papillary muscle physiology question

[blaze626]

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The leaflets of the av valve are attached to chordeae tendineae that are attached to papillary muscles that are attached to the wall of the ventricle. Therefore, they must be loose inside the ventricle when the av valve is open. When the av valve closes, it is kept from swinging into the atrium by the chordeae tendineae. So, are the papillary muscles there to pull the av valve open after ventricular contraction? Why doesnt the av valve just open passively at this point? And if it does, what would be the point of the papillary muscles?

 

[BlackNDecker]

If you recall from anatomy, during dissection of the heart, the conduction system is intimately associated with the papillary muscle of the right ventricle via the moderator band.

While the function of this conductive tract has not been completely elucidated, depolarization of the moderator band would slightly precede RV contraction and (via papillary muscle shortening) prevent atrioventricular valve prolapse.

So, are the papillary muscles there to pull the av valve open after ventricular contraction?

No. As noted above, the papillary muscles function to prevent atrioventricular valve prolapse. Clinically, you can appreciate this with papillary muscle dysfuntion or rupture following an MI (most commonly the anterolateral papillary muscle is affected due to its singular blood supply). You will find that the predominant finding is regurgitant blood flow during systole...(rather than stenosis which would be expected if the role of the papillary muscle was to "pull" the valve open).

Why doesnt the av valve just open passively at this point? And if it does, what would be the point of the papillary muscles?

They do open passively...during early diastolic filling. Go back and study the RV pressure diagram and JVP waveforms.

Think of the chordae and papillary muscles as thethering cords rather than contractile elements and you will be fine...