Definition, function and anatomy of the right atrium.
Hello, everyone! This is Joao from Kenhub, and welcome to another anatomy tutorial where, this time, we're going to be covering the right atrium and ventricle. And to do so, we’re going to be using 2 images. This one that you see now on the screen where we’re going to then show you the right side of the heart. We just cut open the right atrium, exposing the different structures that you find there on the right atrium. We’re also going to show you this image that you see now on the right side where we do the same thing but this time we’re looking at the anterior view of the heart and we just cut open here the right ventricle, as you can see here, to expose the different structures that we’re going to be highlighting and discussing throughout this tutorial.
And let’s start with the very first one that you see here highlighted in green – one that I talked about before – yes, this is the right atrium that you’re seeing right now. And this is receiving – this part of the heart – receives deoxygenated blood from the superior vena cava which you can see here on this image – this is the superior vena cava – also receives deoxygenated blood from the inferior vena cava, which you also see here. And the right atrium receives deoxygenated blood from the coronary sinus, the anterior cardiac vein, and also the smallest cardiac vein. So, all of those structures will be taking blood, deoxygenated blood, into the right atrium. And once the right atrium receives deoxygenated blood from these vessels, will be pumping it into the right ventricle through the next structure that we’re going to be highlighting now on the screen in green, you see, the right atrioventricular valve also known as the tricuspid valve.
This valve is found on the right dorsal side of the heart between the right atrium and the right ventricle. The normal tricuspid valve will usually has 3 leaflets and 3 papillary muscles. They are connected to the papillary muscles by these strings here that you see known as the chordae tendineae, which lie in the right ventricle. Now, tricuspid valves will not always consist of 3 leaflets. They may also occur with 2 or 4 leaflets, the number may change during one’s lifetime.
You can see here clearly now from this image of the anterior view of the heart, the tricuspid valve highlighted in green but this time we’re seeing it from then the right ventricle. Now, this structure will have a role, a very important role, and the function of this valve is to then prevent backflow of blood into the right atrium. So, once the blood reaches the right ventricle, you don’t want it to go back to the right atrium. So, this valve has an important function to prevent that from happening.
The next structures that I would like to highlight here which I already talked about briefly – these are the heartstrings, the chordae tendineae. In other words, the tendinous cords or heartstrings. They are cord-like tendons that connect the papillary muscles to then the tricuspid valve. So, as you can see here on these images, the chordae tendineae are attaching here to the papillary muscles – these projections that you find here on this image – to then the actual tricuspid valve, this white structure that you see here on the image. Now, these structures are 80% collagen while the remaining 20% is made up of elastin and endothelial cells.
Going back to this view of the heart where we can see the right atrium, we’re highlighting a structure known as the fossa ovalis of the heart. Now, the fossa ovalis is a depression that you find in the right atrium of the heart. Now, this structure has an important role. During fetal development, the foramen ovale is a connection that allows blood to flow from the right atrium into the left atrium in order to shortcut the undeveloped lungs. Then, at birth, the foramen ovale will be closing with the first breath of the baby and the fossa ovalis will remain. And, on this picture, we’re looking at an adult heart and you can see the remains, the fossa ovalis of the heart, the structure highlighted in green.
Now, the next one that we’re going to be highlighting is this rim around the fossa ovalis which is known as the limbus of the fossa ovalis. It is clearly a prominent oval margin of the fossa ovalis. It is mostly distinct above and at the sides of the fossa. Below, it is almost nonexistent as you can see here - we’re not highlighting this portion – which means that you can barely see any limbus on this area, just below the fossa ovalis.
The next structure that we’re going to be highlighting here which you see here on this cut, this is known as the right atrial appendage or the right auricle. This is a pouch-like extension of the muscular part of the right atrium that pumps blood to the right ventricle during atrial systole or ventricular diastole. Now, you can also see the right atrial appendage here from this image of the anterior view of the heart.
The next structures that we’re going to be highlighting here on again this image of the open right atrium, you see here the pectinate muscles. These are clearly seen here as parallel ridges in the walls of the atria of the heart. Behind the crest of the right atrium, the internal surfaces is then smooth. The pectinate muscles, they make up the part of the wall in front of it. These structures also have an important role. Some sources cite that the pectinate muscles are useful in increasing the power of contraction without increasing heart mass substantially.
Next, we’re going to be highlighting this rim here which is known as the crista terminalis. It is a smooth muscle ridge in the superior portion of the right atrium and the role of the crista terminalis is to divide the pectinate muscles and also the right atrial appendage from the smooth surface of the right atrium.
