This week we're going to start learning about the anatomy of the heart. The heart is a hollow, muscular, cone-shaped organ, and it's positioned in the thoracic cavity. If we take a look at where the heart is actually located we see the the chest cavity or the thoracic cavity right here on our skeleton. The heart is located just deep to, or internal to this bone, which is called the sternum. So the heart is in this location and that region where the heart is located is called the mediastinum. So I'm going to come over to this model and point out first of all the sternum just so you know for orientation purposes where we are. And then I'm going to take the front wall off this model, and we can see the heart peaking out from between the two lines where it's normal position is in the thoracic cavity. I have our textbooks open to a picture which is showing you a position of the heart in the thoracic cavity and you can see that the heart is enclosed by a membrane layer that's called the pericardium. And, if you look closely, you'll see that the lungs are also suroted, surrounded by membrane layers. This is very common in the body to have internal organs surrounded by membranes which help to anchor the organs in position and protect them. The specific membrane layers that surround and protect the heart, are called the pericardium. So, the heart is located in this region of the thoracic cavity, surround by the pericardium, which is not present on our model. And if we remove the lungs, we get a better picture of the heart's location. This region where the heart is located is called the mediastinum. And we can see that not only is the heart in the mediastinum, but these big blood vessels that enter and leave the heart are present in the mediastinum. In a human, we would expect to see some glandular tissue positioned just over the heart. That glandular tissue is the thymus gland, and also here in the mediastinum we would see nerves and lymphatic vessels. And if I remove the heart, I can see that there are other structures that are in the mediastinum and deep too, or more internal to the heart. Specifically this blue and yellow structure is representing the trachea. And you can see the trachea then divides into two other structures, which are primary bronchi. The trachea and primary bronchi are carrying air in and out of the lungs when you breathe. And then we have this golden brown structure represented on the model. That golden brown structure is the esophagus. Does anybody know what the esophagus does? Natalie. >> It carries food and beverages to the stomach. >> Exactly, yes. So that's also present in the mediastinum. Now if I take a look at this model you can see that the people that developed this model actually included the trachea and the esophagus on the model. So you can see that, you know, as the heart is in position in the thoracic cavity there's structures that are passing posterior to the heart itself. Okay, so now we know location of the heart in the thoracic cavity it's a good time to start thinking about the internal structure of the heart, so that you have a better sense of how the heart can function as a pumping organ. And I want to use this model to describe a little bit about the internal anatomy of the heart. I'll use it because it opens up, so that we can actually see what's going on inside the heart. Now, if I look at this what I see is that there are four different compartments in the heart. And we call those compartments chambers. The two superior chambers, or upper chambers, are called the atria. And the two lower chambers are ventricles. There is actually a wall that separates the two ventricles. We call that wall an interventricular septum. In the same way there's a wall between between the two atria, we call it an interatrial septum, right. And so it, those walls prevent blood in the different chambers from mixing with each other which is very important in terms of the heart's function. Now the first chamber that I want to talk about is this one, which is the right atrium. >> Professor Scanga, you said the right atrium? >> Mm-hm. >> To me, that looks like the left. Could you explain? >> Oh, this is. It's also anatomy. This is anatomy terminology. When we refer to the body, we refer to all of the positions and locations in the body using anatomical position as our point of reference. And so, you know, point out for me where your left hand is. Let's everybody raise their left hand. Okay. You can see that the hand that I'm raising is my left hand. But it's looks like it's on the opposite side, right? So when we refer to anatomical terms we always have to think about them as they would reference our own left or our own right. So this is my right hand, and the right atrium. And if I held this heart in front of Stephanie, she would agree that that's right, okay? So that was a really good question it's very confusing for people as they start to learn anatomy, to keep left and right oriented properly. So we have the right atrium, and the right atrium receives blood that's returning from various parts of the body. The blood coming back to the right atrium is deoxygenated. Now does that mean, do you think Stephanie, does that mean that it doesn't have any oxygen in at all? >> I think that there's some, but not as much if it was oxygenated. >> Exactly. It, deoxygenated blood still does contain some oxygen, but we call it deoxygenated because the blood is not carrying as much ox, oxygen as it could. The reason it has lost some oxygen is because this blood has been out through the tissues of your body and those tissues have taken up oxygen to use them in your metabolism. So, we