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Pathophysiology of chlamydia

Visit us (http://www.khanacademy.org/science/healthcare-and-medicine) for health and medicine content or (http://www.khanacademy.org/test-prep/mcat) for MCAT related content. These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read or seen in any Khan Academy video. Created by Raja Narayan.

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Video transcript

- [Voiceover] Pathophysiology is the study of how a disease occurs. And so if we're talking about the pathophysiology of chlamydia, we're talking about how this bacterial organism hijacks the cells of our body to multiply and cause an infection. Now the unique thing about chlamydia is that it's not a very powerful organism that carries a lot of its own nutrients. It relies on the nutrients of the host cell that it infects. Which means that chlamydia must live inside of the host cell in order to reproduce and survive. So the way I'm gonna start off designating chlamydia will be in green. So this initial green dot right here actually has a very fancy name. This is referred to as an elementary body. An elementary body. Which is just a fancy way of saying it looks like a dot. So the first step of chlamydia infecting our body is that it needs to somehow enter a cell. And the way that works is because of our white blood cells. So I'll draw this guy right here, make him look rather ferocious with these red teeth right here. Now this white blood cell is similar to most cells in our body in that it has a nucleus. So I'll draw this nucleus up here. And this is where all the genetic information for the cell on how to survive and make proteins is stored. So when a white blood cell sees this elementary body, this unusual particle that shouldn't exist in our body, it wants to eat it. And this process by which this white blood cell swallows the elementary body, or any foreign particle, is referred to as phagocytosis. Phagocytosis. Where if you've heard this term before you might recognize that cyt just means cell and phago is just a fancy way of saying to eat. So this cell is eating this elementary body. And after a nice big gulp, you'll see that the elementary body is now contained within this vesicle. We can also refer to it as a phagosome. A phagosome. Some just means a body that has been eaten, phago. And I just want to point out, I know I drew it as a cartoon here, but the teeth are actually the cell membrane lining of the white blood cell that sort of envelops around the elementary body to turn it into this pocket, this phagosome within the cell. Now, once the chlamydia elementary body is within the white blood cell, it's game time. Now it uses whatever nutrients it has within this dinky little dot, and let me just redraw the white blood cell right here. This dinky little dot will convert from an elementary body to this guy that looks like a star. And because it looks like a star, scientists refer to this as a reticulate body. A reticulate body. and that's just a fancy way of saying reticular, or reticulate means a star. Now once the chlamydia has turned into a reticulate body, it's going to use the nutrients the white blood cell has. So here's our white blood cell, and the phagosome that I'm going to purposely draw larger. And the phagosome will have a lot of reticular bodies, because these will start using the proteins and the machinery that the cell has to reproduce itself with binary fission, meaning it just splits in half. So I'll write that term over here. This is using binary fission, where you take something that grows and just cut it in half and now you've got two smaller versions of it. Binary fission. And while all this is happening, we're directing nutrients the cell should have been using to fortify its cell membrane, to get nutrients from the outside, towards the chlamydia. So you'll notice that it doesn't look like it's doing too well. I'll draw the nucleus very small to indicate that it's not having a great time here. And once we've made enough reticular bodies and we've reproduced enough, the chlamydia will decide that it's time to infect another cell. So here's our white blood cell again. And I'll draw an even larger endosome, it's ridiculous how big it is, and there are these reticulate bodies that are here still that we have reproduced. But in addition to the reticulate bodies, we've started making elementary bodies, these infectious forms of chlamydia. So the elementary bodies are the infectious version of chlamydia, the reticulate bodies are the growth versions of chlamydia. That's a good way to think about it. And so these guys start mass producing within the cell. And the cell is not having a good time now. It is basically on the verge of death because we are not using our nutrients to fortify and grow this cell membrane or to generally help it survive. So as a result of this, the cell will literally pop. It will burst open and rupture. It will rupture and therefor die, causing the reticulate bodies that were converting, as well as the majority of the chlamydia organism now in elementary bodies to be released into the extracellular matrix. To be released outside of the cell. And you'll have some reticulate bodies, of course, but you're going to have a majority of elementary bodies that can be picked up again by another white blood cell and we can repeat this cycle. Another variant of this you might see is instead of a white blood cell swallowing up these elementary bodies, you might have an epithelial cell. So I'll write epithelial cell here. Like the epithelial cells that line the vagina or even line the urethra. That can swallow the elementary bodies by a process known as endocytosis, which is really just an umbrella term for phagocytosis. Phagocytosis is a type of endocytosis. And doing that will produce and endosome. An endosome. And the rest of the cycle is all the same. Especially the very unfortunate outcome right here. So this is how chlamydia will spread from cell to cell and make it's way further up the genital or the urinary tract.