These two latter functions of the ECM are considered to be mechanobiological as opposed to merely biomechanical since they affect cell behavior. Third, the various types of ECM have different innate mechanical behaviors, for example with collagen being stiffer than elastic fibers, and a growing body of research has demonstrated that the phenotype and function of cells, including valve cells, are influenced by the stiffness of the substrate to which they are adhered. The PCM influences cell function by serving as a source of ligands for cell surface receptors, which transfers mechanical strains (experienced by the leaflet tissues) to the cells and initiates intracellular signaling pathways. Second, the valvular cells are bound to and surrounded by the ECM that is located within the immediate vicinity of the cell this ECM is specifically known as the pericellular matrix (PCM). First, the ECM plays a biomechanical role: it is responsible for the unique mechanical behavior of the valve tissue and thus the overall valve function. Taken together, the ECM performs several roles in heart valves. The ECM within heart valves is primarily comprised of collagen, elastic fibers, and proteoglycans and glycosaminoglycans, although other ECM components are present as well. The ability of heart valves to open and close repeatedly, as well as the maintenance of the phenotypes of valvular cells, is made possible by their tissue microstructure, specifically the composition and orientation of extracellular matrix (ECM). The opening and closing of valve leaflets at precise times during the cardiac cycles contributes to the generation of sufficiently high pressure to eject blood from the ventricles, and also prevents blood from flowing backwards into the heart instead of forward towards the systemic circulation and the lungs.
The normal function of the heart valves is essential to cardiovascular and cardiopulmonary physiology. There are four valves in the heart, located at the entrance to and exit from the ventricular chambers. Heart valves are thin, complex, layered connective tissues that direct blood flow in one direction through the heart.
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