ELECTRON MICROSCOPIC STUDY OF THE INTESTINAL EPITHELIUM
OF SACCOGLOSSUS MERESCHKOWSKII (ENTEROPNEUSTA, HEMICHORDATA)
M. V. Stolyarova
St. Petersburg State Pediatric Medical Academy, Department of Histology and Embryology;
e-mail: mvstolyarova@yandex.ru
Epithelium of the hepatic region of the intestine in Saccoglossus mereschkowskii, a representative of enteropneusts
(Enteropneusta, Hemichordata) standing at the base of Chordata, has been investigated using electron
microscope. The ultrastructure of ciliated and granular epithelial cells, elements of the intraepithelial nerve layer,
and intercellular junctions have been characterized. The data concerning details of the organization of the ciliary
apparatus and rootlets system are presented. It is justified the presence of complicated supporting construction
of cilia which performs a mechanical stabilizing function and possibly also provide synchronization of ciliary
movements. The presence of cilia with two centrioles is considered as an adaptation to high functional load
on ciliary apparatus. Well developed bundles of myofilaments are found in the cytoplasm of the basal portions
of ciliary cells that characterizes these cells as myoepithelial. The features indicating the role of ciliary cells in
absorption are described. The capability of these cells to balloon-like secretion is considered. Data on the accumulation
of food reserves in the form of lipid droplets and glycogen in the cell cytoplasm are presented. Ciliated
cells are characterized by their function as ciliated secretory-absorptive myoepithelial cells. Based on the location
of secretory granules both in the apical and basal portions of granular cells, an exocrine-endocrĝine function
of these cells has been suggested. Typical endocrine cells in the intestinal epithelium of S. mereschkowskii are
absent. Several types of granules in the nerve fibers cytoplasm are described. Junctions between the nerve fibers
and basal portions of ciliary and granular epithelial cells are found. Nerve regulation of contractile and secretory
functions of epithelial cells is supposed. The presence of the regulatory nerve-endocrine system that includes receptor
cells of open type, secretory endocrine-like cells and nerve elements of nerve layer is supposed in the intestinal
epithelium of enteropneusts.
Key words: comparative histology and cytology, invertebrates, epithelium
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