A study on the fine structure of Clonorchis sinensis, a liver fluke II. The alimentary tract and the excretory system

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Abstract
A morphological study on the ultrastructures of the alimentary tract and the excretory system of Clonorchis sinensis was conducted. The liver flukes were collected from rabbit liver six months after the experimental infection The worms were washed with 0.85% saline solution and immediately moved to cold 2.5% glutaraldehyde in 0.1 M phosphate buffer pH 7.4. The materials were dissected and fixed for two hours. The blocks were post-fixed in 1% osmium tetroxide. The blocks were embedded in Epon 812. Ultra thin sections were cut with Sovall MT-2 ultramicrotome and stained with uranyl acetate and lead citrate. Sections were then observed with Hitachi HS-7S electron microscope. The following results were obtained in a series of observations. The walls of oral cavity and esophagus comprised tegumental syncytium, basement membrane, loose connective tissue, muscular layer and parenchymal cells. The apical surface and the base of the syncytium were covered with a protoplasmic membrane for each forming numerous invaginations. Granular endoplasmic reticulum was developed in the epithelium of the oesophagus. The gastrodermis of Clonorchis sinensis comprised two types of cells in general. The first cell type was numerous one forming a single continuous layer of epithelial cells. Each of the cells had outfolded cytoplasm into the caecal lumen and lamellae along the cell surface. Among the above epithelial cells, no considerable differences in structure reflecting their functional states were identified. The second cell type was less differentiated in nature and lay within the gastrodermis above the basement membrane but not in contact with the caecal lumen, being overlapped by neighboring gastrodermal cells of the type described above. At this portion the gastrodermis seemed to be a pseudostratified epithelium. There were well-developed lamellae along the surface of epithelia of all canals or duct concerning evacuation. The excretory pore was 7.5 micrometer in diameter and dorso-terminally opended. The epithelium of the excretory pore, a syncytial layer, contained many microtubules unlike the other part of tegumental layer of this worm. The epithelium thickness of the excretory pore was very irregular(1.3-5.5 micrometer).