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Voiceover: You'll very rarely hear anyone say that the patient has leukemia. Instead, they're more likely to say something like the patient has acute megakaryoblastic leukemia. So, what do all of those other words mean? Well, to understand that we'd have to go back to this diagram, which at this point is probably showing up in your dreams, because of how many times I've used it, but we're going to use it this time to show how the different leukemias are divided, how they're split up and organized. So, the first thing I'm going to do is, I'm going to divide this diagram in half. I'm going to divide it in half horizontally. So, I'm going to draw this line down the middle, and that would split up the cells according to how mature they are, right? So, you'd end up with a row of cells on top that has the most immature blood cells that you could possibly have and a row of cells at the bottom which has some still immature cells, but these cells are a little bit more developed, a little bit further along. So, this is actually the first way that you can split up the leukemias. If a leukemia comes from one of these cells up here, it's called an acute leukemia, and if it comes from one of these cells down here, it's called a chronic leukemia. So, the first way to split up the leukemias is by how immature the originating cell is. So, what do the words acute and chronic have to do with maturity? That seems like a really random word choice, right? Well, it's actually not, because acute leukemias, turns out they grow very fast, they grow very fast. So, a person with an acute leukemia can start to feel sick, can start to show signs and symptoms within weeks, not years but weeks of the leukemia forming. So, it's a very acute onset of disease, okay? Now, chronic leukemias, turns out they grow very slowly. So, a patient with a chronic leukemia can sometimes go years without having any symptoms at all. So, it's a very chronic onset of disease. So, I just want to clarify, guys, that the whole process by which the leukemia occurs is still the same. So, we still have this immature blood cell that loses the ability to mature and then starts dividing rapidly and out of control. That's still going on, but what we're doing now is we're fine-tuning what we mean by the word, immature. So, we're asking the question, just how immature is that blood cell? And so, I want to go back to the diagram that we used to show how leukemias occur. So, we said that this is what normal blood cell maturation looks like, right? And this is what happens when leukemia occurs. So, you have this blood cell that's stuck. It's arrested in the immature state, and it can't move any further, and then it starts to divide really rapidly and out of control. So, look at the leukemia cells. Since they're in the first stage of development, they're the most immature blood cells that you could possibly have. This must be a picture of acute leukemia. So, let's compare that with what chronic leukemias look like. So, a chronic leukemia picture looks more like this, where you still have these blood cells, these immature blood cells that are arrested in their maturation, they can't move forward, and they start dividing really rapidly. The only difference is, is that this time the leukemia cells are a little bit more developed. They're at the next stage of maturation, and not only do these chronic leukemia cells divide really rapidly, but they also live longer than the average normal blood cell does. So, there's a degree of immortality that these chronic leukemia cells have. So, this is a picture of chronic leukemia. Now, something else that I think this diagram does a pretty decent job of illustrating is that when you have an acute leukemia, your leukemia cells look nothing like your mature specialized cells. I mean, they bear no resemblance whatsoever, and we said before that these cells perform almost no function. They're just kind of like a waste of space versus if you look at your chronic leukemia cells, they don't look exactly like your mature specialized cells, but they certainly resemble them just a little bit more, right? And in terms of their function, they leave a lot to be wanted, but it's not unreasonable to say that they can do a couple of things correctly. You know, they won't do everything, but they can do a couple of things correctly. So, this is the first way you can split up the leukemias, acute versus chronic, where acute leukemias come from the most immature cells, chronic a little bit more developed, a little bit more mature cells. Acute leukemias grow very rapidly. Chronic leukemias grow slowly. And acute leukemia cells bear no resemblance in appearance or in function to the mature specialized cells versus chronic leukemia cells resemble the mature specialized cells a little bit more, in terms of appearance and what they're able to do, okay? So, now let's talk about the second way you can split up the leukemias. And so, this time we're going to take this diagram, and we're going to split it in half vertically, and if we did that, we drew a line down the middle, we'd be splitting up the cells not according to how mature they are but according to what cell type, what type of cell they are. So, you'd end up with the myeloid cells over here and the lymphoid cells over here, and you can leave things as broad as myeloid versus lymphoid, or you can specify a little bit more about what cell lineage, particular cell lineage you're talking about. So, this is the second way that the leukemias are split up, according to cell type. So, I want to go back to that first example that I gave you in the beginning of the video, acute megakaryoblastic leukemia. What cell does that leukemia develop from? Well, if we're talking about acute, it must come from this row over here, right? And we said acute megakaryoblastic, so that must be this cell right here, this cell right here. So, an acute megakaryoblastic leukemia comes from this cell right here. So, let's take another example. What about chronic lymphocytic leukemia? So, chronic means that it must come from one of these cells down here. Lymphocytic must be pointing to either this cell or this cell, right, one of the lymphocytes. And you can leave it as broad as that or you can specify whether you're talking about a B lymphocyte or a T lymphocyte, okay? So, that's how all the leukemias are split up. Now, we're ready to go into the details about the different leukemias.