Health and medicine
- Arteries vs. veins - what's the difference?
- Arteries, arterioles, venules, and veins
- Layers of a blood vessel
- Three types of capillaries
- Pre-capillary sphincters
- Compliance and elastance
- Bernoulli's equation of total energy
- Stored elastic energy in large and middle sized arteries
- Compliance - decreased blood pressure
- Compliance - increased blood flow
Learn how compliant arteries allows for a "Constant Pressure System" like a modern water gun! Rishi is a pediatric infectious disease physician and works at Khan Academy. Created by Rishi Desai.
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- does rigid vessels influence the differential between the systole and diastole pressure?(5 votes)
- I found a graph in "The Textbook of Medical Physiology" by Guyton and Hall, that compared normal pressure, to pressure in arteriosclerosis (a condition that would make the vessels more rigid). It showed Systolic pressure increasing greatly, but diastolic pressure remaining about the same. So, the difference between systolic and diastolic pressures would increase.(2 votes)
- At4:15, Rishi says that you wouldn't even notice the difference between systole and diastole, but wouldn't you feel the pressure go up in systole and stillness in diastole (with pressure against your hand)?(2 votes)
- At4:15, Rishi is right. You cannot feel the difference in pressure with your hand because the pressure is not transmitted to the surface of the body from the vessels. What you can feel is the reverberations of the valves closing and the blood slamming against the heart as a result.(5 votes)
- Then where does the blood go in diastole? Rishi says that there's less blood pushing out on the walls, but where does all the extra blood go, the "more" blood minus the "less" blood that is pushing on the wall? Will the blood be more dense in the middle? Pushing out on your hand?(2 votes)
- There is a large bolus of blood initially that cannot immediately end up on the small arteries, capillaries, and veins. After the initial burst in systole, the blood is able to make its way to these smaller parts of the vascular system.(3 votes)
- Would the blood back flow during diastole?
The only reason that the arteries doesn't have back flow is because of the fast moving blood, it doesn't have a chance to turn around.
But because our hand is there, the blood has a chance to turn around. so wouldn't the blood back flow on the aortic valve and since so much pressure is building up, would the valve break?(2 votes)
- There is some retrograde aortic flow in the descending aorta. The pressure wave rebounds off the bifurcation at the iliacs and does put pressure on the aortic valve. Luckily, the aortic valve is strong and typically does not leak. There is a disease (aortic regurgitation) that occurs when the aortic valve leaks and it can lead to lots of problems.(2 votes)
So let's suppose that I take my little drawing of a heart-- I'm going to make it nice and small, so it illustrates the big point-- and I have my aorta there stretched out. And I put my hand right there. Let's say somehow I could get my hand in there, and I could feel the blood pulsing up against my hand. So let's imagine that for a second. Here's the question. What would it feel like? Would it feel like, let's say, this, with each arrow representing systole? Maybe this is when the heart is squeezing here, and the heart is squeezing here and again. Maybe this would be five little spurts of blood? Is that what it would feel like? Because again, in diastole, the heart is resting. So presumably any kind of flow I'm getting would be coming from the heart, right? So is that what it feels like or something else? And we're going to answer that question right now. So let's draw it a little bit larger. I'm going to draw it right here. And you're going to see something very, very cool. So let's say this is the aorta now stretched out. I'm going to draw it like that. And I'm going to keep the center of the aorta here, so you can see what it would look like if it wasn't stretched out. But we know, of course, now that I have compliant arteries and that it will do this. As the blood goes in, this is all going to fill up with blood. And of course, blood is moving through the middle as well. But this is the blood that's pushing out on the walls of the aorta. On both sides, I've got lots of blood pushing out on the walls. And let me draw with arrows how it got there. And of course, I have blood that's going straight through as well. And so here's my blood that's going straight through. And let me draw in my hand, so you can see where that's oriented. This is my hand as before. And I feel the blood going straight through. And that's happening during systole. And then in diastole, you have, we know, recoil. So in diastole, the heart is, again, right here, and the vessels are right here. And they are not as wide or plump as they were before-- something like that. This is the inner tube, if you will, all the way through. And the blood is still in the walls. There's still blood in the walls here. That's the only reason they're pushed out even a little bit. There has to be something there holding it out. And again, on the other side-- but you can see there's a lot less blood than there was. And so you have to wonder, where did all that extra blood go that was in the walls? Or I shouldn't say in the walls-- that was pushing out on the walls? And the extra blood that you don't see is gushing out. So it's actually moving out, and that's pushing out on my hand. So in diastole, I actually have stuff pushing out on my hand as well. And I would feel that. So I would actually feel blood pushing on my hand in diastole. So initially, I thought maybe I would just feel blood in systole, but I actually get flow in diastole as well. And these arrows are a little bit longer because of the fact that diastole, we know, is a little bit longer than systole. Diastole we think is about 2/3 of the time of a heartbeat. And systole we think is about 1/3 of the time in a heartbeat. So what you get, basically, is a continuous flow, a steady stream of flow. And you wouldn't even notice the difference necessarily between systole and diastole. It would be a steady stream. And actually, thinking about steady streams, I'm just going to move this up a little bit because I want to show you something pretty cool. So let's make a little bit of space. And that is that we've actually taken this idea-- and when I say we, I mean toy manufacturers have taken this idea-- and actually made water guns using a similar system. So they actually said, OK, well, we know that people like to spray their friends with water. This is, let's say, a little water gun. And they like to do it after sneaking up on them. If you're like me, you like sneaking up on your cousins. And this is, let's say, the little water chamber. What happens in these water guns that they make is that they have you pump them up. You have to pump up this little air pump. And it actually sends water from this chamber right here over into here. So water goes into this little balloon as you pump it up. So you're pumping, pumping, pumping. Let's say you're waiting for your cousin to come around a corner. You're just sitting there quietly pumping. And this balloon gets bigger and bigger. And it gets very big. And now, you're ready. Now you're ready for your cousin to come around the corner. And let's say at that moment, as you're ready, you see your cousin. You pull the trigger. I just drew a little trigger for you to pull. You pull the trigger, and all this water gushes out. And it comes out in a nice, even flow. It's not like you have to pull the trigger and you get a squirt, and then you pull it again and you get another squirt. You can actually hold the trigger, and you get a nice, even flow just like we have here. So the idea is that you get these even flows by having stored up energy in this elastic balloon, which is right here. So this balloon is actually storing up energy. And in fact, they actually call this a constant pressure system. So think about that. The water gun manufacturers are calling this a constant pressure system. And the idea comes from something that's very similar to what happens in your body-- very, very cool. So when you think about maintaining flow of blood, remember, again, the compliant arteries are really, really helpful for that.