Valves of the Heart

00:01 Okay.

00:02 We've talked about myocardium.

00:03 Let's talk about valves.

00:06 So again, looking at the top of the heart at the base of the heart down onto the heart, we're seeing, in the starting in the upper left hand corner, the tricuspid valve, down to the pulmonic valve, which is in the anterior wall at the bottom.

00:21 And then we go out to the lungs and back through the mitral valve, the upper right hand corner, and then finally the left ventricle pumps out through the aortic valve.

00:29 So let's get some nomenclature straight here.

00:33 When we talk about the semi lunar valves, they're called semi lunar valves, the aortic and pulmonic valve are called semi lunar, because each cusp kind of looks like a half moon.

00:44 Somebody was on drugs when they thought about that, but anyways, that's why it's called semi lunar.

00:50 And the valve component of the semi lunar valves, the aortic and mitral valve are called cusps.

00:57 On the other hand, if you're talking about the atrioventricular valves, the valve structure is called a leaflet.

01:04 Alright? So cusps and leaflets.

01:08 Same general organization, they just have different names.

01:11 Okay.

01:12 We're looking at a semi lunar valve that is open and is closed.

01:17 The semi lunar valves open and close on their own, they don't need anything other than pressure differential between the top and the bottom of the valve.

01:27 On the other hand, the tricuspid and the mitral valve need to have an intact annulus and valve and chordae tendineae and all that other stuff.

01:37 Again, you can just see the way that the mitral valve looks when it's open versus when it's closed.

01:42 And the kind of irregular tooth like thing at the top of that open valve, just is reflecting the edge of the valve going into the chordae tendineae.

01:51 And similarly, in the tricuspid valve, even though it's got three leaflets.

01:57 And it's called a tricuspid valve, go figure.

02:01 Three leaflets, it's also going to have the same general appearance when it's open versus closed.

02:06 What does this look like histologically? And again, this is for the cognoscenti.

02:10 I don't think it's ever appeared once on boards, but I find the structure incredibly interesting.

02:16 It is not just fibrous connective tissue, there is an outflow surface on every valve that is dense collagenous material, it's type 1, type 3 collagen, it's called the fibrosa.

02:27 On the inflow surface of every valves and elastin rich layer, and this is depending whether you're facing the ventricle, or the atrium, it's called the ventricularis or the atrialis.

02:37 That top layer, the fibrosa, very stiff, and gives strength and integrity to the valve.

02:44 That bottom layer, very, very flexible, because it's got a lot of elastic tissue in it, and allows the valve to rapidly close when pressure changes occur.

02:53 Well, that bottom is flexible, that top is stiff, we need a layer in between to kind of mitigate between the two expansion moduli.

03:03 That's loose connective tissue, and that's called the spongiosa.

03:07 The various layers, spontaneously formed, there are various cells in here, they're constantly turning over and making the matrix that's different in each of those three layers and those cells can independently form each of the three layers.

03:24 On either side of the valve, again, this is valve in contact with liquid blood.

03:28 There's endothelium, very hard to see on this slide, but there's endothelium lining both.

03:32 Okay.

03:33 You now know more about valve architecture than 99.99% of the human population. Congratulations.

03:43 Okay, more about valves.

03:44 So we have the tricuspid and the mitral valve indicated here, we have the aortic valve.

03:48 And again, this is making the point about the integrity of the valves depending on different kinds of structures.