The heart is a muscular organ that contracts to pump blood through the body, and it contracts just like you'd contract a muscle, like the one in your arm. Of course, it's a different type of muscle, and we'll get into the details of that, but it's a similar idea. Now the heart has various chambers in it, and these chambers are called atria and ventricles. The singular of atria is atrium, if you're curious. And ventricles would be ventricle. No special Latin, singular, plural there. So the job of atria is to receive blood from veins, and ventricles receive blood from atria, and also pump that blood into arteries. And separating atria, and ventricles are what are known as atrioventricular valves. These are valves similar to what we saw in veins, and their job is to prevent backflow from the ventricle to the atrium. Blood needs to flow from the atrium into the ventricle, not the other way around. In fact, if blood moves across a valve, this is a bad thing. It's known as a heart murmur, and usually it's due to some type of damage or infection in the valve.
Now between the right atrium and right ventricle is the tricuspid valve. Don't worry about memorizing this name. And on the left, between the left atrium and left ventricle, we have the mitral valve. Again, you don't need to memorize this name. Now there are also valves that prevent backflow from the ventricles to the arteries, and these are called semilunar valves. These, again, are going to be one on the right and one on the left. The valve that separates the right ventricle from the pulmonary artery is known as the pulmonary valve, and the valve on the left that separates the left ventricle from the aorta is the aortic valve. Again, don't worry about memorizing these names. Just know semilunar valves and atrioventricular valves. You just need to understand, sort of, the basic idea behind what their purpose is.
Now, looking at the heart, you can see that in this diagram, right and left are backwards. That's going to be fairly typical because these diagrams are set up as if you are looking at someone's heart. Right? Like you're facing them and looking at their heart. So everything is going to be mirrored. Right? That's why the stuff labeled right is technically on the left side of the page, and the stuff labeled left is on the right side of the page. So the heart has various arteries and veins connected to it that will lead to pulmonary circulation and systemic circulation. The pulmonary artery is going to be part of the pulmonary loop, and it's going to deliver deoxygenated blood from the heart to the capillary beds in the lungs. The pulmonary veins take that oxygenated blood from the capillary beds in the lungs, and bring it back to the heart. So this is all part of our pulmonary loop, or pulmonary circulation, whatever term is easier for you to remember.
Now the aorta is going to deliver that oxygenated blood that's coming from the lungs to the tissues of the body. And the vein that's going to deliver deoxygenated blood from the capillary beds and the body tissues back to the heart, it's actually going to be 2 veins, their plural name for the two of them is vena cava. It's kind of a mouthful. They're basically broken down into what's called the superior vena cava and inferior vena cava. And it's not because one's better than the other; the names superior and inferior come from the fact that one is found above the other. The superior one is located above the inferior one.
So looking at our diagram here, let's just go ahead and trace the path of each loop of circulation. So deoxygenated blood is going to be delivered by the vena cavae. Right here, it's written singular, but, you know, because it it doesn't really matter which one, we're talking about for our purposes. Inferior, superior, both are going to bring that deoxygenated blood into the remember, this is going to be the right side, so it's going to deliver it to the right atrium. The right atrium is going to move that blood into the right ventricle, and the right ventricle is going to send it through the pulmonary artery to the capillary beds in the lungs. From there, the oxygenated blood will be delivered by the pulmonary vein to the left atrium, which is going to move the blood into the left ventricle. And from the left ventricle, it's going to be pumped through the aorta and delivered to the tissues, and that is going to be our pulmonary loop.
And, of course, our systemic loop takes us from the aorta all the way down through these tissues, through all these capillary beds, back up all these veins, and delivers our deoxygenated blood from the vena cava to the right atrium. So these are our two circuits of blood circulation, and they basically each have a purpose to fill. The pulmonary circuit, as we've seen, is there to oxygenate the blood, absorb oxygen from the lungs, and to get rid of the waste CO 2 that gets picked up in the tissues. So the systemic circulation's job is to deliver that oxygen to the tissues, and to pick up that waste CO 2 from cellular respiration, and bring it to the lungs so that the body can get rid of it. So those are our two circulatory loops. Let's flip the page and look at what's going on in the blood.