Next structures we’re going to be highlighting here – this is an orifice – we just removed the tricuspid valve to show this orifice which is known as the right atrioventricular orifice. So, this is basically an opening. Known also as the right atrioventricular opening. This is a large oval aperture of communication between the right atrium and ventricle. Now, this structure is located at the base of the atrium and it measures about 5 cm in diameter and surrounded by a fibrous ring covered by the lining membrane of the heart. It is considerably larger than the corresponding aperture that you find on the left side of the heart being then sufficient, you can actually fit the ends of 4 of your fingers. It is guarded by then the tricuspid valve that I just removed here on this image to then just expose this opening so you can clearly see how it communicates and makes this communication between the right atrium and right ventricle.
We’ve been talking about this structure that you see here highlighted and I talked about before in the first slides, this is the right ventricle highlighted in green, and we’re looking at it from the anterior view of the heart. Now, the right ventricle will be receiving deoxygenated blood from the right atrium and then it pumps this blood into the pulmonary trunk which is the structure here which then takes it to the different pulmonary arteries, the right one and the left one. Now, this blood goes then into the lungs where it gets re-saturated with oxygen.
Now, we’re going to highlight here this entrance which is known as the conus arteriosus. It is a conical pouch formed by the upper and left angle of the right ventricle of the heart from which then the pulmonary trunk arises. The conus arteriosus is also called the infundibulum and it has a role. Now, it is then the entrance from the right ventricle into the pulmonary trunk as I mentioned before.
Just a bit above, you’re going to find the next structure highlighted here in green which is known as the pulmonary valve. Now, the pulmonary valve is positioned at the transition from the conus arteriosus and the structure that I pointed out before – this structure here – which is then the pulmonary trunk. The pulmonary valve is a very important structure because it prevents blood from flowing back into the right ventricle during diastole. Now, this valve has 3 cusps and opens during ventricular systole when the right ventricle pumps blood into the pulmonary arteries. Closure of the pulmonary valve contributes to the second heart sound, the famous lub-dub. In this case, the second heart sound would be the dub.
Next, we’re going to be back on this image to show you here highlighted, the right pulmonary artery, which you can see here just for a bit of location. We’re standing what you can see here. Now, the right pulmonary artery is longer and also larger than the left. Now, the right pulmonary artery takes deoxygenated blood to the right lung. But if we look here at the anterior view of the open thorax as you can see highlighted now in green, you see the right pulmonary artery. Now, this one is longer and larger than the left one which you can also see here on this image – this is the left pulmonary artery – and as you can see runs horizontally to the right behind the ascending aorta which you can also see here – this is the ascending aorta – and also behind the superior vena cava which you can also see here on this image.
Now, the right pulmonary artery is also in front of the right bronchus which you cannot clearly see here on this image. You just see here a bit of the left one and also in front of the root of the right lung where it divides into 2 branches.
Now, we’re ready to move on to the next structure that you see here now from an anterior view of the heart. We’re seeing the supraventricular crest. Now, the supraventricular crest of the right ventricular is a round accentuation of its muscular wall. It extends between the pulmonary orifice inferiorly and to the right of the atrioventricular orifice. It has a role and the role of the supraventricular crest is to separate the conus arteriosus from the rest of the cavity of the right ventricle. And as you can see here, we only see a little cut here of the supraventricular crest because we just removed a bit of the wall of the right ventricular.
Next structure that we’re going to be talking about as you can see here on these 3 images of the anterior view of the heart. You notice here these structures that I talked about before highlighted in green, these are known as the papillary muscles. Now, you can see here the anterior papillary muscle on the far left, then in the middle you see the posterior papillary muscle and on the far right you see the septal papillary muscle highlighted in green. The papillary muscles are located in the ventricles of the heart and they attached to the cusps of the atrioventricular valves both the mitral valve that you find then on the left side of the heart and the tricuspid valve that we just see here on the image here on the right side of the heart and they attached via the chordae tendineae. As for the different roles of the papillary muscles, they are able to contract to then prevent inversion or prolapse of the mitral or tricuspid valves.
Next structure we’re going to be highlighting here back to this image of the lateral view of the heart here with the opened atrium, right atrium, you see this highlight which is the orifice of the coronary sinus. I can show you here. This is the orifice of the coronary sinus. The orifice of the coronary sinus is the location where the coronary sinus enters the right atrium. It is then positioned next to the orifice of the inferior vena cava which you can also see a bit here and is closed by the valve of the coronary sinus which you also see here and which will be the highlight of the next slide.
Now, the valve of the coronary sinus, it is also named after the German anatomist, Adam Christian Thebesius, we also, we can also call it the Thebesian valve. Now, this is a semicircular fold at the orifice of the coronary sinus and the function is to prevent blood from flowing back into the coronary sinus during atrial contraction. However, the valve varies inside and can also be absent.
