ULTRASTRUCTURAL ASPECTS OF RAT TAIL TENDON SHEATHS

  • 1 January 1985
    • journal article
    • research article
    • Vol. 140  (JAN) , 57-67
Abstract
The sheaths which envelop rat tail tendons were studied. The samples were processed for observation by light microscopy and EM. In the case of EM, thin sections of specimens embedded in epoxy resin and replicas of freeze etched samples were used. On the basis of histological and ultrastructural observations, 4 distinct connective tissue sheaths were detected. The paratendineum is thick fibrous sheath that externally covers the 4 groups of tendons arranged around the vertebrae of the tail; the epitendineum is a distinct fibrous sheath surrounding each tendon group; the peritendineum is composed of concentric celluar laminae enveloping each tendon; and the endotendineum is made up of 1 cellular lamella which adheres to the fibers of the tendon, projecting trabeculae between the individual tendn fascicles. In the para- and epitendineum, thick bundles of collagen fibrils, running parallel to the fibers of the tendon, were visible. The collagen fibrils had a wide variability of diameters (from 35-220 nm) and, when examined in replica, their microfibrillar arrangement appeared to be straight. In the peri- and endotendineum, thin bundles of collagen fibrils were visible between the cellular laminae, parallel to the main axis of the tendon. Among these collagen bundles, elastic fibers and numerous glycoproteins containing microfibril-like filaments were visible. The collagen fibrils were small and of uniform diameter (50 nm) and, when observed in replica, showed a helicoidal microfibrillar arrangement. The cell layers of the peri- and endotendineum were made up of flattened fibroblasts which were connected by specialized junctions and which contained numerous micropinocytotic vesicles. A thin layer of granular electron-dense material, with ultrastructural characteristics similar to those of a basal lamina, was visible on the surface of the most external cellular layer of the peritendineum and on the outer surface of the cellular lamella of the endotendineum. Due to their morphological characteristics it the 4 tendon sheaths seemingly are involved in different and special functions. Collagen Type I and collagen Type III, respectively show a close similarity in distribution to the thick collagen fibrils, with a straight microfibrillar arrangement, of the 2 external sheaths and to the thin collagen fibrils, with a helicoidal microfibrillar arrangement, of the 2 internal sheaths.