just a little bit of fluid that hangs out there so this whole thing is called the pericardium pericardium now you may be wondering how in the world do you get a layer that has a gap within it so let me actually try to show you what happens in a fetus so let's say you have a little fetus heart tiny little heart like this and it gets a little bit bigger like this and then it finally gets into an adult heart something like that so this would be the adult heart right well at the same time that the heart is growing you actually also have a sac almost like a little balloon right and this balloon balloon actually begins to envelope the heart so this growing heart kind of grows right into the balloon and so this balloon kind of starts going around it like that and you get something like this and then eventually as the heart gets really big you get something like this you basically have this kind of inner layer of the balloon that's pancaked out it doesn't even look like a balloon anymore it's very flat and then it kind of folds back on itself like that and it comes all the way around and now you can see why even though it's continuous I mean it's not like it breaks it is continuous here it's continuous there you can see how if you actually just were to look at one chunk of it like we like we're looking at right here you can see how it would actually look like a like a pancake and so on our heart actually it literally would be something like this like a very thin kind of pancake and I'm not doing a very very good job making it look thin but you can imagine what it is that it could look like if I was to zoom in on it basically something like that where you have two layers that are basically just kind of turned in on themselves and both layers put together or called your pericardium now there are actually separate names for the two layers so for example the layer that's kind of hugging up against the heart this layer that I'm drawing right now this layer is called the visceral pericardium's so you call it the visceral pericardium and the name visceral this right here would be visceral and the reason it's called visceral is because viscera refers to organs so that's called the visceral pericardium and then this outer layer the one I'm drawing now is called the parietal pericardium parietal and that's the layer that actually is on the outside so let me label that as well so that's this guy that would be the parietal pericardium so now you can actually see the layers of the heart the endocardium myocardium and pericardium and actually just to throw you a curveball because I'm pretty sure you can handle it this visceral pericardium another name for it just because you might see it sometime is the epicardium sometimes you might see this the name epicardium and don't get thrown off it's really just the visceral pericardium it's just the outermost layer of that heart before you get to the parietal layer