If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

Intro to hypertension (Pressure, flow, and resistance)

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.

Want to join the conversation?

Video transcript

- [Voiceover] So let's just say that you go in for your annual physical exam, and you're told that you have hypertension. Well what does that mean, and why could this be a problem for you? Well, hypertension is another term we use to describe high blood pressure. So the pressure inside your blood vessels is too high, or the blood that's moving around inside them is under a higher pressure than normal. To sort of illustrate that let's think about your circulatory system instead as like this plumbing system. So you've got a pump that moves water around, the pump being your heart and the water being blood, and the pumps pumping blood out to both your lungs and your body, and then receiving that blood back in. And so the pumping out part are like your arteries going away from your heart, and then the pumping in part are like your veins. And both these pipes, the in and the out, or your veins and your arteries, have a certain amount of pressure. So here going out we have arterial pressure, or pressure in the arteries, and then here coming into the pump we have venous pressure. Since the arterial side is what the heart's pumping out into, if the pressure on that side is too high it gets a lot harder for your heart to pump more blood out. And usually this means the heart has to do more work because it's pumping against higher pressures, right? Now, there are a lot of things that can make the pressure in the pipes higher, and therefore make the pump work harder, but the two main things that we're gonna focus on are called flow and resistance. And the flow is how we describe the movement of a volume of fluid, so how the water moves through the pipes, or in our case the blood circulating around the body. When there's more fluid, or flow, trying to circulate in the same space the pressure's gonna be higher, right? Think of if you turned up the faucet to this system, all of a sudden we're trying to get more water out through the same sized pipes, so now those pipes are gonna be under a higher pressure. But how do we turn up the faucet? How do we get this increased flow, or increased blood volume circulating around the body? Well, it's usually because your kidneys are making you hold onto more fluid, since one of your kidney's main jobs is to regulate the fluid in your body. It could also be because there's more salt in your blood vessels. Fluid tends to move to areas with more salt, so more salt in the blood vessels means more fluid in the blood vessels. And this is also why a diet high in salt can contribute to high blood pressure. Okay, so that was flow. Resistance on the other hand is like how hard it is for fluid to move through the blood vessels. The higher the resistance, just like the flow, the higher the blood pressure. Now, this could simply mean, just like a change in the size of the pipes, and by size I mean diameter. So as the diameter gets smaller you have a higher resistance in the pipes, and so your blood pressure goes up. So think of like a hose that's just open. The water sort of just falls out, right? There's not a lot of pressure pushing it out, is there? Well, what if you put a small nozzle on it? All of a sudden you've got this serious super soaker on your hands, right? That's because the smaller diameter nozzle is putting a lot more pressure on the water. It's the same with a blood vessel that gets smaller. The blood's going to be under a higher pressure. Whenever your blood vessels squeeze, we call that vasoconstriction, and vaso just refers to your blood vessels, so constricting your blood vessels. When the vessels get bigger, we call that vasodilation, because they're dilating and getting bigger. Now, higher resistance could also be caused by your arteries becoming too stiff, which can happen as a result of aging or a buildup of fatty deposits. This buildup is referred to as atherosclerosis. So you've got blood moving through here, and then these buildups start to happen. Or sometimes we just call it plaque, and that plaque accumulates, and in addition to making that opening that the blood can move through in the vessels smaller in diameter, it also makes the blood vessels as a whole less flexible and more stiff. Healthy arteries have a certain amount of elasticity to them, meaning they're a little bit elastic. So maybe when more blood moves through them they stretch just a little bit to allow that additional blood flow. If they loose that elasticity and become stiff then they won't stretch as much and so the resistance goes up, and also your blood pressure goes up.