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学习体循环肺循环的区别.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 what you're looking at is basically a kind of a mechanistic way of thinking about the heart almost as if it's a couple of pumps with pipes attached to the pumps and in a way that's that's not a bad way to think about the heart in fact we're gonna kind of move through this diagram and I realize it looks it looks a little bit scary but once I start labeling stuff you'll start seeing that it's actually not as bad as it seems so let's get started in the upper part of the heart the right atrium is right there and then blood goes down into the right ventricle and then on the other side I'm gonna label the last two chambers the left atrium and the left ventricle and we're gonna actually follow the path of blood after it leaves the right ventricle we're gonna start our journey here at the right ventricle so what's the first thing it kind of comes across well blood leaves the right ventricle goes through a valve and after on the other side you've got this area right here and I've drawn it as one tube with no split and this is the pulmonary trunk pulmonary trunk so blood is headed towards the lungs going first through the trunk and of course after the trunk there's a left and right so I'll write that up here the pulmonary arteries are next and remember I call them arteries because they're going away from the heart and there are two arteries so pulmonary arteries left and right pulmonary arteries and that's why you see two things here one here and you see one here and those those are basically tubes so it's going from the pulmonary trunk it's splitting into one of the two tubes and now I'm drawing the left and right lung up top and of course you know that the lungs are actually not gonna look this way so this is not anatomically correct but this is not as I said in the beginning a bad way of thinking about it so blood goes through the lungs and then comes out on the other side and there we're gonna talk about left and right pulmonary veins and actually here I'm gonna make the point that there aren't just two pulmonary veins one for each lung actually there are usually more than that and so when I draw this - I really want you to just think of the two sides veins coming from both sides the actual number could be a few it could be a few pulmonary veins in total the pulmonary veins drain blood then into the left atrium right so now we're on the other side of the of the heart and for the moment I'm going to kind of pause the journey here so we've gone from the right ventricle around to the lungs back again in the left atrium and this is kind of the first part of our journey and this part of the journey is called the pulmonary circulation I'm actually just going to write that here pulmonary circulation so the the fact that this part is going starting from the heart and going back to the heart is one circuit and our heart actually has two circuits but I want to point out this circuits one at a time and we've already kind of completed one circuit so I'm gonna just take some blue paint to indicate deoxygenated blood or blood without oxygen I'm gonna paint in how it would look and actually it stopped there because my arrows but you can actually see now the deoxygenated blood kind of goes from the right ventricle through the pulmonary trunk through the arteries and into the left and right lung and once it's there it's gonna kind of mix in with the capillaries and it's gonna start getting oxygen and then it's gonna come out on the other side in the pulmonary veins and it's again stopped a little bit there but I can fill it in and the pulmonary veins are gonna deliver that oxygenated blood to the left atrium so what you see kind of colored in now is the pulmonary circulation that's the first part of our circuit but let's now keep going and now talk about the second part of the circulatory system which is the systemic circulation so now the journey starts with the left ventricle so let me start there so for the systemic circulation I'm going to start the left ventricle and it's gonna go around to the body right the body is kind of the thing that's gonna be receiving all of the blood and when I say body I really mean lots of things I mean things like the brain so it could be an organ like the brain or the liver it could also be you know maybe things like bones if you have bones and your fingers it could be the the toes it could be any part of your body that you can think of right so all these different organs and tissues are gonna be getting blood from the left ventricle it's gonna be going initially through a giant vessel this vessel I'm gonna label let's say here as the aorta so this large vessel is the aorta and of course it branches and splits and I haven't shown all the branches that come off the aorta but there are many many of them it goes to the various tissues and organs and then it comes back out on the other side and at the end kind of somewhere up here it's gonna go back to the right atrium and it generally travels through two major kind of vessels one is the inferior and the other is the superior meaning lower and upper and they're both called vena cavas so superior vena cava and inferior vena cava I'll just write that here so these are the two major veins that are bringing back blood from all the different parts of the body and so now you've actually seen the second circulation because it all ends at the right atrium and this is the systemic circulation I'm going to write systemic circulation here so now you can see that the heart is really two different systems or let's say two different circuits rather and the first one the pulmonary circulation is really kind of relying on the right ventricle as the pump and the second one is relying on the left ventricle as the pump and actually I can now that you've seen I can now color it in there it would kind of deliver all the blood to the various organs and then the organs would use up the oxygen so let me show it kind of now going back to blue just to indicate deoxygenated blood and