Synovial membrane asks for independence

Synovial membrane is traditionally considered as a part of the joint capsule. It, however, differs from fibrous part of the capsule in development, structure, function, vascularisation, innervation and involvement in pathological processes. Moreover, in some areas, it even does not contact with the fibrous capsule. Thus, it appears that the synovial membrane should be considered as an independent organ and not as the lining of the joint capsule.

Formation of synovial joints and articular cartilage

Chondrocytes differentiate from mesenchymal progenitors and produce templates(anlagen) for the developing bones. Chondrocyte differentiation is controlled bySox transcription factors. Templates for the neighbour bones are subsequentlyseparated by conversion of differentiated chondrocytes into non-chondrogeniccells and emergence of interzone in which joints cavitation occurs. A central rolein initiating synovial joint formation plays Wnt-14/beta-catenin signalling pathway.Moreover, bone morphogenetic proteins and growth and differentiation factorsare expressed at the site of joint formation. Joint cavitation is associated withincreased hyaluronic acid synthesis. Hyaluronic acid facilitates tissue separationand creation of a functional joint cavity. According to the traditional view articularcartilage represents part of cartilage anlage that is not replaced by bone throughendochondral ossification. Recent studies indicate, however, that peri-joint mesenchymalcells take part in interzone formation and that these interzone cellssubsequently differentiate into articular chondrocytes and synovial cells. Thus,anlage chondrocytes have a transient character and disappear after cessation ofgrowth plate function while articular chondrocytes have stable and permanentphenotype and function throughout life

Comparative and Developmental Anatomy of Cardiac Lymphatics

The role of the cardiac lymphatic system has been recently appreciated since lymphatic disturbances take part in various heart pathologies. This review presents the current knowledge about normal anatomy and structure of lymphatics and their prenatal development for a better understanding of the proper functioning of this system in relation to coronary circulation. Lymphatics of the heart consist of terminal capillaries of various diameters, capillary plexuses that drain continuously subendocardial, myocardial, and subepicardial areas, and draining (collecting) vessels that lead the lymph out of the heart. There are interspecies differences in the distribution of lymphatic capillaries, especially near the valves, as well as differences in the routes and number of draining vessels. In some species, subendocardial areas contain fewer lymphatic capillaries as compared to subepicardial parts of the heart. In all species there is at least one collector vessel draining lymph from the subepicardial plexuses and running along the anterior interventricular septum under the left auricle and further along the pulmonary trunk outside the heart and terminating in the right venous angle. The second collector assumes a different route in various species. In most mammalian species the collectors run along major branches of coronary arteries, have valves and a discontinuous layer of smooth muscle cells

Ultrastructural analysis of capsule and nurse-cell morphology examined seven months after Trichinella spiralis mouse infection.

Ultrastructural changes in muscles cells of mice infected with T. spiralis larvae in 220 day of infection were evaluated. The object of study was in the region of the „nurse-cell” being in direct contact with the larva wall. Electron microscopic observations revealed the continuity of the muscle cell membrane adjacent to larva surface