花背蟾蜍蝌蚪胃的发育形态学观察

Developmental Morphology of the Stomach in Siberian Toad(Bufo raddei) Tadpoles

应用大体解剖、组织切片和扫描电镜3种形态学方法对花背蟾蜍(Bufo raddei)蝌蚪在生长发育和变态过程中胃的形态结构变化进行了观察。结果显示,在蝌蚪发育24期(即G24)消化道呈简单的管状结构,胃与小肠等区分不明显,胃壁由内层矮柱状黏膜上皮细胞和其外的扁平上皮细胞层构成;直到26期胃略膨大,呈短粗管状,与小肠和食道可明显区分,胃壁内层的黏膜上皮细胞呈高柱状,上皮细胞间出现少量杯状细胞;36期的胃管明显膨大,其壁已具有胃的4层基本组织结构,杯状细胞数量增加,黏膜上皮细胞游离面有细长的微绒毛交织成网状覆盖;42期胃发育呈"C"字形,胃壁具备了消化道典型的4层结构,有胃腺芽出现,黏膜细胞的微绒毛短而直立,仅极少数细胞有长的微绒毛;蝌蚪发育到46期,肠道缩短,胃呈"J"字状,占消化道大部分,胃体中胃腺发达。在临近肝一侧,黏膜上皮细胞的微绒毛较短,胃腺少而小;而在相反一侧,微绒毛较长,胃腺多而大。基于上述结果说明,花背蟾蜍蝌蚪胃在36期已经基本完成了组织结构的分化,在变态发育期间结构和功能得到进一步完善,以适应变态后陆地生活的食性变化。

The morphological changes of stomach during siberain toad（Bufo raddeis） tadpole development were investigated with gross anatomic, general histological and scanning electron microscopic methods. We measured the lengths of tadpole body, digestive tract and stomach, thicknesses of stomach wall, mucosa, submucosa, muscle and serosa, and height of epithelial cells, and analyzed their relationship during development by one-way ANOVA. The developmental stages of siberain toad tadpole were identified according to Gonser′s method. During the tadpole development, the digestive tract elongated from an average length of 15.98 mm at stage 26 to 64.68 mm at stage 36, and then shortened from an average length of 64.68 mm at stage 36, 38.45 mm at stage 42 to 16.12 mm at stage 46（Table 1）. The stomach increased from an average length of 1.83 mm at stage 26, 2.35 mm at stage 36, 3.00 mm at stage 42 to 3.47 mm at stage 46（Table 1）. At stage 24（PlateⅠ： 5）, the digestive tract differentiated into simple tubular structure without a distinguished stomach, the wall of stomach was composed of an inner layer of mucosal epithelial cells and an outer layer of squamous epithelium cells. The thickness of stomach was 6.53 μm in average, of which epithelial cell was 5.38 μm in height and serosa was 1.08 μm in thickness（Table 2）. While at stages 26 to 30（PlateⅠ： 1, 2）, the stomach appeared as a fatter and shorter tube compared to other parts of the digestive tract. The stomach wall kept the two-layer structure and the mucosal epithelial cells became highly columnar in shape and few goblet-like cells appeared among the epithelial cells（PlateⅠ： 6, 7）. The thickness of stomach at stage 26 was 7.61 μm in average, of which epithelial cell was 7.05 μm in height and serosa was 0.75 μm in thickness（Table 2）. The thickness of stomach at stage 30 was 12.01 μm in average, of which epithelial cell was 9.29 μm in height and serosa was 2.72 μm in thickness（Table 2）. At stage 36（PlateⅠ： 2, 9）, the stomach was obviously swollen and its wall developed into the general structures with four-layers of tissue compounds. Goblet cells appeared in a large number. The free surface of mucosal epithelial cells covered with slender microvilli interwoven into a mesh as revealed by SEM observation. The thickness of stomach was 30.95 μm in average, of which epithelial cell was 9.94 μm in height, mucusa was 20.06 μm in thickness（Table 2）; submucusa layer was 5.17 μm in thickness, muscle layer was 3.16 and serosa layer was 2.55 μm in thickness（Table 2）. At stage 42（PlateⅠ： 3, 10）, the stomach became to a C-like shape, typical four-layer structure of the stomach wall formed well and the gastric bud appeared; the microvilli of most mucosal epithelial cells were short and erect, and only few cells covered with long microvilli were found by SEM observation. The thickness of stomach was 20.72 μm in average, of which epithelial cell was 7.62 μm in height, mucusa was 10.47 μm in thickness（Table 2）; submucusa layer was 4.8 μm in thickness, muscle layer was 2.29 and serosa layer was 2.72 μm in thickness（Table 2）. With the development of tadpoles from stage 42 to stage 46（PlateⅠ： 4, 12）, the intestinal tract became shorter and the stomach became larger in a J-like shape and became a major part of the digestive tract. A large number of gastric glands were observed in stomach. At the side adjacent to liver, microvilli of mucosal epithelial cells in the stomach wall adjacent to liver were long, and gastric glands were less and smaller; while at the opposite side, microvilli were short, and gastric glands were more and larger. The thickness of stomach was 70.21 μm in average, of which epithelial cell was 7.73 μm in height, mucusa was 35.17 μm in thickness（Table 2）; submucusa layer was 6.92 μm in thickness, muscle layer was 23.04 and serosa layer was 5.07 μm in thickness（Table 2）. This study indicate that siberain toad tadpole stomach is differentiated foundmentally with four layers in structure at stage 36, and the structure and function were improved to adaptive the land living environment after metamorphosis.