There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.
Abstract
The bicuspid (mitral) valve complex of the human heart consists of functional units
which include the valve leaflets, chordae tendineae and the papillary muscles. The
mechanical properties of these functional units depend to a large extent on the link
between the muscle and the valve. This link is usually arranged in a branching network
of avascular tendinous chordae composed of collagen and elastic fibres, which transmit
contractions of the papillary muscle to the valve leaflets. In order to perform their
function efficiently, the chordae have to possess a high degree of elasticity, as
well as considerable strength and endurance. Human chordae tendineae originating from
the left ventricles were obtained from 7 embalmed cadavers and 6 postmortem subjects
of various ages. Samples washed in saline were fixed or postfixed in 9 % formol saline.
Observations were made by illuminating the chordae along their axes. The reflected
images originating from the superficial collagenous layers of the relaxed chordae
showed a striped pattern 11 microm in width. Scanning electron and light microscopy
of the chordae confirmed an undulating pattern of collagen fibrils arranged in bundles
of planar waves in register and around the entire circumference of the chorda. The
dimensions of the waves correlated with those of the striped reflected pattern. The
observed undulating arrangement of the collagen fibrils appears to produce an inherent
built-in elasticity which is likely to be of considerable advantage for a tissue which
is under continuous repetitive stress. The chordae were covered by endocardium composed
of a superficial layer of smooth squamous endothelial cells and an underlying dense
layer of elastic fibres. It is suggested that the relaxed striped chordae, consisting
of undulating collagen fibrils, straighten when the chordae become stretched by papillary
muscle contraction, thereby mitigating the peak stress developed during muscle contraction.
On relaxation the elastic tissue tends to return the collagen to its wavy configuration.
It is also suggested that the regular wavy pattern of collagen seen in young individuals
gradually changes with age by elongation of the wave pattern which eventually becomes
randomised. In addition, with increasing age, substantial cushions of connective tissue
appear below endocardium while the dense collagenous core has a reduced cross-sectional
area which may lead to stretching and eventual rupture of the chordae.