Ultrastructural and Histochemical Study on the Epithelia of Digestive Tract of a Korean Slug, Incilaria fruhstorferi

Jung Chan Lee, Nam Sub Chang and Jong Min Han
Department of Biology, Mokwon University. Taejon 301-729, Korea
We report the results on the observations of each anatomical region in gastrointestinal tract of Incilaria fruhstorferi, Korean slug, in ultrastructural and histochemical considerations of cell populations and distribution of gastrointestinal tract epithelium and secreting granules.   Gastrointestinal tract of Incilaria fruhstorferi is composed of esophagus, stomach, intestine and rectum. Esophagus is divided into proesophagus, crop and postesophagus, and intestine is composed of prointestine, midintestine and postintestine.   According to the result of observations on each anatomical region in gastrointestinal tract, following ten populations of cell are documented.  1) three kinds of green granular cell,  2) blue granular cell,  3) mucous cell, 4) two kinds of ciliated columnar epithelial cell,  5) clear cell,  6) reticular-shaped cell, and 7) degenerated cell.   Two kinds of ciliated columnar epithelial cell are divided into type A and B. Type A cell has both cilia and microvilli on its upper free surface, but type B cell was dark because of its high electron density and was characterized as to be only found in intestine and rectum. The cilium showed typical 9 x 2 + 2 axoneme structure.   Three kinds of green granular cell are divided into type A, B and C, and those were characterized as to be mainly found in the crop, postesophagus, stomach and rectum. Both type A and B cells contained fat droplets (1.36 x 1.67 ㎛ in diameter), which are positively stained with Sudan black B, but type C cell had glycogen, additionally.   Blue granular cell was tallest among above mentioned ten kinds of cells and contained rounded granules, which were confirmed as a protein material by Millon reaction. These were only found in midintestine.  Mucous cell that was mainly found in both of intestine and rectum contained two kinds of granules. One is electron lucent granule and the other is dark electron dense granule (1.33 x 0.89 ㎛ in diameter), but lucent granule(2.66 ㎛ in diameter) was observed only at immature stage. Each lucent and dark granules is confirmed as an acid and neutral mucin granule exhibiting positivity on alcian blue (pH 2.5) and PAS stain, respectively. Both type A and type B clear cells were observed by light microscope, and type A cell was confirmed as a neuroendocrine cell by electron microscopy, while the nature of type B cell was confirmed as a fat storage cell. The size of granule in neuroendocrine cell was about 0.16 ㎛.   Reticular-shaped cell was small and having irregular contour. The cell was mainly found in stomach, and had large nucleus. Mitochondria and granular vesicles were found in small amount of cytoplasmic process.   Degenerated cells were mainly found in postintestine and rectum, and were confirmed as to be formed during breaking process after granules were secreted.
  
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