Two circulations in the body Learn the difference between the pulmonary and systemic circulatory systems in the body. Rishi is a pediatric infectious disease physician and works at Khan Academy.
Two circulations in the body
- So what do you looking at is basically a kind of a mechanistic way of thinking about the heart.
- Almost it´s a couple of pumps with pipes attached to the pumps.
- And in the way, it´s not a bad way to think about the heart.
- In fact we gonna move through this diagram.
- I realize that it looks little bit scary, but once I start labeling these stuff you start to seen that it is actually not that bad as it seem.
- So let´s get started in upper part of the heart.
- The Right atrium. Right there.
- And the blood goes down into the right ventricle.
- And then on the other side I´m going to label the last two chambers. The left atrium and the left ventricle.
- We gonna actually follow the path of blood after leaves the right ventricle.
- We gonna start our journey here in the right ventricle.
- So what´s the first thing that kind of come across?
- Well, blood leaves the right ventricle, gones through the valve and after on the other side you´ve got, this area right here.
- And I 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 is left and right (write it up here) pulmonary arteries are next.
- And remember I called 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 are basically tubes.
- So it´s going from the pulmonary trunk, it´s splitting into one of the two tubes and I´m drawing these left and right lung up top.
- Of course you know that the lungs are actuall not gonna look this way, so this is not anatomically correct.
- But this is not as I said at the beginning bad way of thinking about it.
- So blood goes through the lungs and then comes on the other side and there we gonna talked about the 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 usually more than that.
- And so when I draw this to I really what you to just think of two sides, veins coming from both sides.
- That actual number could be a few pulmonary veins in total.
- The pulmonary veins drain blood that end into the left atrium right.
- So now we are on the other side of the heart.
- And from the moment I´m gonna kind of pause the journey here. So we´ve gone from the right ventricle around to the lungs back again into 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 gonna write it here - Pulmonary circulation.
- So the fact that this part is starting going from the heart and going back to the heart is one circuit.
- And our heart actually has two circuit.
- But I wanna point out these circuits one at the time.
- We´ve already kind of completed one circuit.
- So I´m gonna just take some blue paint to indicate the oxygen in blood or blood without oxygen,
- I´m gonna paint in how it look.
- And actually it stop there because my aeros, you can actually see now, the oxygen in the blood kind of goes from right ventricle, throught the pulmonary trunk, throught the arteries and into the left and right lung.
- And once it´s there it´s gonna kind of mixed in with the capillaries and it´s gonna start getting an oxygen.
- And then it´s gonna come out 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 delivered that oxygene of blood to the left atrium.
- So what you see is a kind of coloured in now is the pulmonary circulation.
- That´s the first part of our circuit.
- Let´s now keep going and talk about the second part of the circulatory system, which is the systemic circulation.
- So now the journey starts with the left ventricle. Let me start there.
- For the systemic circulation I´m going to start in the left ventricle and it´s gonna go round to the body.
- Right the body is kind of the thing is going to receiveing all of the blood.
- And when I said body I really mean lots of things.
- I mean things like the brain, liver or it also could be maybe things like bones and your fingers, could be the toes, could be any part of your body that you can think of.
- It´s all these different organs and tissues that are going getting blood from the left ventricle.
- It´s gonna be going initially through a giant vessel.
- This vessel I´m gonna label let say here, as the Aorta.
- This is large vessel, the Aorta. And of course it branges and splits and I´ve not show all of the branges that´s came of the Aorta.
- But there are many, many of them.
- It goes to the various tissues and organs and then it comes back up on the other side.
- And in the end kind of some up here it´s gonna go back to the right atrium.
- And it generally travels trough two major kind of vessels.
- One is the Inferior and the other is the Superior, meaning lower and upper, and they both called Vena Cava.
- So Superior Vena Cava and Inferior Vena Cava.
- So these are the two major veins that bring you back blood from the all the different parts of the body.
- And now you´ve actually seen the second circulation, because it all ends up in the right atrium.
- And this is the systemic circulation. I´m going to write it here.
- So now you can see thet the heart is really two different system, let´say two different circuit.
- And the first one, the pulmonary circulation, is really kind of relying on the right vetricle as the pump.
- And the second one is relying on the left ventricle as the pump.
- And actually I can now that you see it colored in.
- That would kind of delivered all the blood the the various organs, then the organs would use up the oxygene, so let me show it kind of now going back to blue.
- That´s indicate deoxidized blood and then goes back to the right atrium as deoxidized blood.
- So this is kind of how we sometimes see it and again does show you or give you an appreciation for the anatomy exactly,
- you know where the things brand show and when the different name makes sence,
- but you get it kind of overall feel for the fact that we have two different circulation
- and you can see where the blood is going from the different circuit.
