Comparable Study On The Endocrine Function Of The Branchiostoma Belcheri And Styela Plicata Digestive Tract

Histology and immunphistochemistry were used to preliminarily study the morphology and histological structure of digestive tract, endocrine cells in the gastrointestinal tract in Branchiostoma belcheri and Styela plicata. The results were shown as following:The digestive tract of Branchiostoma belcheri is a straight tube, including swallow , esophagus, liver diverticulum, fore-midgu, hind-midgut, hindgut, rectum and anus. The whole tract is composed of single-layered columnar epithelium. The epithelium cells from esophagus to anterior-hind gut arrange densely, karyons of them are comparably big; however, from posterior-hind gut to rectum, the epithelium cells arrange gradually incompactly, and the karyons change smaller. Significant plica are formed in the walls of fore-midguU hind-midgut and anterior-hind gut. From posterior-hind gut to rectum, the plica dissappear gradually.The shape of the Styela plicata digestive tract is "U". The tract includes esophagus, stomach, foreguU midgut, hindgut, rectum and anus. The stomach is divided into cardiac portion , blind sac and pyloric portion according to their morphology and position. From inner to outer, the walls of digestive tract are separated into mucosa, submucosa and serosa. Plicamucosa are formed in the walls of digestive tract. The mucosa epithelium of gastric blind sac is single-layered columnar epithelium. With the exception of gastric blind sac, the mucosa epithelium of digestive tract are double-layered columnar epithelium. There exist abundant goblet cells on the mucosa epithelium, and the quantity of them in the gastric blind sac is most. There are many loosen connective tissue fibers in the submucosa. A great deal of vacuole cells distribute in the submucosa, especially in the foregut submucosa.There are five antisera mammalian like immunoactive endocrine cells in the digestive tract of Branchiostoma belcheri and Styela plicata: 5-hydroxytryptamine (5-HT), gastrin (GAS, subatance P (SP), neuropeptide Y (NPY) and P -endorphin ( -Ep). Differently, somatostatin (SST) immunoactive cells were detected in the digestive tract of Branchiostoma belcheri, but not detected in the digestive tract of Styela plicata. Insulin (Ins) immunoactive cells were not detected in the two animals. Results also showed that feeding and hunger markedly influence the numbers of gastrointestinal endocrine cells of Branchiostoma belcheri. The numbers of 5-HT and SST endocrine cells in hungry animals are more than that in feeding animals. But the numbers of GAS and SP endocrine cells are more in the feeding animals. As regards the other endocrine cells (NPY and -Ep), there are not obvious difference between feeding and hungry Branchiostoma belcheri. There are two kinds of immunoactive endocrine cells in the gastrointestine of Branchiostoma belcheri and Styela plicata: open-type and close-type. The open-type endocrine cells with long or short cytoplasmic protrusion are long column and circular cone in shape; while more close-type endocrine cells are rotundity and ellipse in shape. The morphological and distributional characters of these endocrine cells are related with their different function in the gastrointestine, especially using self-secretion and side-secretion to adjust the gastrointestinal digestion, absorption, peristalsis and the stability of micro environment.