The Four Heart Chambers and Their Function – Anatomy of the Heart

00:00 Now, here is a little diagram of the circulation, you can see it’s made in two colors - blue for the blood that’s returning to the right side of the heart. It’s exhausted of its oxygen, it’s carrying waste products, particularly carbon dioxide. Carbon dioxide was given off in the lungs, oxygen will be introduced to the red blood cells and then they will get to the left side of the heart where they will be pumped out to the body.

00:25 So, let’s follow the circulation through the heart. You can see that there are two large veins here that drain into the right atrium, the superior vena cava drains the blood from the upper body, the inferior vena cava drains the blood from the lower body.

00:43 They both empty into the right atrium and through… then pass through the tricuspid valve into the right ventricle, they are pumped out through the pulmonic valve into the lungs and then they return through pulmonary veins to the left atrium and then across the mitral valve into the left ventricle and the left ventricle pumps it out through the aortic valve to the aorta and to the whole body. What you see here is a small catheter working its way through the heart. We are going to talk more about that catheter. That’s how we measure pressures and the flow, the amount of blood that the heart is pumping during a diagnostic catheterization. But, again, of course, the blood is not exactly this color blue on the… on the right side of the circulation, it’s a little bit darker and it’s quite bright red on the arterial side.

01:37 Now, here is a more anatomically correct diagram and there are a couple of points I want you to note about that. You will still notice the superior vena cava, the inferior vena cava coming into the right atrium, draining the... if you will, the deoxygenated or tired blood into the right atrium. You can see the tricuspid valve as the blood passes into the right ventricle and then you can see it being pumped out into the pulmonary artery, still all in blue. What’s of interest here is that the left ventricle is a lot thicker than the right ventricle. And in fact, their shapes are slightly different. Why is that? It’s because they have very different functions. The pressure in the lung is quite low, so that the right ventricle functions like a bellows- like the blacksmith uses to create air for his fire that he is going to be melting the… and working on horseshoes, for example. So, it produces large volumes of blood movement at low pressure. The left ventricle, of course, has to pump blood throughout the body, so it has to pump that blood at a much higher pressure. And consequently, the walls of the left ventricle are much thicker than the walls of the right ventricle, it’s functioning not like a bellows, but rather like the piston in a car- a high pressure chamber that does a lot of pressure work as opposed to the right ventricle which does a lot of volume work at much lower pressure.

03:07 Now, here we see the heart diagramed in comparison to the chest x-ray. You can see on the right hand side, this is a so called frontal x-ray like this, and then on the left hand side, there is a lateral x-ray taken like that from the side, and what you can see are several things. First of all, again, notice that the heart is not in the center of the chest, but in fact, is a little bit more in the left chest than the… than the right chest and the bulge that you see down in the… in the left chest is actually the left ventricular outline. If you want to see the right ventricle, you have to look at the lateral view and you see it in front of the left ventricle. Now, people say, “Wait a minute! The heart actually has the right ventricle in front of the left ventricle?” And in fact, that is exactly the case. We will see that on some further x-rays and Magnetic Resonance Image which will show you that, in fact, the right ventricle does lie in front closer to the breast bone than the left ventricle which lies a little bit behind. And you can get a hint of that from the… the two diagrams here that are reflecting what you see in the chest x-rays below.

04:26 Now, here is an MRI of the chest. What’s at the top there is the front, the breast bone and what’s at the bottom of the picture is the spine, you can see a little area of the spinal vertebra there, and you can see the heart right in the middle there of… of the diagram labeled; RV is the right ventricle and LV is the left ventricle and you can see that the right ventricle is lying in fact, in front, that is closer to the chest front wall compared to the left ventricle. And again, here is again the diagram showing you where the heart is located and also, where the different points are that you can best hear with your stethoscope, the sounds made by the four heart valves. We are going to talk about those in… in just a moment. But, you see their areas on the little bit upper right chest, little bit upper left chest, lower right chest and lower left chest.