So the job of our lungs on a pretty general level is to take blood, that’s without oxygen that our bodies have used up. So I’m going to use bluehere to represent that. To take that blood andto put oxygen in it, and it comes out as oxygenated, which is red blood. I mean blood without oxygengets a little darker, that’s why conventionally we think of it as blue versus red. And from there the heart pumps this blood to the rest of the body. So in a nutshell, that’swhat the lungs do. And to do that, they grab oxygen from the atmosphere and take the carbon dioxide from the blood and blow it out. Co2, carbon dioxide.
And this exchange really is a full picture of what you do with every breath. Now in terms of how the lungs do this, let’s talk about thestructure first for a bit. I think it looks kind oflike an upside down tree, just because all thesebranches keep getting smaller and smaller as we reached the terminal branches. I mean there’s 20 or 30 levels here, I can’t draw them all, but you get the idea,they keep branching off. And at the end, we’ve reached this units called alveoli. Let me write that word for you, alveoli. Which is plural for alveolus. And what that is essentially an air sac. Let’s blow that up down here. So the alveolus looks kind of like a bulb, is an air sac, it has very thin walls, and laying along the walls, almost, almost in contact but not quite, is the blood supply. This is how things get from our blood to the lungs and back and forth. So I’m going to draw ablue here to begin with because there’s no oxygen to begin with. As it travels and that theair goes back and forth between the blood supply and the alveolus, it becomes red as it leaves, because there’s oxygen. You can think of it as inhale, oxygen goes in, from here it goes to the blood supply. It makes you exhale, the carbon dioxide isgoing the opposite way. When we exhale it canjust leave the lungs. And now the reason thisexchange takes place is just a simple loss ofair pressure in physics. So if there’s more oxygen in here, relatively more compareto the blood supply, then the oxygen wants toescape to the blood supply. And if there’s relatively more carbon dioxide in the blood, then it also wants to escape to where there’s less of it, which is into the air sac. So conveniently this allowsus to take what we want and get rid of or it don’t want anymore. Okay, so there’s your bird eye view of how the lungs work in a nutshell. And there’s a lot ofproblems that can arise in this whole system. But I think a better way to understand it is to break it down bythe different players, the different areas that can go wrong. So again we think of lungproblems as categories. Now, the first one, the first problem I can think of is oxygen not coming in. And so on the flip side of that, number two would be carbondioxide not escaping. All right to keep going, let’sgo further into the lungs. Here at the alveolus, I would say number three is something going onwith this exchange process where between the airsac and the blood supply, something is not working there, so that’s number three,that’s the exchange. And lastly, if something iswrong with the blood supply, blood cannot get tothe lungs and come out, that would be number four. So I think these are the four big categories of lung diseases. And let’s go through them one by one. Now problems number one and two here, we actually think of themas a pair of diseases, there’s restrictive and obstructive. Let’s start with restrictive. And this just describesthe fact that the lungs which are suppose toexpand when you take air in to make room for the air, for some reason it’snot expanding properly. So this is an intakein respiration problem. And since oxygen is themain point of taking air in, in restrictive diseases we lack oxygen. So what happens is, the lungs for a variety of reasons becomes stiff and hardto blow up like a balloon that’s been dipped in paper mache and it can’t blow up properly. So if you look at, ifthis is suppose to be the size of the lung when it’s blown up, this smaller lung herin restrictive disease gives us a lot of wasted space, other space that could have had oxygen but is now not usable. That just makes the whole system less efficient, right? So there’s something wrong with the actual structure of the lungs that’smaking it hard to expand.
So let’s think of some examples. So there’s fibrosis. Fibrosis just means, laying down too much scar tissue. So if the lungs are chronically injured or sometimes there’s agenetic factor to it, the tissue gets stiff. Just like the scar youwould have on your hand, except you have all over your lungs. So it’s not, no longer expandable. There’s also things thatcan affect the chest wall. Say if there’s a musculardiseases that make it hard for the chest to expand, that also limits howbig the lungs can get. Or sometimes therecould be things that are deposited in the actualtissue of the lungs, I can think of amyloidosis, which is these protein particles that get studded into the lungs, making it harder to expand. So those are our examplesof restrictive disease, oxygen cannot get in. Now it’s evil twin, or Iguess they are both evil, but it’s counterpart wouldbe obstructive disease. Obstructive. So if we said before that, the restrictive is aboutnot getting air in, then the opposite willnot be getting air out. In restrictive diseases we’re having trouble with expiration. So instead of letting thelungs collapse back to it’s normal size at the end of an exhale. It stays expanded like this. Let me just draw some of the branches here just to show you. There’s different reasons that obstructive diseases can occur. Sometimes, let’s saythere’s a mucous plug. An air can’t get out or sometimes these airways collapse because the walls have loss it’s elastic quality structure. So the air is essentially stuck in there. Let’s think of all these extra air. Can you imagine how difficult it would be if you cannot exhale, that’s very uncomfortable. So obstructive disease describes large, over-inflated lungs. And some examples would be something you probably heard of as COPD, which is actually a groupof two different diseases.