it goes back to the right atrium as deoxygenated blood so this is kind of how we sometimes see it and again this doesn't show you or give you an appreciation for the anatomy exactly you know where things branch off often and where the different names make sense but you get a kind of overall feel for the fact that we have two different circulations and you can see where the blood is going for the two different circuits now when you look at this picture you could say well okay I guess you can see where all the different tissues are getting the blood basically sounds like everything is coming from the - blood coming out of left ventricle but some tissues always kind of trip people up or it's kind of spark a question and I'm just going to kind of try to target a couple of the tissues that I think people sometimes might have questions about and one of them wouldn't really call it a tissue but you could definitely call it a cell type it's the RBC and RBC just stands for red blood cell so people sometimes wondering you know if the red blood cells are carrying blood to other parts of the body then how did they themselves get oxygen you know do they just kind of use up some of the oxygen that they're carrying or or what exactly and to answer this question I would have to remind you that a red blood cell basically looks a little bit like this right in cross-section and it doesn't have any mitochondria no mitochondria so it has no mitochondria and remember mitochondria are these tiny little organelles inside of cells that are using oxygen so if it has no mitochondria then it is not really using auction so it's not using oxygen and really these cells we call them cells and they are in many senses of the word but they don't really have mitochondria they also don't have a nucleus I mean these are literally these amazingly designed cells that are made for the purpose of carrying around oxygen to the to the body because under that literally are bags of hemoglobin so just remember red blood cells don't really need oxygen they simply carry it around another tissue or organ that makes people kind of wonder is the heart the heart is pumping all the blood around but does it actually get oxygen from vessels that are in the pulmonary circulation or from the systemic circulation or what and here the short answer is systemic circulation that's kind of the quick answer and let me actually show you where the blood vessels come from these are called coronary vessels I'll just write the word coronary here coronary vessels so coronary artery and vein and these coronary vessels they they come right off the aorta here and here so they kind of come off of the aorta right away they're the first branches off the aorta actually so the first branches go and serve the heart so it's kind of the first to get systemic circulation blood and the veins actually drain in to a spot directly into the right atrium so there's actually a little spot right there that they drain into so the the blood from the arterial side is coming from the aorta and on the venous side it's actually not even dumping into the inferior or superior vena cava kind of a little known fact it's going directly into the right atrium and finally kind of a tricky one but the lungs where do the lungs get their oxygen from and this is I say tricky and I kind of saved this for last because there are actually blood vessels and again don't worry so much about the anatomy in terms of like where is it coming off of exactly but it's coming off of the systemic circulation and you've got a vessel going to the right lung let's say something like that and you've got another vessel going I'll just draw it kind of going to the left lung like that so you've got a couple of arteries that are branching off and these are also part of the systemic circulation systemic circulation and these are called the bronchial arteries and these bronchial arteries bring then really a wonderful oxygenated blood right these are the bronchial arteries and you might say well that wasn't so so difficult I'll say bronchial vessels because they're also some veins coming off actually let me draw the veins now for you so you can see how those kinds of end up and these veins they come from of course the right lung and they actually end up kind of dumping in here you can't really show blue on blue but you know just trust they kind of go there and you've got another vein from the other lung kind of following a parallel path and going into the veins as well and so they don't dump necessarily directly into the inferior superior vena cava but I just want to show that they go into the venous side on the systemic circulation so if that was it that would be really simple but actually lungs are kind of interesting in the sense that there is a lot of mixing going on so you've pulmonary artery's carrying blood you've got bronchial arteries carrying blood and that blood mixes and then you've got at the capillaries you've got some some blood kind of from both places the the pulmonary circulation and blood from the systemic circulation again mixing and then on the on the other side where the you know veins are bringing blood back to the heart most of the blood as it turns out most of the blood actually goes this way into the pulmonary veins so even though you have you know bronchial arteries bringing blood in that would be right here you may have bronchial arteries bringing blood in a lot of that blood ends up going into the pulmonary circulation so that's kind of an interesting fact but not as much goes this way directly into that systemic circulation so it's kind of a tricky thing to keep in mind but the lungs then technically really are getting blood both from the systemic circulation but also they're kind of mixing blood and they're mixing blood with the pulmonary circulation we'll talk a little bit more about this in another video I don't want you to you know feel like this kind of got too confusing but but I just want you to be aware that there is mixing going on in the lungs with the systemic and pulmonary circulation they're kind of a neat organ in that sense