The conus valves of the adult gilthead seabream (Sparus auratus)

Abstract

The conus (bulbo-ventricular) valves of teleosts perform a key function in the control of blood backflow during ventricular diastole. However, the structural characteristics of these valves are almost unknown. This paper presents a systematic anatomical, histological and structural study of the conus valves of the adult gilthead seabream (Sparus auratus). S. auratus shows two major left and right valves consisting of the leaflet and the supporting sinus. Each valvar leaflet can be divided into a stout proximal body and a flap-like distal region. The proximal body is structured into three layers: a luminal fibrosa, a dense cellular core and a parietal fibrosa. The luminal fibrosa is a collagenous structure extending the entire length of the leaflet, while the parietal fibrosa is restricted to the most proximal area. The dense cellular core consists of fibroblastic cells and a matrix rich in glycoconjugates, collagen and elastin.The histochemical and structural data suggest that the luminal fibrosa bears most of the force associated with valvar closure, while the cellular core acts as a cushion dampening vibrations and absorbing the elastic recoil. The sinus wall is a fibrous layer which shows proximal-distal differences in thickness. It also shows compositional differences that can be related to mechanical function. We describe the presence of a fibrous cylinder formed by the sinus wall, the fibrous interleaflet triangles and the fibrous layer that covers the inner surface of the conus myocardium. This fibrous cylinder constitutes the structural nexus between the ventricle, the conus and the bulbus arteriosus, provides support for the conus valves and separates the valvar complex from the surrounding tissues. The structure of the conus valves in S. auratus is different from that found in other vertebrates. Anatomical similarities between the conus valves and the mammalian arterial valves are emphasized. Each phyletic group appears to have developed specific structures in order to perform similar functions.

Conus arteriosus of the teleost heart: Dismissed, but not missed

“…2c-e) that should facilitate valve movement. This appears to be a common pattern for the teleost OFT valves and coincides with previous descriptions (Icardo et al, 2003). However, there are several exceptions.…”

“…2h). The presence of a fibrous ring establishing the continuity between the ventricle, the conus, and the bulbus was described in an earlier study (Icardo et al, 2003). Its existence as a general feature is confirmed here.…”

“…2c and d and 3e-g) and elastin (Fig. 1b) (see also Icardo et al, 2003). The flap-like part of the valve is composed of a luminal fibrosa and the endocardial covering.…”

“…This segment, a distinct conus arteriosus, is formed by compact myocardium supplied by a coronary vascular tree. The conus myocardium is organized very differently from the completely trabeculated ventricle (Schib et al, 2002) and shows well-developed basement membranes (Schib et al, 2002) and different lectin-binding properties (Icardo et al, 2003).…”

“…Each row consists of left and right valves, although numerous exceptions have been reported (Parsons, 1930;Icardo et al, 2003). Each valve consists of the valve leaflet and the corresponding sinus.…”