One is emphysema, which have to do with the lungs losing their elastic quality, and the other one is chronic bronchitis, which is just a lot ofirritation day in and day out, that makes a lot of mucous. Both of these result inthis large inflated lungs. Something more common that a lot of people have is asthma, which is when the air waysspasm and they close up, blocking the air from getting out. So restrictive and obstructive diseases going have to do with aglobal picture of the lung. Not to get into too much of the detail, just think of restrictiveas having trouble getting air in, oxygen in, and obstructive, having trouble getting carbon dioxide out with the exhale. So now let’s zoom back in to the alveoli. What’s going on down here that could give us lung disease.
So number three I said there’s something wrong with exchange. So let me just redraw this here. We have our air sac, so air has finally made it here to where it can make contact with the blood supply. And one thing that willreally mess up this process is let’s say if this airsac is filled with fluid. Like that. Let’s fill that in to make it, yeah, like that. Okay, so what would happen to your oxygen, so it’s coming in here, it wants to get to the blood and uh-oh, it’s stuck. As you know it’s muchharder for air to diffuse through liquid than itis when it’s empty space. And then on the other hand, carbon dioxide is here trying to get out and uh-oh it’s stuck in the fluid too. So as you this makes the whole exchange much less efficient. So you have less oxygen going in and less carbon dioxide going out. So that when, I would say that this blue, let’s extend this a little further, instead of turning redwhere it’s suppose to, since it’s so inefficient, it eventually becomes as kind of weak red when it leaves. So you have less oxygen in your blood and more to carbon dioxide than you would in a healthy lung. So what could cause thisto happen with the fluid. One thing that’s very common is an infection such as pneumonia. See when our lungs are not doing well, there’s a lot of secretions, mucous, which is fluid trying to flush out, wash out what’s there. So pneumonia, if it’s bacteria or virus this fluid happens. There’s also edema. Edema kind of is just a general word for a fluid being where it’s not suppose to, being pushed out. So, if for some reasonif there’s too much blood in the blood supply. Let’s say if your heartis not working well, and all this blood is backed up, then it will flow into the air sac where it does not belong and give us this pictureof wet inefficient lung. And usually the lungs worksbest when they are dry, because we’re talkingabout air exchange here. I forgot to write aname for this category, let’s call this ventilation. We’re talking about the exchange here, but ventilation technically means getting carbon dioxide out of here. But I want to use thisword to just describe the process of exchangingone gas for the other. Which is not working well here. And talking about wetversus dry lungs here, it kind of goes nicelyinto our fourth point. So our fourth problem, let’s call it a problem with perfusion. So it’s funny, it’s kind oflike the lungs are too dry. So perfusion is the ability to get blood where it’s suppose to go. Again let’s draw our alveolus, singular, it’s alveolus. So we have our bloodsupply coming in as usual and uh-oh, sometimes there can be a clot. So our body can make clotand they can break off and float in the bloodstream when they get to a place that’s smallenough to get stuck, they get stuck here. And stops the blood fromflowing pass this point. So for the rest of thepath, there’s no blood. And the branches of blood supply, the branches of pastthis point are also gone. So as you can see in this scenario, no matter how much oxygen we have in here, we only have, we don’t have any bloodsupply to put it into. So not having enoughperfusion is a huge problem, and we call it a pulmonary embolus. So pulmonary means it’s in the lungs. Embolus describes a clot that formed somewhere else and it’s travelled. And if it gets lodged in the lungs and it’s a pulmonary embolus, now the severity of thisreally has to do with where in the blood supply get stuck.
So let me just go back here, up here and draw some blood vessels along these trees. So if this embolus is all the way up here in a major branch and it shuts off this whole part of the lung. They have a huge problem,people can die from this. Now if it’s a very small branch, like down here, then it’s still uncomfortableand you’ll lose a portion of the lungs but it’s not relatively not as a big of a problem. But of course it will still compromise how well your lungs are working, how much oxygen is getting in, so on and so forth. So here you have fourvery general categories of lung disease that I think provides a nice structure for, okay, what are thedifferent players involved, and what can go wrongto give us lung disease?