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Hypertension and blood vessel damage

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 Tanner Marshall.

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Video transcript

- [Voiceover] So there are a bunch of organs in our body, right? All of which are, well, pretty important to our survival. So, some of these organs are especially vulnerable to, and can be seriously damaged by high blood pressure, or hypertension. Sometimes we call these organs target organs. A few example target organs might be like your kidneys, which help regulate salt and water in your body, or your brain, and your heart. All these organs are pretty important, right? And we definitely don't want them being damaged. But how can they be damaged by high blood pressure? Well, blood pressure is the pressure in your blood vessels, right? And these blood vessels supply the target organs with blood. So if your blood vessels get damaged and can't supply as much blood to your target organs, well those guys are gonna be damaged too, right? Normally your inner wall, or your endothelium of your arteries keep blood moving by staying nice and relaxed, and resisting what we call clot formation. Now, a clot is like this buildup of coagulated blood, which is like, kind of like solid blood. And this is super important for you to stop blood loss by sort of plugging up an area that's losing blood when you get a cut or are bleeding for some reason. Now, it's not good when these clots start to build up inside of the vessels, since they start to make it harder for blood to flow through. Okay, but how can these form? Well, if we're looking at the endothelium, this inner lining of the blood vessel, our blood's always gonna be cruising over the walls, right? And when it does this, it causes a certain amount of stress from friction along the walls, and we call this shear stress. Now, as our pressure in the blood vessels increases the fluid's gonna be pushing harder against the walls as it moves by, and so your force from friction increases and your shear stress increases too. This higher shear stress can start to damage the endothelium, or this inner lining of the blood vessels. Think of like a river flowing along. You've got some trees and shrubs, and maybe some other stuff, maybe, like, an animal standing in it, and they all sort of hang out there without being swept away, right? But what if all of a sudden this huge flood comes through? It starts to take away the trees and the shrubs and animals with it. It's like they're being sheared off the landscape because now that shear stress is way too high. In a similar way when you jam more fluid into these vessels it exerts more pressure radially, or outward, on the endothelium, which makes it want to expand outward. With this higher pressure your shear stress is a lot higher too, and your blood vessel's landscape, just like the river, is damaged. So much so that you start getting these, like, really tiny, microscopic tears in the endothelium. And these tears heal, but they turn into scar tissue, which is fibrotic, meaning that it's like this network of connective tissue. And when this tissue starts to develop, it sort of acts like this net that catches particles like cholesterol, fats, and platelets as they swim by in the bloodstream. When these guys get caught and stuck in the fibrotic net, well, they stay there, and this buildup is called athrosclerotic plaque. Now this plaque takes up space, right? And starts to narrow the blood vessels, and it also tends to make these vessels stiffer, and less flexible. And when they harden like this they can't really relax and expand as much as they could before, and they get even more prone to injury and more buildup. And so as we can see, more plaque means less room for blood, and so less blood gets through these blood vessels to your target organs, like your kidneys, your heart, and your brain. And your blood carries precious oxygen, right? Among other things, and without that, those target organs don't function as well and can be seriously damaged. Additionally, over time, as these vessels get weaker and weaker from higher pressures a bulge might start to form in a weak spot. This bulge is also known as an aneurysm, and can even burst if it's allowed to get too large, which can cause life-threatening internal bleeding. These aneurysms can happen anywhere in the body where the arteries become weakened, but most commonly they happen in the aorta, which is one of your major arteries.