Welcome to Dr. Warrick's podcast channel. Warrick is a practicing cardiologist and author with a passion for improving care by helping patients understand their heart health through education. Warrick believes educated patients get the best health care. Discover and understand the latest approaches and technology in heart care and how this might apply to you or someone you love. I'm Dr Warrick Bishop and usually I like to welcome you to my consulting room. Today, however, I had an early minute and I've decided to come home and share today's topic with you from home. So on this occasion, instead of welcome to my office, welcome to my home. Today I'm going to talk about the circulation. What is the circulation and how do we understand it? The circulation, if you Google it, you'll get more often than not fairly intricate pictures which show how venous blood returns to the heart and goes to the lungs and back to the heart and around the body and so forth. Sometimes the pictures look a little bit confusing and today what I'd like to do is try and simplify it as best as possible. The better you understand the circulation, the better you can understand what's going on. if things go wrong within the circulation. So in trying to discuss or describe or share with you what the circulation is about, let's start with the circle of circulation. Let's imagine that the circulation is really one big circle of blood flow. I'm going to put to you that if we imagine that the most important component of the circulation is to help us take oxygen from the air and get oxygen to the tissues, then we can think of the lungs as one of the most important components of the circulation. It's taking that oxygen from the air. But the other component of the circulation which is important is taking waste products or carbon dioxide from the capillaries, from the blood vessels within the tissues. So let's think of the circle of the circulation as blood flowing from the lungs, which has blown off carbon dioxide, which has absorbed oxygen and is travelling out to the tissues, where in the capillaries, the smallest blood vessels of the tissues or organs of the body, oxygen is taken out and used by those organs. and carbon dioxide the waste product is absorbed and then that blood with the carbon dioxide in it makes its way back to the lungs and that gas exchange occurs again so here we've got the lungs at the top the capillaries at the bottom and the blood circulating around well that's a pretty simple idea of how the circulation works but let's drill down and understand it a little bit better How does that blood keep going round and round? Well, let's think about the heart as one of the important components because we know the heart is an important pump. The heart has one-way valves in it. And if you think of the circulation as a tube, if you have a one-way valve in the tube and you squeeze... the tube, then the blood can only go one way. It won't come back. So let's think about where the heart fits within the circulation, remembering the heart has one-way valves in it. Again, let's start at our high point, 12 on our clock of the circulation, where the lungs have just undertaken gas exchange. We've now got oxygen-rich blood, which flows from the lungs to the left atrium. I've put a little V in there, that's our one-way valve. Blood from the lungs runs into the left atrium where it gets a squeeze. The one-way valve means that the blood only goes in the forward direction of our circulation. It goes into the left ventricle. The left ventricle is one of the major, or is the major pumping chamber of our body. It also has one-way valves. The ventricle squeezes, the blood can only go one way. It goes forward into the aorta, the biggest blood vessel of the body, coming out of the heart. And that blood vessel then allows the beginning of that circulation process. Blood from the aorta to the organs, blood within the organs to the capillaries. The capillaries, the little or the finest blood vessels where oxygen is taken out and carbon dioxide is absorbed. The capillaries continue to flow and they flow until they become veins and the veins collect together and collect together until they come into two major inlets in the right atrium. The superior vena cava, which is the inlet into the right atrium, which is above the heart. and the inferior vena cava, which is the inlet into the right atrium, which is below the heart. That blood now in the right atrium gets given a squeeze. The one-way valve means it only goes one way toward the lungs in that clockwise direction. The right atrial blood goes into the right ventricle. The right ventricle blood gets squeezed into the lungs. The gas exchange occurs. The blood now runs passively into the left atrium and the circulation continues. Round and round it goes. So that's where the heart fits in in the circulatory process. Let's add in a little bit more, just a bit more detail. So we're building on our initial, our basic understanding. Let's add some organs in there. We start again at 12 o'clock on our clock face of the circulation, we're going in a clockwise direction. Blood