Heart Wall - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 305

wide collagen bundles. These circumferential bundles are arranged in a corrugated
manner for radial expansion. A matrix with elastin surrounds the collagen bundles.
The ventricularis contains collagen and elastin fibers, which are less organized
than in the fibrosa. However, elastin sheets provide recoil, which retains the folded
shape of the fibrosa. The loosely organized spongiosa, between the fibrosa and
ventricularis, contains glycosaminoglycans, collagen, and elastin mostly in the
radial direction. The spongiosa could act as load buffer for the fibrosa and the
ventricularis.
The heart structure provides the 3 properties of contractility, automatism, and
conduction due to 2 types of cardiac muscular cells: myocardial and nodal myocytes.

6.2.4.1 Mathematical Histology

Structure-function features of the heart have been mathematically investigated.
Two fiber networks have been particularly studied: (1) the network of collagen
fibers of the aortic valve cusp, and (2) the myofibers of the left ventricle wall, using
a simple model of mechanically loaded fibers. The structure of the aortic leaflet
has been derived from its function, which is assumed to consist of supporting a
uniform pressure load undergone by a single family of fibers under tension [ 588 ].
The equation of equilibrium for the fiber structure is solved to determine its
architecture. The computed fiber architecture resembles the real one. Assuming
a constant myofiber cross-sectional area, symmetry with respect to the ventricle
axis, small wall thickness with respect to the other dimensions, and a stress tensor
resulting from hydrostatic pressure and myofiber stress, the bundles of myofibers
have been shown to be located on approximate geodesics on a nested set of toroidal
surfaces centered on a degenerate torus in the equatorial plane of the cylindrical part
of the left ventricle [ 589 ].

6.2.5 Conduction Paths of the Depolarization Wave

The sinoatrial node act as the primary cardiac pacemaker. Together with nodal
cells in the atrioventricular node (secondary cardiac pacemaker) and those of
the ventricular nodal circuit, they constitute the cardiac conduction network of
electrochemical waves (or action potentials).

6.2.5.1 Nodal Cells

×

Nodal cells are small (80-100 m), specialized cardiomyocytes with few

myofibrils that create or quickly spread depolarization waves in the myocardium.
The conducting cells are wider than actual cardiomyocytes. They are not branched.

10-20