Okay! So now, we’re taking a look at some of the features of the right ventricle. You can see in this position in the anatomical position, the right ventricle here actually forms a lot of the anterior surface of the heart because of the way that the heart is angled in the mediastinum.
When the right atrium contracts, blood is send into the right ventricle through the atrioventricular orifice. When the ventricle contracts, the right ventricle contracts, the back flow of blood is prevented by the tricuspid valve which sits in this atrioventricular orifice and prevents the back flow of blood.
I’ve just dissected away the wall of the right ventricle and we can see this tricuspid valve here. It’s called ‘tricuspid’ because it has three cusps. It’s got an anterior, posterior and a septal cusp. The septal cups is called ‘septal’ because it’s closer to the ventricular septum, so it’s on the septal side.
At the base of these three cusps, you’ve got this fibrous ring which surrounds the atrioventricular orifice. This fibrous ring gives support to this orifice. That’s like the base of these three cusps.
And then as you can see, these cusps have these cord-like structures coming from them attaching them to this muscle. These cords, which I’m highlighting here in yellow, are called chordae tendineae. They attach to the tip of these muscles here which are called papillary muscles.
The point of the chordae tendineae and the papillary muscles is to prevent these cusps, to prevent the tricuspid valve from being averted back into the right atrium when the ventricle contracts and the pressure increases and the back flow of blood forces against the tricuspid valve.
Just to show you more diagrammatically, imagine these two blue structures are the cusps of the tricuspid valve. When the ventricle contracts, the pressure in the right ventricle increases a lot, so the blood is forced backwards. The pressure against these cusps, if they want attachments to the papillary muscles via this chordae tendineae, the cusps will be averted and that would be forced backwards into the right atrium like this by the pressure of the blood and the blood would then flow back into the right atrium.
The papillary muscles, by attaching themselves to the cusps of the tricuspid valves via these cords, the chordae tendineae, they prevent this from happening. They thereby prevent the backflow of blood into the right atrium when the ventricle contracts.
Just going back to this view here, you’ve got three cusps and you’ve got three papillary muscles. You’ve got a posterior, an anterior and a septal cusp and you’ve got corresponding papillary muscles. You’ve got a posterior and anterior and septal cusps, sorry - papillary muscles.
The anterior papillary muscle is the biggest muscle and it attaches to the anterior wall; the septal papillary muscles, a bit variable. Sometimes, they’re very small and sometimes, they’re even absent. In this case, the chordae tendineae arise directly from the ventricular wall.
Within the right ventricle, you’ve got other muscular structures like the papillary muscles except they’re not free at one end attaching to chordae tendineae. They’re either fixed at both ends and free in the middle or they’re fixed entirely along their length. These muscular columns, these round muscular structures in the right ventricle are called trabeculae carneae.
I’ve just switched over to this section of the right ventricle. You’ve got part of the tricuspid valve chopped away, but you can see the papillary muscles sticking up with their free end attaching to the chordae tendineae and the chordae tendineae attaching to the cusps of the tricuspid valve.
Within the right ventricle, you’ve got this trabeculae carneae, which are rounded muscular columns. I’ll just draw a quick diagram to illustrate this.
You’ve got the papillary muscles which are free at one end and attached to the chordae tendineae. And then you’ve got the trabeculae carneae, which are either fixed along their entire length – so they’re fixed like this. If you imagine, this is the ventricular wall here and this is the inside surface with the papillary muscles and the trabeculae carneae attaching to them.
You’ve got three types. You’ve got the papillary muscles, which are free at one end. You’ve got this type of muscular column, which is fixed along its entire length. And then you’ve got some which form kind of like bridges, so they’re fixed at both ends, but they’re free in the middle.
Like you’ve got the musculi pectinati in the right atrium, you’ve got the trabeculae carneae in the right ventricle.
These are found in the inflow tract, but the outflow tract is slightly different and it’s smoother. It’s called the conus arteriosus. You can see the outflow tract here leading into the pulmonary trunk. And this is called the conus arteriosus or the infundibulum and it forms the outflows tract of the right ventricle.
And if I rotate the model slightly further around, you can see these cusps here. You’ve got these three semilunar valves, which form the pulmonary valve. This valve is found at the apex of the infundibulum or the conus arteriosus and it closes off the opening to the pulmonary trunk.
If I just rotate the model around, you can see the external surface of the heart. You can see the pulmonary trunk dividing into its right and left branches.
Just switching back to this model here, if I dissect away the outer layer of the pulmonary trunk, you can see a clearer view of this valve, this pulmonary valve. It’s got three leaflets, three cusps which make up this semilunar pulmonary valve.
What I'm going to do now is I'm just going to switch over to a diagram and we're going to take a look at a transverse section about this level. We’re going to look down at the configuration of this valve.
We’re looking down at this horizontal section. You can see the right atrium at the back, you've got the right auricle here and this is anterior. You can see the pulmonary valve here and you can see the three leaflets. The pulmonary valve has three semilunar cusps.
This diagram here just illustrates a dissection of the pulmonary trunk with the dissection flattened out. We’ve opened up the pulmonary trunk and flattened out this valve, so you've got the three cusps in a row.
Down here, you've got the outflow tract of the right ventricle. Up here, you've got the lumen of the pulmonary trunk. You can see that the three edges of these three cusps of the pulmonary valve project into the lumen of the pulmonary trunk. And at three edges, you've got a bit of the thickening of the cusp, which is called the nodule of the semilunar cusp. You’ve got this thickening here.
You’ve got three cusps – a left, a right and an anterior cusp. And then you've got these pockets formed by the cusps. These pockets here are called the pulmonary sinus. When the ventricle contracts, you've got blood shooting out through the valves. But during relaxation, blood returns and it fills these sinuses and it ends up causing the pulmonary valve to close and prevent backflow of blood into the right ventricle and outflow tract and ultimately, back into the right ventricle.
Just coming back to this diagram, you can see the configuration of the pulmonary valve and you can see these sinuses here which fill with blood and cause the valve to close when the ventricle is relaxed.
Just coming back to this model here of this dissection, one last thing to mention is the interventricular septum. This is the structure that separates the left ventricle from the right ventricle.
This diagram here shows it quite nicely. You've got this interventricular septum separating the right side of the heart from the left side of the heart. And it consists of two parts. You've got this thick muscular ventricular septum, which forms most of it. Most of this septum is thick and muscular.
But then you've got this little bit at the upper part and posteriorly, which is called the membranous ventricular septum. This is thin and fibrous. You’ve got the membranous and the muscular ventricular septum.
And the last thing to mention is that coming off the interventricular septum; you've got this specialized trabeculum. This is called the septomarginal trabecula. You can see it here. It comes off the septum and it actually attaches to the base of the anterior papillary muscle.
This specialized structure is quite important because it actually carries some fibers of the conduction system of the heart. It carries the right bundle of the atrioventricular bundle to the anterior wall of the right ventricle. This is called the septomarginal trabecula. It's attached at one end to the ventricular septum and at the other end to the base of the anterior papillary muscle.
Those are some of the key features and structures of the right ventricle.