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Studying for a test? Prepare with these 14 lessons on Respiratory system diseases.
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Voiceover: Before we start to talk about lung cancer, I want to talk about the basics of the lungs. The lungs are made up of lots of airways that branch, and every time they branch, they get smaller and smaller and smaller and smaller and eventually they end in these sacs called alveoli. They end here because at the alveoli is where gas exchange occurs with the blood that I am drawing in red to represent the capillaries, where blood is flowing, but all these branch airways need to be protected from everything else that is in the body cavity, and so there is a lung lining that is made up of sheets of cells that form the boundaries of the lungs and keep everything well contained. Immediately around the lung lining is this protein-rich fluid, and this fluid is pretty important because when you take a breath in, your lungs expand and when you breathe out, they contract. So, there needs to be a way to accommodate this change in the size of your lungs and this fluid helps to do that, but we don't want fluid just seeping into the body cavity and so it also needs to be contained. That means that there is another lining on the other side of the fluid keeping it well contained. Let's go back to the airways for a minute because the airways are supported by lung tissue and if we take a section of them here, I will explain more what I mean. So, let's draw some cells here. These cells are very close together and they are actually kind of glued together. They have a special name called epithelial cells, and they set up the borders of the airway. So, here I'm drawing a little squiggly white line to represent air that is going to be flowing through this airway. On the other side of the epithelial cells is where the lung tissue is, so you can already see that these cells are anchored to the tissue and help to keep the structure of the airway. I'm going to go come back and talk about more of the proteins and the structures that you would find in the lung tissue, but for a minute, let's just focus back on these epithelial cells. Let's just imagine for a minute that one of these cells becomes damaged or mutated and starts to grow uncontrollably. That's really important because that's one of the things that defines cancer cells from other cells in your body. There's just no way to stop them from dividing. To accommodate more and more cells, these cancer cells start to push in on the airway and they also start to push in on the tissue underneath them taking away space from both of these areas. In the airway, this is a problem because air can't flow nicely through these airways anymore. Lung cancer patients are going to wheeze as a result of that and they are also going to feel a decrease in lung function. That decrease might not be so bad if the cancer is in a smaller airway, but if this is in one of the main airways of the lungs, this can really be significant. Now, the air that we breathe carries with it a lot of dust and bacteria, and when the bacteria gets deep into the lungs, it may be difficult for a lung cancer patient to remove the bacteria again past the cell mass, and so this sets up a perfect environment for the bacteria to settle down and cause a lung infection. So, the body's going to mount an immune response, and they're going to send white blood cells to the site of infection to try to kill the bacteria and clear the infection. So, here's my white blood cell. It's traveling through the blood, and the vasculature actually becomes leaky, allowing this white blood cell into the lung tissue to travel up to the bacteria so that they can actually kill the bacteria. During this process of the white blood cell migrating out of the blood vessel, fluid is going to follow it into the lung tissue. That's my yellow lines there, and the lung tissue is going to start to swell with this fluid. You can imagine that that means that all the lung tissue is going to be pushed out further into the airway. So, I'm going to draw that with dotted cells here to show you the movement of cells into the airway. That's going to increase all of the symptoms that the lung cancer patient is already experiencing with getting air in and out of these airways. Not only is the immune system responding to the lung infections, it is also responding to the lung cancer cells themselves because the immune system recognizes them as foreign. With all this activity, lung cancer patients will run an ongoing fever as a response from a chemical secreted by the immune cells as they respond. So, the immune system is really running a marathon here and requires a lot of energy, and unfortunately patients have trouble keeping up with these energy demands, and this contributes to unintentional weight loss. But let's go back to the lung cancer cells for a minute because these cells make a few things that are not typical of other lung cells, one of which is an enzyme that breaks down tissue around the cells, and this allows cancer cells to invade the lung tissue and surrounding structures nearby. If they migrate to vessels, like our blood vessel down here, they can gain access to them and travel throughout the body to other organs in a process called metastasis and form secondary cancers at these sites. Lung cancer cells can also migrate into the lung lining, like we had discussed in the beginning. Let's go back to our image here. They can migrate through the lining of the lung, where that protein-rich fluid cradling the lungs is located, and an immune response to cancer cells here is going to be a lot like what we just saw. It's going to cause swelling, and the swelling is going to take up space from the lung and make it even more difficult to breathe. So now that we now the reason for a lot of the signs and symptoms associated with lung cancer, you might be wondering what actually causes a cell to become cancerous in the first place. This is a really good question because I kind of just brushed over the fact that the cell becomes spontaneously mutated. In lung cancer, there are 3 main causes of mutations, one of which is smoking. In fact, smoking is so strongly tied to the development of lung cancer there is actually a unit of measure to determine how at risk a person is, depending on how often and how long they have smoked for. This unit of measure is a pack year, and that means... Let's say a patient has been smoking about 20 cigarettes a day. That is equivalent to a pack of cigarettes a day. You know what, let's say this person smokes three packs of cigarettes a day and they have been doing this for 10 years. So, this person would have been smoking three packs per day times 10 years for an equivalent of 30 pack years. 30 pack years is an important number because it places this person at a very elevated risk of developing lung cancer. Another mutation source is radon, and radon is a naturally-occurring gas that you find in the atmosphere that we are breathing in all the time. To explain where it comes from, I'm going to draw a tree rooted in some soil. There may be a house on top of this soil, and in this soil is a chemical that when it breaks down it releases this colorless, odorless gas called radon into the environment, and it can become trapped in houses and, particularly, in basements in houses. It builds up in high enough concentrations that this can cause lung cancer. Finally, a main last source of mutation in lung cancer is medical imaging, and if a person goes to the doctor and needs to have a picture taken of the inside of their chest, it might be taken with the use of radiation in the form of an x-ray or a computed tomography scan, which you may be more familiar with as a CAT scan, but either way, this person is receiving a large dose of radiation that can be harmful to their cells. To give you an idea of the radiation dose, if you were to take a plane ride from New York to California, that delivers about half the radiation that an x-ray does, and a CT scan delivers about 100 times the radiation of a single x-ray.