The three‐dimensional arrangement of the myocytes in the ventricular walls

Abstract

The arrangement of the myocytes aggregated together within the ventricular walls has been the subject of anatomic investigation for more than four centuries. The dangers of analyzing the myocardium on the basis of arrangement of the skeletal myocytes have long been appreciated, yet some still described the ventricular myocardium in terms of a unique band extending from the pulmonary trunk to the aorta. Another current interpretation, with much support, is that the ventricular myocytes are compartmentalized in the form of sheets, albeit that the extent of division, and interrelations, of the sheets is less well explained. Histological examination, however, shows that the only muscular unit to be found within the myocardial walls is the cardiac myocyte itself. Our own investigations show that, rather than forming a continuous band, or being arranged as sheets, the myocytes are aggregated together as a three-dimensional mesh within a supporting matrix of fibrous tissue. Within the mesh of aggregated myocytes, it is then possible to recognize two populations, depending on the orientations of their long axes. The first population is aligned with the long axis of the aggregated myocytes tangential to the epicardial and endocardial borders, albeit with marked variation in the angulation relative to the ventricular equator. Correlation with measurements taken using force probes shows that these myocytes produce the major unloading of the blood during ventricular systole. The second population is aligned at angles of up to 40 degrees from the epicardium toward the endocardium. The correlation with measurements from force probes reveals that these intruding myocytes produce auxotonic forces during the cardiac cycle. The three-dimensional arrangement of the mesh also serves to account for the realignment of the myocytes that must take place during ventricular contraction so as to account for the extent of systolic mural thickening.

Determinants of left ventricular shear strain

“…It is this distribution of ␣ t that was used in the FIB simulation. Meanwhile, more recent experimental investigations have confirmed the earlier observations by Streeter and colleagues that myofiber orientation in the LV wall has a component in transmural direction (1,13,18,23,24,25,32). Accurate quantification of ␣ t has proven to be difficult, among others, because the unique definition of a wall-bound coordinate system to which the fiber orientation can be referred to is difficult (13).…”

The length-force behavior and operating length range of squid muscle varies as a function of position in the mantle wall

“…Thompson et al (Thompson et al, 2010a) showed in D. pealeii that the inner surface of the mantle experiences 1.3 to 1.6 times greater circumferential strain than the outer surface at any time point during the exhalant phase of a jet. Because circular fibers are oriented in transverse planes of the mantle and also appear to follow a perfectly circumferential trajectory, there are no architectural specializations, such as those found in mammalian cardiac ventricle muscle (Lunkenheimer et al, 2004;Anderson et al, 2006;Anderson et al, 2009) or vertebrate skeletal muscles (Alexander, 1969;Rome and Sosnicki, 1991;Wakeling and Johnston, 1999;Azizi et al, 2008) that could permit all of the fibers to experience approximately the same range of strains during jetting. Thus, the transmural gradient of circumferential strain in the mantle may require muscle fibers from the inner surface to operate farther left on the ascending limb of the length-tension curve at any instant during mantle contraction.…”

Engineered Contractile Skeletal Muscle Tissue on a Microgrooved Methacrylated Gelatin Substrate

“…2 Ideally, engineered tissues should have the same characteristics as the tissues that they were designed to mimic. For many tissues such as the myocardium, 3 smooth muscle, 4 and skeletal muscle, 5 the tissue function is closely linked to the cell organization and alignment. Therefore, controlling the structure and properties of the tissues by changing the extracellular matrix composition and substrate topography is crucial for proper cell alignment, organization, and differentiation.…”