Next on our list, we’re going to be highlighting this structure here which shows the interatrial septum. Now, the interatrial septum is a thin tissue wall that separates the 2 cardiac atria. This is a good part to add a clinical point here about atrial septal defect which is usually a common point that is made in different classes in anatomy. While the atrial septal defect is a relatively common heart malformation that will be occurring when the interatrial septum, this structure that you see here highlighted in green, fails to develop properly.
Now, I would like to show you here another image from another view of the heart where you can see here this is the open left atrium and also here the open cut left ventricle. Now, you can see from the other side highlighted in green the interatrial septum just between, forming a wall between the 2 atria.
Moving onto the next structure that we’re highlighting here on the anterior view, you notice here this is the coronary sulcus. This structure is a circular indentation between the atria and the ventricles on the outside of your heart where the coronary arteries are then located. You can also name it coronary groove or atrioventricular groove.
The next structures that we’re going to be highlighting have an interesting name, the trabeculae carneae. Now, these structures are round columns of muscle tissue that are spread all over the inner surface of the heart ventricles except for the conus arteriosus. Their function is to then decelerate the incoming blood by causing swirling motion inside the blood flow of the ventricles. This also increases the efficiency of the ventricles pumping process.
Next structure that we’re going to be highlighting here is this one that is known as the septomarginal trabecula. In the right ventricle, you can find the septomarginal trabecula which is a piece of cardiac muscle tissue that belongs to the trabeculae carneae. Now, it runs from the anterior papillary muscle towards then the interventricular septum. The septomarginal trabecula is a structure in the right ventricle that was already represented in the drawings of the famous artist and scientist, Leonardo da Vinci. For this reason, it is also called the Leonardo’s cord. It is believed that the septomarginal trabecula assists in the electrical conduction of your heart.
Few other structures worth noting here, this highlight, this is known as the inferior vena cava and this is a large diameter vein that carries deoxygenated blood from the lower half of your body to the heart’s right atrium. To be more specific, it receives blood from your legs, pelvis, and abdominal region and then takes it into the right atrium.
If we move on and see here on this image, you can also see here highlighted the inferior vena cava and how it is connected to the right atrium. And speaking of inferior vena cava, we’re going to highlight this structure which is the valve of the inferior vena cava. This valve is also called the Eustachian valve surrounding the orifice of the inferior vena cava and is a relic of fetal development. Now during fetal life, the Eustachian valve directs blood towards the foramen ovale in order to lead the blood directly from the right into the left ventricle. And, at birth, the foramen ovale as I mentioned before will be closing with the first breath of the baby and, thus, the Eustachian valve will be losing its function.
We’re also going to be finding this vein here, which is then the superior vena cava, and this one will be transporting deoxygenated blood from the upper half of your body to the heart’s right atrium. To be more specific, it’s going to be receiving blood from other 2 main veins known as the brachiocephalic and azygos veins. If we move on to this image here of the anterior view of the heart, you can still see highlighted in green, the superior vena cava.
Moving on, I would like to still show you other structures, other important structures, that we’ll find here on this image that I would like to pinpoint before we terminate or finish this tutorial. Now, these structures include, this one here that you see highlighted in green, these 2 are known as the right pulmonary veins. The pulmonary veins are going to transport oxygenated blood from the lungs towards then the left atrium of the heart so it can get pumped back into the whole body. These veins are quite exceptional when compared to other veins in the human body. They do not have valves. Now, the right pulmonary veins can be also divided into a superior right pulmonary vein which you can see here, and then below, you’ll find the inferior right pulmonary vein.
So, using these images you can find this structure here which is on the other side, and then the left atrium. The left atrium, as a reminder, it receives oxygenated blood from the pulmonary veins and then pumps it into the left ventricle via the mitral valve. We will be covering this structure in a bit more detail on a separate tutorial.
Next, I also would like to briefly cover this one that we talked about – we saw this image before – this is highlighted, the left ventricle. Now, in diastole, the left ventricle will be receiving oxygenated blood from the left atrium. When systole starts, the muscle cells contract in order to pump blood into the aorta and thus into the entire body. And if we look again at the image of the anterior view of the heart, you can see here highlighted, the left ventricle.
Finally, the last structure that I’m going to be highlighting here, this is the ascending aorta. Now, the ascending aorta is technically the very first part of the aorta which comes out of the heart. It starts at the left ventricle and then becomes this arch that you can see here on the image, the aortic arch. This part of the aorta only has 2 branches, the 2 coronary arteries which you see one here – this is the right coronary artery. But if I show you here this image where we just have a cut of the aorta, you can clearly see here the right coronary and the left coronary artery – the 2 branches of the ascending aorta.
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