Three Layers of the Mitral Valve Leaflet

Three layers of the mitral valve leaflet

Three layers of the mitral valve leaflet are [1]:

1. Atrialis on the atrial side
2. Spongiosa in the middle
3. Fibrosa/ventricularis on the ventricular side.

A dense layer of elastic fibers providing elasticity to the leaflet constitute the atrialis layer. It is covered by endothelium and contains subendothelial connective tissue. Atrialis layer sustains high frequency large tensile deformations in systole.

Spongiosa layer has fine interweaving spongy elastin network rich in glycosaminoglycans and proteoglycans. It resists the compression between the layers (aided by retention of water in this layer), dampens the vibrations of the valve during the high pressure closing motion and gives flexibility to the valve.

Thickest layer is the ventricular aspect constituting the fibrosa layer which is made up of mostly organized collagen fibers giving tensile strength to the valve. It is connected to the mitral annulus and faces the high pressure in the left ventricle.

Reference

1. Robert A. Levine, Albert A. Hagége, Daniel P. Judge, Muralidhar Padala, Jacob P. Dal-Bianco, Elena Aikawa, Jonathan Beaudoin, Joyce Bischoff, Nabila Bouatia-Naji, Patrick Bruneval, Jonathan T. Butcher, Alain Carpentier, Miguel Chaput, Adrian H. Chester, Catherine Clusel, Francesca N. Delling, Harry C. Dietz, Christian Dina, Ronen Durst, Leticia Fernandez-Friera, Mark D. Handschumacher, Morten O. Jensen, Xavier P. Jeunemaitre, Hervé Le Marec, Thierry Le Tourneau, Roger R. Markwald, Jean Mérot, Emmanuel Messas, David P. Milan, Tui Neri, Russell A. Norris, David Peal, Maelle Perrocheau, Vincent Probst, Michael Pucéat, Nadia Rosenthal, Jorge Solis, Jean-Jacques Schott, Ehud Schwammenthal, Susan A. Slaugenhaupt, Jae-Kwan Song, and Magdi H. Yacoub, for the Leducq Mitral Transatlantic Network. Mitral Valve Disease–Morphology and Mechanisms. Nat Rev Cardiol. 2015 Dec;12(12):689-710.