- Now when you look at this picture you can say well I guess I can see all the different tissues we´re getting into blood,
- basically sounds like everything is coming from the oxygene of blood,
- coming up to the left ventricle.
- But some tissues always kind of trick people out, for it is kind of sparkle question.
- I´m just going kind of try a target couple of that tissues that I think people sometimes may have questions about.
- And one of them, woudn´t really called them tissues, but you can definitely call them cell type.
- It´s the RBC and RBC just stand for red blood cell.
- So people sometimes wondered you know if the red blood cell caring blood to the other parts of the body.
- Then how they themselves get oxygene?
- You know do they just kind of use up some of the oxygene they´re caring or what exactly?
- And answer to the question I need to remind you that the red blood cell basically looks little bit like this right, in cross section.
- And it doesn´t have any mitochondria, no mitochondria.
- So has no mitochondria and remember mitochondria are these tiny little organelles inside of cells that using oxygene.
- So that has no mitochondria that it´s not really using oxygene.
- So it´s not using oxygene and really these cells, we call them cells and there are many sences of this word,
- but they don´t really have mitochondria, they also don´t have nucellus.
- These are literarily amazingly design cells that they are made for the purpouse of caring around oxygene to the body because they really are bags of hemoglobin.
- So just remember red blood cell don´t really need oxygene they´re simply caring it around.
- Another tissue or organ makes people kind of wondered is the heart.
- The heart is pumping all the blood around but does it actually get oxygene from vessels that are in the pulmonary circulation or from the systemic circulation or what?
- And here the short answer is systemic circulation.
- It´s kind of the quick answer.
- And let me actually showed you where the blood vessels come from.
- These are called coronary vessels. So coronary artery and vein.
- And these coronary vessles they actually come right off the aorta here and here.
- So they come off the aorta right away, first branches off the aorta actually.
- So the first branches go and served the heart.
- So it´s kind of the first to get systemic circulation blood.
- And the veins actually drain in to the spot directly into the right atrium.
- There is actually little spot right there and that they drained into.
- So the blood from the atrium come into aorta
- and on the vena side and it´s actually not even dumping into the inferior or superior vena cava,
- kind of little unknow fact that is coming directly into the right atrium.
- And finally kind of tricky one but the lungs.
- Where the lungs get their oxygene from?
- And this is like I said tricky and I save this for last because there are actually blood vessels
- and again don´t worry so much about the anatomy in terms where it is coming off in the exactly,
- but it´s coming off the systemic circulation and you´ve got the vessel coming to the right lung.
- Let´s say something like that. And you´ve got another vessel going, I´ve just drawing kind of going to the left lung like that.
- So you´ve got couples of arteries branching of and these are also part of the systemic circulation.
- And these are called the bronchial arteries.
- And these bronchial arteries brain that really wonderful oxygened blood right. These are the brochial arteries.
- So you might say that wasn´t so difficult.
- I say bronchial vessels because there are some veins coming off.
- Actually let me drawn the veins so you can see how those are kind of end up
- and these veins come from of course the right lung and they´re actually end up kind of dumping in here.
- Can really show blue on blue but you know just they kind of go there.
- And you´ve got another vein from the another 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.
- I´ve just wanna showed that they´re going into the vena´s side on the systemic circulation.
- So if that was it that would be really simple, but actually lungs are kind of interesting in sence that there is a lot of mixing going on.
- You´ve got pulmonary arteries caring blood,
- you´ve got bronchial arteries caring blood
- and that blood mixes.
- And then you´ve got the capillaries,
- you´ve got some blood kind of from both places -
- the pulmonary circulation and the blood from the systemic circulation again mixing.
- And then on the other side where the veins bringing blood back to the heart
- most of the blood turns out, most of the blood actually goes this way into the pulmonary veins.
- So even if you have the bronchial arteries bringing blood in that would be right here
- you know the bronchial arteries bringing blood in a lot of that blood ends up going int that pulmonary circulation.
- So that´s kind of a intersting fact that not as much goes this way directly into that systemic circulation.
- So that´s kind of the tricky thing to keep in mind
- but the lungs then technically really are getting blood both from the systemic circulation
- but also they kind of mixing blood and they´re mixing blood with the pulmonary circulation.
- We´ll talk about this little bit more in another video
- and I don´t wanna make you feel like this kind of got too confusing
- but I´ve just wanted you to be aware that there is mixing going on in the lungs with the systemic and pulmonary circulation.
- That´s kind of a unique organ in that sence.
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