Internal Anatomy of the Right Atrium and Ventricle

00:01 Now, let's start looking at some of the internal structures.

00:04 There's a lot more to see internally than externally.

00:07 So we'll go one side at a time, and we'll focus just on the right heart to begin with.

00:13 So here we have a nice view of the right atrium, and there's another sulcus here that we haven't mentioned yet.

00:21 And that sulcus is called the sulcus terminalis cordis.

00:25 We throw in the word cordis referring to heart because there's another sulcus terminalis that you'll learn about in the tongue.

00:31 But this is an important landmark for something happening internally.

00:37 So if we were to cut that wall of the right atrium open and reflect it, we can see the sulcus terminalis cordis corresponds with a ridge called the Crista terminalis on the inside of the atrium.

00:53 And this is an important border, because on one side of this Crista terminalis, we have all of these somewhat parallel aligned muscles on the surface of the heart called pectinate muscles.

01:07 Pectin means comb, and they're nice and parallel, like the little teeth of a comb.

01:11 And it's these pectinate muscles, from an interior point of view that tell you you're in the atrial appendage as opposed to the rest of the right atrium.

01:22 And the fact that the rest of the atrium looks smooth compared to this bumpy, pectinate muscle type arrangement of the appendage can be explained by the embryology and they have two different embryologic origins.

01:33 In the cryista terminalis the border between the two.

01:38 As we will eventually see in the ventricles, there is a septum or wall separating the right from the left atrium.

01:46 We call the atrial septum.

01:48 And in this atrial septum, we see a little shallow depression, called the fossa ovalis.

01:56 And a little bit of rem along its superior edge called the Limbus of this fossa.

02:01 And if you saw the fetal circulation video, you'll know that this landmark here is the remnant of what used to be the foramen ovale during fetal circulation, or used to be a hole that blood could pass through to reach the left atrium.

02:18 Usually, that's closed off to become a fossa.

02:22 We can also see a little bit of the tricuspid valve which we'll see more of from the ventricle point of view.

02:28 But before we hit the tricuspid valve, there's a little opening here.

02:33 And this is an opening for something called the coronary sinus.

02:37 And we'll see that the coronary sinus is the major venous drainage of the heart itself.

02:45 We talked about what the heart does in terms of receiving venous blood and pumping out venous blood, but it's an organ, it's a muscle and it needs its own arteries and veins itself and the veins that supply the heart are coming into this region here to enter the rest of the right atrial blood.

03:03 coming from the IVC in the SVC.

03:07 So let's go ahead and zoom in on this area a little bit more.

03:12 Here we see the SVC and the IVC, both entering the right atrium.

03:18 And again, we see the fossa ovalis, the remnant of what used to be a foramen ovale when we wanted some of the blood from the IVC to cross over to the left atrium.

03:28 After birth, it's sealed off so that we have just deoxygenated blood coming from both the SPC and IVC into the right atrium, down to the right ventricle and then out into the pulmonary artery to get oxygenated in the lungs.

03:43 But we have that third source of deoxygenated venous blood coming from the heart itself via the coronary sinus.

03:51 And that's where this opening is.

03:53 We see this opening of the coronary sinus just between the IVC and the tricuspid valve.

04:01 And it has a little bit of a valve covering its opening called thebesian valve.

04:06 That's right up against another ridge of tissue that's called the valve of the IVC or the Eustachian valve.

04:13 And if you've heard the term eustachian tubes and your eustachian tubes are blocked up and you're wondering if it's this same guy is.

04:18 It's the same guy, he was very busy.

04:21 This valve of the IVC, or eustachian valve, though, isn't a valve, like we typically think about other heart valves like the tricuspid valve.

04:30 In the sense that it's not really preventing backflow.

04:33 What it's really doing is well, not much in the adult heart, but in fetal circulation, it was this ridge that guided the IVC blood up through the foramen ovale where we now have a fossa ovalis.

04:47 So it's function as really in fetal circulation.

04:53 If we get down into the right ventricle, and we cut away the portion of ventricle that's not on the septum, called the free wall.

05:02 We can see the inner workings of the ventricle a lot better.

05:07 We can see that the inner surface of the ventricle is thrown into some bumpy ridges, kind of like the right atrial appendage.

05:16 Although they're not quite as parallel, they're a little more haphazard.

05:19 So they're not pectinate muscles, they're called trabeculae carnae.

05:24 We still have a septum here separating the right ventricle from the left ventricle.

05:30 And something that we only have on the right ventricle that we won't see on the left is this circular ridge of tissue, what we call outflow tract or the area leading up to the artery.

05:42 And that's the conus arteriosus or the infundibulum.

05:46 And that means that there's some muscle, this conus muscle between the tricuspid valve and the pulmonary valve, and that's something that we will not see on the left side.

05:58 So again, we have a tricuspid valve as our inflow.

06:02 And we have our pulmonary valve as our outflow.

06:06 Pulmonary valves are very simple and very passive.

06:10 But tricuspid valve because it has to bear the brunt of force of a ventricular contraction has a lot of apparatus attached to it.

06:19 So in addition to the tricuspid valve leaflets here, there are these tenderness cords called chordae tendinae that attach to these finger like projections of the ventricle wall called papillary muscles.

06:32 And they're going to help resist backflow of blood that's being pushed up against the tricuspid valve.

06:38 So if we look at the tricuspid valve from the atriums point of view, it looks pretty simple.

06:44 And I have this soft surface that seems like blood would be easily able to push through on their way down into the ventricle.

06:52 And we have three leaflets as the name tricuspid would imply.

06:57 One up against the septum called the septal leaflet then an anterior leaflet, and a posterior leaflet.

07:04 And we can see those from the ventricle side as well.

07:07 We have the septal, anterior and posterior leaflets.

07:12 Accordingly, we have three sets of papillary muscles.

07:15 Although, they're actually not lined up exactly with the leaflets, they're somewhat in between, so that they have chordae tendinae going to two leaflets instead of just one, but they are located in generally the same area.

07:27 We have a septal papillary. We have an anterior papillary.

07:31 And we have a posterior papillary muscle.

07:35 And an interesting feature of the right side, in addition to the conus arteriosus is this little band of muscle that goes from the septum out to the anterior papillary.

07:46 And it's called the moderator band.

07:49 It's again a unique feature of the right that won't happen on the left ventricle.

07:53 And we're going to see it's important a little bit later in conduction.

07:56 But for now, it's essentially kind of a shortcut for conduction to make sure that the anterior can function the same time as the septal and posteriors.

08:06 Finally, we have the pulmonary valve.

08:09 And it has three leaflets: An anterior, a right, and a left.

08:16 And these are much simpler in structure.

08:19 They're basically little half cups, and it's called a semilunar valve for that reason.

08:24 That can prevent backflow by passive filling and closing up against each other and not letting any blood working its way back into the right ventricle.

08:33 So it's a lot simpler.

08:35 And here from the pulmonary arteries point of view, we can see the anterior, right, and left leaflets.