ultrastructural study of the atrioventricular valves in the mice

ABSTRACT

Mice atrioventricular valves exhibit a number of morphological similarities to their human homologues. This research aimed to undertake a thorough study of the atrioventricular valves of mice. The success of treatment of the atrioventricular valve diseases is dependent on a thorough knowledge of its anatomy. In the present study, 20 mice of both sexes were used. The thoracic walls of the animals were opened, and the hearts were extracted and washed thoroughly with phosphate buffered saline. The annulus, leaflet tissue, chordae tendineae, and papillary muscles of the tricuspid and mitral valves were carefully dissected. The dissected specimens were processed for light and transmission electron microscopic examinations. The fine structure proved to be the same in both atrioventricular valves. The leaflets of the two AV valves were formed of a fibrous layer in its lower third [on the ventricular side] and a spongy layer in its middle third [on the atrial side] where the muscle cells were progressively lost. The fibrosa consisted of collagenous bundles that were differently oriented in right and left AV valves. The spongiosa was formed by a loose network of thin collagen fibers, fibroblasts and scattered elastic fibers. The chordae tendineae were structurally similar in the two AV valves where they were formed of three distinct layers an outer layer of simple flattened endocardial cells, a basal lamina of loose collagen and few elastic fibres, and a central core of collagen with few scattered fibroblasts. The papillary muscles of the left ventricle extended from the heart apex toward the annulus fibrosus. In one third of specimens, the anterior papillary muscle has a free base that was always attached to the ventricular wall by thin chordae tendineae. The present study has demonstrated the microanatomy of the AV valves in mice, hoping at enhancement of human clinico- pathologic correlation when their functions become abnormal