Deviation of the Tunica Media of Aorta of Goat from Conventional Structural Concept : case for including Collagen

Abstract

Knowledge of the structural organization of the aortic tunica media is important in understanding the physicomechanical properties and alterations which underpin aor tic aging and pathologies such as atherosclerosis, aneurysms and aortitis. Recent studies have cast doubt on the exclusivity of the medial lamella unit and musculoelastic fascicle concepts of the aortic structure. The goat is a suitable model for studying cardiovascular disease. Therefore the structure of tunica media of its aorta was studied by transmission electron microscopy. Materials were obtained from 6 healthy adult male goats [age range 12–24 months]. Specimens from the mid thoracic aortic segment were fixed in 3% phosphate buffered glutaraldehyde and processed for durcupan embedding and sectioning. Ultrathin sections were stained with uranyl acetate, counterstained in lead citrate and examined by Philips 210 transmission electron microscope. Besides medial lamella units and musculoelastic fascicles in the tunica media, we observed longitudinal elastic lamellae, and cells surrounded by collagen bundles both of which were sandwiched by elastic lamellae. In some instances, cells were disposed between collagen bundles on one side, and elastic lamella on the other. These observations imply that the aortic tunica media is heterogeneous with a mosaic structure, rather than the uniform one conventionally known.