Hello, hello, everyone! Welcome to another tutorial where, this time, I’m going to be talking about the posteroinferior view of the heart. Don’t be scared. This is an easy topic, but what I’m going to be doing is looking at a perspective, or an aspect of the heart, or a view of the heart known as the posterior and also inferior view of the heart, and then describing all the structures that can be seen from there.
But before we do so, I’m going to show you the anterior view of the heart seen here on the anterior view of the open thorax. Just before we go into more detail, I just want to describe briefly what is the heart. And the heart is a muscle that is responsible for the circulation of blood around your entire body. It is located in a structure known as the mediastinum which is found on the thorax, just behind your sternum. And here, we see the position of the heart in the chest cavity for an anterior aspect as I mentioned.
The heart is a muscle that acts as a pump for the circulatory systems. It is situated in the pericardium, which is the structure right about here that we just cut open. Notice here this structure right about here. We just cut it open so we can expose the anterior view of the heart. And this is known as the pericardium that is a sac-like structure that is also attached to the diaphragm.
With that in mind, a quick intro to the heart, because we could go all day long about the heart, but now, let’s move on to the main topic here, the posteroinferior aspect of this organ.
Now, in the following slides, we will look at the structures visible on the posterior aspect of the heart, more specifically, the posteroinferior view of this organ. Here, the heart is tilted forward, which also allows us to see the diaphragmatic surface of this organ, right about here. And the diaphragmatic surface is formed by both the ventricles, the right atrium, and also with the termination of this vessel here, the inferior vena cava.
Now, let’s talk about or highlight the first structure here, seen on the posteroinferior view of the heart, known as the apex of the heart. Now, the apex is the lowest part of the heart and is found on the left ventricle. It is found or located at the position of the fifth intercostals space on the left or close to the left midclavicular line. So if you were to find or locate the apex of the heart within your chest, this is the coordinates you need to know. And also, you can palpate the heart right here too, then feel the beat.
The apex points downward. If we were to look at… Keep that in mind. If we were to look at the anterior view of the heart, this is where you would locate the apex. It’s pointed downward, protrudes forward and also a little bit to the left, and this is due to the fact that the heart is somewhat position asymmetrically within the thorax. That’s why, for example, your left lung is relatively smaller than your right lung, because your heart is positioned a little bit more towards to the left within your thorax.
The next structure that I’m going to be highlighting right now for you is known as the aortic arch. Now, the aortic arch starts at the point where the ascending aorta ends and then goes all the way to the level of the fourth thoracic vertebra, also known as T4. Now, it is important to mention that it ascends into the arch and goes to the left mediastinum. It is found in front of the right pulmonary artery which is this one right here.
And if I switch the image now, I can show you clearly here the arch. So you have the ascending aorta going up—so ascending, meaning “going up,” where the blood goes, blood flow goes and meets here the aortic arch and then turns into the thoracic aorta, which is the next structure right here.
The aortic arch has different branches, and the first one is seen here, highlighted in green. Now, keep in mind that this one is the first one because the blood flow is coming from the front or the aorta, ascending aorta, which is found on the front of the heart. Now, we’re looking at the posterior view, and then it goes and meets the first branch which is this one here. And this branch is known as the brachiocephalic trunk.
Now, this is also known as the brachiocephalic artery or innominate artery, is the first branch of the aortic arch as I mentioned, and important also to mention that it supplies blood to the right arm, head, and the neck.
The other branch of the aortic arch is this one, also seen highlighted in green, and we call it the left common carotid artery. Now, this is the second branch of the aortic arch, and this artery supplies blood to the head and also the neck. Moving on, we can just uncover and show you the structures here with the myocardium, and now, we can move on to the next one, the next branch known as the subclavian artery. The subclavian artery is the third branch of the aortic arch and function is to supply blood to the left arm.
Now, let’s move the heart a little bit to the left side. So we’re looking now at the lateral left side of the heart where we’re highlighting the next structure that we’re going to talk about, the pulmonary trunk. Now, the pulmonary trunk emerges from the right ventricle—not to be confused with this structure that we just exposed here, just cut here: the wall of the left ventricle, and you can see the inside. But the pulmonary trunk is emerging from the opposite ventricle, the right ventricle. And this trunk is carrying deoxygenated blood from the heart to the lungs.
Now, from the pulmonary trunk, we’re going to have two important arteries coming from this trunk. One is highlighted here in green: the left pulmonary artery. And do not confuse—very careful here. Big highlight—do not confuse or be fooled by the word artery because this structure is going to be carrying deoxygenated blood to the left lung. And you can also see here on the opposite side, you see the right pulmonary artery that will also be carrying deoxygenated blood coming from the pulmonary trunk, then into the left lung or to, in this case, the right lung, right pulmonary artery.
Now, let’s move on to the next structure here. Now, two little structures—not little in comparison to a lot of vessels in your body, but these are known as the left pulmonary veins. And the left pulmonary veins are two veins that carry oxygenated blood from the left lung, and it drains it into the left atrium. Again, do not be fooled by the words veins because this is another exception.
