So in this tutorial, we're going to look at some of the features of the right side of the heart. We'll start off with the atrium and we'll look at some of the external and internal feature. And then we'll look at the right ventricle and look at some of the features internally and externally.
we'll start off with looking at the right side of the heart. I'm assuming a bit of preliminary knowledge, so you know the basic structure of the heart in terms of the atrium and ventricles and also that you are aware of the great vessels and what these are and the basic function of the heart.
The right side of the heard receives deoxygenated blood and it receives this blood from two great vessels. You’ve got the superior vena cava and the inferior vena cava. And then you've got the coronary sinus at the back which delivers deoxygenated blood from the walls of the heart into the right atrium.
The right atrium contracts and sends blood into the right ventricle through the right atrioventricular orifice. What I've done here is I've just sliced a little bit of the right side of the heart away. We can take a look inside the heart. You can see this opening here.
This is the right atrioventricular orifice, which opens up from the atrium into the ventricle. This is closed by the tricuspid valve when the right ventricle contracts.
The way of remembering, you should know the basic make-up of the heart. You've got the atrioventricular valves and you've got the semilunar valves. The atrioventricular valves, you've got the tricuspid valve on the right and you've got the mitral valve or bicuspid valve on the left.
The way to remember that the tricuspid valve is on the right is that 'tri' has 'ri' in the name whereas mitral doesn't have this. 'Tri', right, it's the right atrioventricular valve. And this closes when the right ventricle contracts. That’s the right atrioventricular orifice opening into the right ventricle.
Within the right atrium, you've essentially got two spaces. They're divided by something called the sulcus terminalis on the external surface of the heart. Internally, this corresponds to the crista terminalis. This structure separates the smooth posterior wall from the ridged muscular, anterior wall. You’ve got these two spaces within the right atrium.
Just taking a look at the right atrium externally, you've got this notable little appendage here. This is the right atrial appendage or the right auricle. This little conical pouch overlaps the ascending aorta. I'll come on to mention that in a bit.
But you've also got something which I've mentioned just now called the sulcus terminalis. 'Sulcus' just means groove. You’ve got this groove on the right atrium. It’s not shown on this model here, so I'll just draw it on very roughly. You’ve got this vertical groove here called the sulcus terminalis. This externally marks the two divisions of the right atrium.
What this line does is it separates the right atrial pectinate muscle from the sinus venarum. What we're looking at here is the smooth posterior wall of the right atrium. This smooth wall is called the sinus venarum. The sinus venarum develops from the sinus venosus of the embryonic heart.
The sulcus terminalis externally represents the line of union between the sinus venarum and the pectinate muscles, so this rough anterior wall.
What I want to do now is we've taken this slice of the right side of the heart. I want you to imagine that we've flapped open the anterior aspect of the right atrium. I'm going to draw on this atrium opened up.
This is the sort of the anterior aspect of the right atrium being flapped open. Internally, corresponding to the sulcus terminalis, we've got something called the crista terminalis. It’s this smooth muscular ridge which corresponds to this line of union between the sinus venarum, the smooth posterior wall and this muscular ridged wall.
On this muscular anterior ridged part, you've got these little muscular ridges called musculi pectinati. I've just drawn them in on here. They're called musculi pectinati or pectinate muscles.
These pectinate muscles extend into this right atrial appendage or the right auricle. You’ve got this smooth posterior wall, which is formed from the embryonic sinus venosus. In the adult, it's known as the sinus venarum.
And then you've got this line of union internally which is called the crista terminalis. This is a smooth muscular ridge.
And then anteriorly, you've got the ridged muscular wall, the pectinate muscles on this anterior wall, which extent into the right atrial appendage.
Remember these sulcus terminalis, which corresponds to the crista terminalis on the external surface of the right atrium, the superior border of this sulcus actually delineates the transverse plane or the horizontal plane where the sinoatrial node resides in the right atrium.
And the bottom of this groove, the bottom of this sulcus, the inferior boundary marks the horizontal plane of the atrioventricular node.
I'll talk about these nodes in more detail in a tutorial on the conduction system of the heart, but it's just something to be aware of.
Just coming back to this sliced heart, between the right atrium and the left atrium, you've got this spectrum called the interatrial septum. If we rotate around the model, this wall here forms this interatrial septum.
And something which isn't shown on this model is the fossa ovalis. This, as the name suggests is an oval-shaped depression and it's essentially a remnant of the embryonic foramen ovale, which in the fetus allows blood to pass from the right to the left atrium. It’s actually open in the fetal heart and you've got this flow of blood from the right to the left atrium bypassing the lungs which aren't actually functional in the fetus. But in the adult, it should be closed. This is the fossa ovalis on the interatrial septum.
And then, you've obviously got the openings of these vessels. Superiorly, you've got the superior vena cava opening into the right atrium. Inferiorly, you've got the inferior vena cava. And just medial to this vessel, you've got an opening of the coronary sinus – so just here. The coronary sinus which drains blood from the muscular walls of the heart into the right atrium opens just medial to the opening of the inferior vena cava.
That’s some features of the right atrium to be aware of.