from the lungs is drawn into the left otrium, squeezes one-way valve, left ventricle, squeezes out into the aorta. The aorta is the main blood vessel that breaks into the blood vessels that then supply the major organs within the body. Well, the very first blood vessels that come off the aorta actually supply the heart. So, importantly, the heart is supplying the blood to drive the muscle that runs the heart. It's pretty clever when you think of it. The next major organ is the brain. Nearly 25% of the entire circulation of the body goes to the brain. Though there are times when I think some people don't get the full 25%. Sometimes me, when I don't remember things. The kidneys get nearly 25% of the entire circulation as well. They're busy cleaning the blood, drying out impurities and making urine. The gut gets blood, and that varies depending on whether you've just had a meal or not. And of course the muscles get blood, and again that varies depending on whether you're exercising or not. These organs then break down or take the blood and... and take it through smaller and smaller arteries until these arteries get so small they're the fine, very small blood vessels called capillaries, which are so thin and so small that they can allow exchange of oxygen and carbon dioxide through their membranes. It is, of course, at the capillaries that other nutrients and other products within the blood move back and forth as well. But I'm going to stick with oxygen and carbon dioxide because I think that's the simplest thing for us to understand. The capillaries then start to come together and they form veins. There are multiple veins and the veins come together within the organs. And then the organs have veins that all come together and join, as you might imagine, coming together and unifying until all the veins have come together to a large vein. Below the heart that comes into the right atrium, called the inferior vena cava, all the veins come together into a large vein called the superior vena cava that's draining from above the heart. Once the blood's in the right atrium, gets a squeeze, goes forward, one-way valve, into the right ventricle, one-way valve, into the lungs gas exchange occurs. And again, you can see the organs, the tissues, the venous return. So that's really touching on the arterial side of the circulation. Let's have a little think about how the blood gets back from the tissues because there's a couple of tricks associated with that. So here we go. Again, our circular circulation heading in a clockwise direction. Gas exchange occurs. Blood moving through one-way valves through the heart. Blood to the organs, we know it goes to different organs, and then through the capillaries. The capillaries then come together, coalescing and forming veins within those organs. The organ veins then drain and come together until we get large veins that filter back to the heart. I've got some little arrows in here, and they're marking where the muscles sit. some of the return of the blood through the veins to the heart in some of the vessels is through, again, one-way valves, such that external compression on the veins, whether it be one of the large veins of the legs or the veins through the lower part of the leg, Veins get massaged, if you like, by external forces, and because of the long-way valves, the blood flows in one direction. So the veins, as well as the heart, have valves in them to make sure that the blood flow continues in that same direction, that clockwise direction that we've drawn out. As the blood approaches the thorax, it's also important to understand that the thorax, or the chest cavity, helps in that venous return. Every time we take a breath in, we lower the pressure within the chest, which means that blood outside the chest is drawn in. So the returning blood through the veins is assisted by one-way valves and also assisted by the negative pressure within the thorax. Once we've got the blood back into the superior and inferior vena cava, into the right atrium, right ventricle, back to the lungs and around again. So that's really an overview of how the circulation works. I've tried to simplify it as much as I can. I've spread it all out and flattened it so that you can see each stage as it occurs. The value of understanding the circulation is that the better you understand how this process works, the better you can understand how, if there's a particular problem in a particular location, what the effects might be downstream of that. So I'd like to finish that up. I hope you've enjoyed this discussion. I hope you've learned something about the circulation today. I'd really like to thank you for joining me at home and on this podcast. As always, I wish you the very best health. If you have any queries or questions, please drop us a note and let us know if you have any ideas for future podcasts. Again, please feel free to let us know. Take care and bye for now. You have been listening to another podcast from Dr. Warrick. Visit his website at drWarrickbishop.com for the latest news on heart disease. If you love this podcast, feel free to leave us a review.
