V. Sanscoma et al., ANATOMY AND HISTOLOGY OF THE CARDIAC CONAL VALVES OF THE ADULT DOGFISH (SCYLIORHINUS-CANICULA), The Anatomical record, 241(4), 1995, pp. 496-504
Background: Knowledge of the structural arrangement of the cardiac con
al valves in Elasmobranchs is scarce, The present study was designed t
o assess the anatomical and histological features of the conal valves
of the dogfish as a starting point for further investigation of the me
chanical properties of these valves. Methods: The sample examined cons
isted of 31 adult dogfishes, The study was carried out using scanning
electron microscopy and histological techniques for light microscopy.
Results: In the dogfish, the conus arteriosus contains two transverse
rows of valves. The anterior row lies at the level of the conus-ventra
l aorta junction and is composed of three valves of similar size. The
posterior row is near the conus-ventricular junction and consists of f
our valves, one of them very reduced in size, Each valve shows two com
ponents, namely, the leaflet and its supporting structure, the sinus.
In the anterior valves, the length of the leaflets between their later
al attachments to the sinus wall is remarkably longer than the straigh
t-line distance between the points of attachment. This allows each lea
flet to close against the other two leaflets of the same row, even whe
n the conus is relaxed. The leaflets of the posterior valves are ancho
red to the conus wall by means of tendinous cords and cannot practical
ly bridge the lumen of the relaxed conus. Each leaflet has a stout cen
tral body in which the connective tissue is stratified in three layers
: outer fibrosa, spongiosa, and inner fibrosa. The lateral parts of th
e leaflet mainly consist of a single fibrous layer that bifurcates int
o the outer and inner fibrosa layers of the central body. The sinus wa
lls of the posterior valves are entirely made up of conal tissue, wher
eas those of the anterior valves incorporate an aortic component. Conc
lusions: The present findings suggest that the inner fibrosa and the f
ibrous lateral portions of the leaflets mainly bear the stress of pres
sure generated by blood backflow. The stretching of the leaflets in th
e radial direction may basically depend on the spongiosa, whereas the
outer fibrosa determines the radial stiffness of the leaflets. (C) 199
5 Wiley-Liss, Inc.