On the heart, there are a few vessels that have exceptions. They are called either veins or arteries, and as you’re used to knowing that arteries will carry oxygenated blood, while veins will carry deoxygenated blood, but this is another exception. So the left pulmonary veins will carry oxygenated blood. And from here, the blood is, then, destined for systemic circulation.
If you have left pulmonary veins, you would sure have these next structures here, the right pulmonary veins, and the right pulmonary veins function in the same way as the left pulmonary veins. These two veins carry oxygenated blood from the right lung and then drain it into the left atrium.
The next structure now seen highlighted a bit further up known as the superior vena cava, and the superior vena cava is one of the great vessels of the heart. It carries deoxygenated blood from the upper extremities of your body and then drains it into the right atrium, as you can also see here on this image. So this is where the blood is going got be drained into.
The superior vena cava is, then, formed by the right brachiocephalic and also the left brachiocephalic veins and begins approximately at the level of the junction of the second and third thoracic vertebrae.
Next structure is also a great vessel, a great vein, and it’s known as the inferior vena cava. And this is or this structure ascends from the abdominal cavity through the diaphragm, entering the chest cavity, then draining into your right atrium. It carries deoxygenated blood from the lower portion of your body all the way back to your heart. You can also see here an image of the inferior vena cava seen from the anterior view.
Let’s move on to the next structure. Now, it’s an atrium known as the right atrium, and this atrium collects deoxygenated blood from the superior vena cava and also from the inferior vena cava as we talked about before. And then they open into the posterior wall of the atrium and the coronary sinus.
Now, still on the right atrium, I have a new image here where I’m showing you the lateral right side of the right atrium, if I were to cut here, and then just pull the wall back, and you can see the inside of the right atrium.
Now, it is important to mention that there are three structures to remember about the right atrium. I just wanted to add them to this tutorial. The first one is the pectinate muscles, and the posterior wall of the right atrium is smooth while the anterior wall is rigid with these muscles, right here, known as the pectinate muscles. The anterior and posterior walls of the right atrium are separated by this structure here known as crista terminalis.
Now, the other structure worth mentioning here, that you can see from this image, is that the right atrium pumps the blood into the right ventricle through the right atrioventricular valve that is also known as the tricuspid, and this is the valve right here—important structures to remember here on the right atrium of the heart.
Let’s go from the right atrium to the next one, the left atrium, seen here highlighted in green. The left atrium makes up the base of the heart. The four pulmonary veins drain oxygenated blood from the lungs into the left atrium as you can see here: the four pulmonary veins draining blood into the left atrium, and also like we mentioned on the previous slides.
Also important to mention about the left atrium, now seen again from the lateral left side from the heart with exposed left ventricle, you can now see that from the left atrium, the oxygenated blood is pumped into the left ventricle that you see here exposed by the mitral valve—this valve right about here, which is a bicuspid valve.
Next structure that we’re going to be covering is now seen here, highlighted in green, and this is the right ventricle. Now, the right ventricle has a triangular shape, and a large part of the sternocostal surface of the heart is formed by its anterior superior border. Its inferior surface rests on the diaphragm, and the right ventricle functions to pump deoxygenated blood to the lungs—through the pulmonary valve first, and then goes into the pulmonary trunk, and then finally, into the pulmonary arteries that will take it to… or take the blood to the lungs.
The walls of the right ventricle are not as thick as those as the left ventricle as you’ve probably guessed because the blood that we’re going to be pumping from the right ventricle is going to go to the lungs—so a shorter trip than the blood that is going to be pumped from the left ventricle that is going to go all the way to the rest of your body.
Now, let’s move on to the next one then: the left ventricle that we just talked about. The left ventricle is also conical, and its apex forms the apex of the heart, as we talked about before. It is slightly bigger than the right ventricle, and its walls are thicker owing to the fact that the oxygenated blood pumped by the left ventricle goes to the systemic circulation.
The next structure that we’re going to be talking about seen clearly from the posteroinferior view of the heart is this one, seen here highlighted in green, known as the coronary sinus. The coronary sinus is a collection of veins joined together to form a large vessel that collects blood from the heart muscle or this muscle that you see here on this image clearly. This is known as the myocardium.
Now, it delivers deoxygenated blood to the right atrium as to the superior and inferior vena cava. And now, I’m going to show you the superior view of the heart. Notice here that this is the anterior view, and we’ve been looking at the heart from this view here, the posterior view. And now, you can clearly see the coronary sinus, also highlighted in green.
The next structure is known as the posterior interventricular sulcus, and the posterior interventricular sulcus is a vertically running longitudinal groove that separates the right ventricle from the left ventricle posteriorly. So as you remember, this is the right ventricle and the left ventricle, now separated by this structure seen here highlighted in green.
Now, this is indeed an important structure because this is where some important blood vessels are going to be passing through. Let me show you now, here on these images of these two vessels: one, seen on the left side, is known as the middle cardiac vein, the one on the right side is the posterior interventricular artery, and these run in this groove.