have three vessels that are carrying deoxygenated blood back to the right atrium. We can see the first of those vessels right here. That is the superior vena cava. Now, who has some idea of what the superior vena cava is doing. Where is its blood coming from? Greg? >> So, it returns blood from the upper extremities and every area above the heart. >> Excellent, excellent. So if we go back over here, we can see the superior vena cava. And we get a sense that it's carrying blood from the head and neck and the upper extremities, just like Greg said. Excellent. Now, the second vessel that's carrying blood back to the right atrium is the inferior vena cava. Where is that blood coming from? Steph. >> The blood from the inferior vena cava is coming from your lower extremities and your abdominal cavity to, back to your heart. >> Exactly. So you can't really see it very well on our torso model, but I can tell you that, that inferior vena cava is right here. And it's carrying blood from all of those lower parts of the body up to the right atrium. There's one more vessel that's carrying blood to the right atrium that you can see right here on the back of this model. That vessel is called the coronary sinus and it's actually carrying blood that has been circulated through the coronary circulation. Has anybody heard that word coronary in terms of blood vessels before? Steph. >> Does that mean it's supplying the heart? >> Exactly. So this blood that is being carried into the right atrium by way of the coronary sinus has been out through the blood vessels that supply the wall of the heart itself. And now that blood is deoxygenated. And it's coming back to the right atrium. [SOUND] Now, after blood flows into the right atrium, then it passes into the right ventricle. The right ventricle has the job of contracting to pump that blood out into this big vessel which is called the pulmonary trunk. What's the pulmonary trunk doing? >> It's supplying the lungs with the blood. >> Yes. So this is the vessel that carries blood into the pulmonary circulation. So this blood is going to go out to the left and the right lung. And when it passes through the lungs, it's going to become oxygenated. You'll notice that when we talked about the superior and The inferior vena cava and the coronary sinus that each of those vessels that I pointed to was a blue vessel. Any vessel that carries deoxygenated blood is represented on models. In a blue color, and that's because deoxygenated blood has a very dark red, almost purplish, color in your body. And, so that blue color reminds us that, that vessel is carrying deoxygenated blood. Oxygenated blood, in contrast, has a bright red color. And so any vessels on that are being represented on models that carry oxygenated blood are always going to be bright red in color. So, think about this for a minute. We've got this blood that was carried through the pulmonary trunk out into the pulmonary circulation. And when it passed through the pulmonary blood vessels, it picked up oxygen. Right? When that blood comes back to the heart, what color will the vessels be that carry the blood back to the heart? >> Red. >> Red, yes. And so we can see back here the vessels that are carrying blood back to the heart we have pulmonary veins and they are represented in red on the model. They are carrying oxygenated blood from the left lung and the right lung back to the left atrium. From the left atrium the blood is going to pass into the left ventricle and then the left ventricle is going to contract and pump that blood into this vessel which is what, Stephanie? >> The aorta? >> Yes. Now the aorta is the beginning of what circulation? >> The systemic circulation? >> The systemic circulation. And what is supplied by the systemic circulation? Steph? >> All of our organs, our muscles. >> Yes. Basically all of the tissues and organs in the body are supplied with oxygen by the blood that's being carried through the systemic circulation, right? And so, after that blood passes through all those tissues and organs, it returns to the heart by way of what vessels? Yes, Natalie. >> The superior and inferior vena cava, and the coronary sinus. >> Exactly, so all of that deoxygenated blood will then return to the heart, specifically to the right atrium. >> Mm-hm. >> By way of the superior and inferior vena cava and the coronary sinus. Excellent! Now, have you noticed yet as we've been talking about the heart, have you noticed anything about the thickness of the atrial walls versus the thickness of the ventricle walls? >> They're a lot thinner. >> Which ones are thinner? >> The, the atria are thinner than the ventricles. >> The walls of the atria are thinner than the walls of the ventricle. Greg, what do you think that means? >> I believe that the ventricle walls are thicker because they have to push the blood with more force out of the heart as opposed to the atria. >> Exactly. So when we talk about the heart contracting to eject blood into the systemic circulation or the pulmonary circulation that requires a forceful contraction of the ventricles, and as a result the ventricular walls also are thicker. Now just looking at this model and seeing the representation of the left ventricle versus the right ventricle, what do you notice about the wall thickness? Steph. >> In the left ventricle, the wall is thicker than the right. >> The left ventricle has a much thicker wall and so that tells you. >> That that must be pushing harder, working more to get the blood into the system. >> Exactly, the left ventricle has to contract with more force than the right ventricle does in order to get blood ejected from the heart.
