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Current time:0:00Total duration:10:31

Video transcript

so here we are we have our two lungs in the heart I'm just going to quickly label stuff we've got a right and left lung and we've got our heart and I want to make sure I label all the four chambers of the heart I've taken away a lot of the vessels I just want to focus on a couple of things here mainly the the blue blood vessel coming off of the heart the one I've drawn in blue which I'm going to label here is the pulmonary artery remember again arteries go away from the lungs so this is our pulmonary artery even though it's got deoxygenated blood in it right little counterintuitive but I think you got it now so this is our pulmonary artery and it's going to the left and right lungs and if we assume that there's let's say five liters of blood kind of flowing through the heart per minute that means that five liters are going to go through this vessel and some of that is going to go to the right and some is going to go to the left and you know if I just let's say I told you that two and a half liters goes to the left lung per minute let's just assume that then you know that the other half of that five liters the rest of it two and a half liters must also go to the right because whatever goes into this tube but almost like a straw on one end has got to come out on the other end so you just basically add up what's exiting and it's got to equal what's entering right so here we have the idea of flow and we've talked about flow in other videos but basically just want to restate it it's a volume over a period of time in this case we're using liters over minutes but really any kind of volume over time you could describe as blood flow now let's say that a tragic event occurs and I end up having a surgery to my lung and let's say this lower lobe let's say this underneath this yellow line is my lower lobe and above it is my upper lobe let's say my lower lobe needs to be removed right pretty pretty drastic thing to have happen but let's say this is what happens what would what would change in terms of my my blood flow well the thing that is going to change is my resistance is going to change right before I had this surgery let's think about it before I had the surgery I had a certain amount of resistance in this blood vessel and also some resistance in this blood vessel and let's say it's about the same just to kind of make things easy let's say the resistance was about the same so again I had a surgery and before they were you know removed removed the lower lobe just to make sure we are clear on what the surgery was so remove the lower lobe and before the surgery so before the surgery all right before up here what was the resistance well the resistance I was facing was remember we have a branch here so we have to add up the total resistance you remember how to do this total resistance I'll call it our total equaled 1 divided by 1 over R because we said that's what the resistance is right there 1 over R plus 1 over R and that second one is because of this guy so we just kind of add it up and I would say okay well that's equal to 1 over 2 divided by R and I can flip the whole thing around and I get R divided by 2 or 1/2 R so this is my total resistance 1/2 R it's a little counterintuitive the fact that you actually have half of the resistance just because you have a fork right the fork in the road meaning this fork right here offers you a chance to kind of go one of two ways and as a result the resistance Falls in half so after my surgery what was my resistance wall and my surgery this all kind of went away this is now all gone right because my surgery removed the lower lobe so this is now gone so what is my new our total well if I had to calculate it again I would say ok our total in this case it's actually really easy because it's just whatever's left right in this case the total is going to be just R so really my resistance went from 1/2 R to R and so my resistance really by removing the lower lobe it doubled my resistance when much higher right so this is the first interesting point is that by having a half a lobe removed my resistance went way up so on this side my resistance after the surgery is much higher than it used to be now remember this flow five liters a minute now you still have that much blood coming in but now there's extra resistance on the left side so what's the blood going to do well it's going to say well why would I go that way when I can go this way so more of the Bloods going to kind of go this way because there's more resistance on the left side and so I can actually you know I don't know exactly what the amount of flow would be but I can kind of take a guess and I would say well my guess is that the flow will be lower so I'm actually just redo these numbers I'm going to give you new numbers and let's say the new flows I'll write them in green are going to be three liters a minute and two liters a minute so they slap to add up to five of course you know that's that's not changed but you have more blood going to the right lung so here let me introduce another word so we talked about flow but now let me talk about perfusion and sometimes people actually think they're the same thing they they sometimes will use them kind of synonymously but really perfusion is volume over time and so so far you're thinking well it is about the same right but actually it's all divided by amount of tissue amount of tissue and when I say ammount I could either be talking about a volume of tissue or a weight of tissue so amount of tissue and let's just to kind of make this a little bit more concrete I'm going to assume that I'm going to use 100 grams here and that's often used not always sometimes you'll see other units but I'm going to use 100 grams here so let's now think about this entire scenario with the new numbers two liters a minute and three liters a minute in terms of perfusion what would that mean well let's say I weigh out my two lungs and here I only have an upper lobe on my left side left so let's say that weighs half a kilogram half a kilogram and let's say on the right side I've got a one kilogram let's say this is one kilogram these are the weights of my two sides and to figure out perfusion then all you really are doing is taking the flow because remember this whole chunk this whole part right here is just flow and dividing it by the amount of tissue so I could figure out perfusion pretty easily I could say okay on the right side let's do right side first I've got three litres Amit I'm going to write that as three thousand milliliters just to make it a little easier to see three thousand milliliters per minute divided by I said one kilo which is the same as one thousand grams so what does that turn out to be if I'm going to use 100 grams as my denominator I could say well that's let's say zeros cancel so I've got three hundred three hundred milliliters per minute per 100 grams of lung tissue right and so this is for the right side and I could do the same thing for the left side I could say well what would it be if a left side it would be I've got two thousand two thousand milliliters right we said two liters and of course the two and three I was just kind of estimating but we'd have to actually measure to see what the actual flow is but here I've got five hundred grams and so that works out to four hundred four hundred milliliters per minutes per hundred grams so what I wanted to show you is an interesting thing which is that you can actually have on the one side you know if I said which side the right or the left after my surgery which side has more blood flow well then this side has more blood flow right the right side has more flow but if I said which one has more perfusion more perfusion well it turns out that actually that left upper lobe is actually getting more perfusion so just because one side has more flow doesn't necessarily mean that it has more perfusion often times that is the case because you can see how closely flow and perfusion are related but it just depends on on you know exactly what the weight is for the tissue kind of a classic example of this I'm going to write out over here but you might hear people talk about sometimes is if you say this side is high and this side is low let's do flow and perfusion they'll say well if you have flow and you're trying to talk about different organs one of the organs with the with the highest flow in the body would be your liver this is let's say your liver all right this is your liver and then with a little bit less blood flow would be your kidneys right this would be your kidneys let's say alright K for kidney or actually I guess I'll spell it out I have enough space and then something that has almost no flow relative to the other two would be bones and actually compared to this if you are to now talk about perfusion it would actually look slightly different so for perfusion using these same three organs if I was to kind of rank them based on which one gets the most perfusion or blood perfusion the kidney actually does the best so here you have to take a certain amount of tissue and it's got to be the same amount so I'm just imagining if I took a little chunk of kidney tissue and if I did the exact same thing it took a little chunk of liver tissue and this is kind of the way to think about it is that if you want to balance things out you've got to take the exact same amount of tissue in this case it would be a hundred grams let's say maybe these boxes are 100 grams of tissue it would be something like this and this would be the bone so the liver ends up not doing as well right it gets a little bit less perfusion in terms of 100 grams the kidney does a little bit better when it comes to perfusion and the bones the sad little bones they actually don't get much blood flow and even if you do it by a hundred grams of tissue they actually don't get much perfusion either so this is kind of another way to think about it and you might hear these examples so I wanted to give them to you here