Anatomy and histology of the cardiac conal valves of the adult dogfish (Scyliorhinus canicula).

BACKGROUND

Knowledge of the structural arrangement of the cardiac conal valves in Elasmobranchs is scarce. The present study was designed to assess the anatomical and histological features of the conal valves of the dogfish as a starting point for further investigation of the mechanical properties of these valves.

METHODS

The sample examined consisted 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-ventral aorta junction and is composed of three valves of similar size. The posterior row is near the conus-ventricular junction and consists of four valves, one of them very reduced in size. Each valve shows two components, namely, the leaflet and its supporting structure, the sinus. In the anterior valves, the length of the leaflets between their lateral attachments to the sinus wall is remarkably longer than the straight-line distance between the points of attachment. This allows each leaflet to close against the other two leaflets of the same row, even when the conus is relaxed. The leaflets of the posterior valves are anchored to the conus wall by means of tendinous cords and cannot practically bridge the lumen of the relaxed conus. Each leaflet has a stout central body in which the connective tissue is stratified in three layers: outer fibrosa, spongiosa, and inner fibrosa. The lateral parts of the leaflet mainly consist of a single fibrous layer that bifurcates into the outer and inner fibrosa layers of the central body. The sinus walls of the posterior valves are entirely made up of conal tissue, whereas those of the anterior valves incorporate an aortic component.

CONCLUSIONS

The present findings suggest that the inner fibrosa and the fibrous lateral portions of the leaflets mainly bear the stress of pressure generated by blood backflow. The stretching of the leaflets in the radial direction may basically depend on the spongiosa, whereas the outer fibrosa determines the radial stiffness of the leaflets.