Biomedical Engineering Reference
In-Depth Information
Fig. 12.3
A schematic of human heart valves in their anatomical position.
Left
: when the heart
relaxes, the
aortic
and
pulmonary
valves are closed while the
mitral
and
tricuspid
are open.
Right
:
when the ventricles contract: the opposite is true
valves open, and (right) the two valves which regulate the blood flow toward outside
the ventricles closed. The opposite is true in systole (Fig.
12.3
[Right]) when the
ventricles contract.
The two atrioventricular valves, the mitral and the tricuspid, are larger in cross-
sectional area and consist of a number of
cusps, chordae tendinae
and
papillary
muscles
. The cusps (three in the tricuspid and two main ones in the mitral valve)
emanate from a mainly collagenous
annulus fibrosus
and are thin membranes con-
sisting of collagen and elastin fibers embedded in a mucopolysaccharide matrix. The
cusps move for opening or closing the valves on the action of the papillary muscles
via the chordae tendinae.
The arterial or semilunar valves are quite different from the atrioventricular ones.
They are totally passive (no direct muscle contraction involved) and the cups move
to open or close the valves driven only by the pressure difference between the ven-
tricles and the aorta or the pulmonary artery, respectively. The three cusps in each
valve are also thin membranous structures consisting of collagen and elastin fibers
embedded in a mucopolysaccharides matrix.
All vascular cusps are covered with endothelial cells, whose main role is to keep
the flowing blood in its natural state, i.e., to prevent the underlying fibrous structures
from interfering with thrombus formation mechanisms. Apart from the endothelial
cells, few cells exist in the bulk of the cusps material, namely a few fibroblasts.
12.2.1
The Aortic Valve
Let us take the aortic valve as an example for further consideration. This partic-
ular valve consists of three anatomical entities, which function complimentarily.
