Internal Anatomy of the Left Atrium and Ventricle

00:01 Okay, now let's take a look at the internal structures of the left side of the heart.

00:07 Having seen the internal structure of the right heart, that should be a lot easier, although it's not exactly the same.

00:13 And there are some key differences that we'll point out along the way.

00:17 So here again, is our left atrium.

00:20 And if we faded away, we can see our atrial septum, This time from the left, and the left atrium also has an appendage.

00:29 Although, it looks different from the right.

00:32 It's smaller. If it's more narrow, and it's longer than the right appendage, which tends to be larger and more broad.

00:41 The left atrium is receiving pulmonary veins.

00:45 And it's going to go through a valve similar to the tricuspid, but slightly different.

00:51 And that's going to be called the mitral valve.

00:55 So if we look at a cross section along the long axis here, we can see the free wall of the left ventricle, and the ventricular septum.

01:04 And the left ventricle has trabeculae corneae, just like the right side did.

01:09 Although they tend to be less prominent and not quite as tall as they are on the right.

01:15 And where our mitral valve has leaflets and other structures that look very similar to the tricuspid valve.

01:22 In the sense that we have papillary muscles, and we have chordae tendinae.

01:27 The only difference is we only have two leaflets and two capillaries instead of three.

01:34 If we look at the mitral valve from the atriums point of view, it looks like it's very happy to see us.

01:40 It looks like it's smiling there.

01:41 And above that smile from our point of view, that's our anterior leaflet.

01:47 And below, that's our posterior leaflet.

01:50 Again, we only have two.

01:52 In fact, you would think tricuspid and bicuspid would be better than tricuspid and mitral.

01:56 I don't know what to tell you. We just call it mitral.

01:58 Sorry, it has two cusps though.

02:01 If we look at the mitral valve from the ventricle side, we can see the anterior and posterior leaflets.

02:09 And the two papillary muscles, again are named for their location, not really which leaflet they attach to.

02:17 Both of them have chordae that attached to both leaflets.

02:20 It's just that one is more anteriolateral.

02:24 So it's the anterolateral papillary muscle.

02:26 And the other is more posterior medial.

02:28 So it's the posterior medial papillary muscle.

02:34 One thing I mentioned on the right that we don't have on the left was that conus arteriosus, or infundibulum, between the tricuspid and pulmonary valves.

02:44 Here, we don't have that gap between the mitral and aortic valves.

02:48 Here, the mitral valve and aortic valve at a certain point are in what we call fibrous continuity.

02:54 So there is no conus here.

02:56 And embryologically speaking, it's the presence of a conus on the right and absence of the conus on the left, that actually makes sure that the pulmonary lines up with the right ventricle, and the aorta lines up with the left ventricle.

03:13 The aortic valve is another semilunar valve, just like the pulmonary valve.

03:19 And when you see them side by side, they look very similar to each other.

03:23 And they're also right next to each other.

03:26 Again, that reflects the embryology because they began as one single mega artery called the truncus arteriosus that just got divided right down the middle.

03:35 So it's no surprise that they look like mirror images of each other.

03:39 That division of a single artery resulted in anteriorly, there being a pulmonary artery and posteriorly, there being an aortic valve.

03:49 If we look at the leaflets of the aortic valves, we see their names slightly different because of their orientation.

03:55 We have a left, we have a right, and we have a posterior or non-coronary leaflet.

04:02 And that term reflects the fact that there are coronary arteries coming off of these other leaflets.

04:09 So there's a hole just above the aortic valve here called the left coronary ostium.

04:15 Ostium is just our word for hole.

04:17 And that's going to feed into some coronary arteries, just like there's a hole on the right, called the right coronary ostium.

04:24 That's going to feed into the right sided coronary artery system.