Histological Study Of The Digestive System Of Hynobius Maoershanensis And Pachytriton Intexpectatus

Food is one of the basic conditions for animal survival.The digestive system of animals is an important place on food processing and utilization,which structure is adapted to their eating habits.Amphibians living in Guangxi Maoershan National Nature Reserve may develop unique adaptive strategies due to the complicated water system pattern,special geographical environment and climate characteristics.In this study,we studied the structure of the digestive system of Hynobius maoershanensis and Pachytriton intexpectatus living in Guangxi Maoershan National Nature Reserve,northeast of Guangxi,China,to explore the characteristics of structure and function of the digestive system,and how their digestive system and endocrine cells adapt to eating habits and living environment.HE,Grimelius and immunohistochemical staining and other techniques were used.This paper aimed to accumulate the basic biological data for studying the morphology,histology and endocrinology of the digestive system of urodele amphibians.The experimental results were as follows:1.Observation of the morphological structure of the digestive system showed that the digestive tracts of H.maoershanensis and P.intexpectatus were similar to that of other amphibians,which were composed of esophagus,stomach,duodenum,ileum and rectum.Both the esophagus were short and thick,and the stomach was spindle-shaped.The length of digestive tract and the ratio of intestine length and snout-vent length(IL/SVL)of P.intexpectatus was 109.86 ± 5.49 mm and 0.84 ± 0.03,respectively,which were significantly higher than that of H.maoershanensis.The liver of both was dark brown and divided into the right and left lobes.2.Histological observation of the digestive system showed that the digestive tract of H.maoershanensis and P.intexpectatus could be divided into mucosa,submucosa,muscularis and adventitia.The thickness of the mucous layer and muscular layer in each part of the digestive tract were significantly different.The thicknesses of mucosa in the stomach body of H.maoershanensis was 712.82 ± 37.67 ?m,which was significantly higher than that of P.intexpectatus.The thickest of the muscular layer of H.maoershanensis and P.intexpectatus were 398.76 ± 16.91 ?m and 439.45 ± 27.86 ?m,respectively,which was located in the pylorus.Glisson capsule,central veins,portal areas and hepatic cells constituted the liver structure in both of them.The hepatocyte clusters or cords were arranged in an indistinct radial pattern around the central vein.Many brown-black melanin granules could be seen in the liver parenchyma.3.Grimelius staining results showed that argyrophil cells were found to be distributed among the epithelial cells of the mucosa or glands throughout the digestive tract of H.maoershanensis and P.intexpectatus.These cells had various shapes,including round,oval,spindle,cone,etc.,which could be divided into two types: closed type and open type.The highest density of argyrohil cells of both was found in the esophagus,with distribution densities of 2.00 ± 0.69 and 3.42 ± 0.31,respectively.The least density of argyrohilic cells of H.maoershanensis was in the ileum,while P.intexpectatus was in the rectum.4.Immunohistochemical staining results showed that the open and closed 5-HT cells were distributed throughout the digestive tract of H.maoershanensis and P.intexpectatus,mainly distributed between the epithelial cells of the mucosa or glands,with round,oval and spindle cells were widely distributed.The distributional pattern of 5-HT cells along the digestive tract of both was different.The part of the highest density of 5-HT cells in H.maoershanensis was in the rectum,but P.intexpectatus was in the duodenum.And the least density of 5-HT cells in H.maoershanensis was in the esophagus,while P.intexpectatus was in the rectum.5.AB-PAS staining results showed that the digestive tracts of H.maoershanensis and P.intexpectatus contained mucous cells.There were types?,?,? and ? mucous cells in the digestive tract of H.maoershanensis,but P.intexpectatus contained types ?,? and? mucous cells.There were similarities and differences in the types of mucous cells in the digestive tract between both of them.The mucous cells of the esophagus were mainly typed ? of both,but H.maoershanensis had type ?,?,? and ? cells,P.intexpectatus only contained type ? cells.Both the stomach body and pyloric of mucous cells were type?,but the types of mucous cells in the cardia were different.Type ? and ? cells were distributed in the cardia of H.maoershanensis,and P.intexpectatus included type ? and? cells.What' s more,the type ? cells were distributed throughout the gut of H.maoershanensis and P.intexpectatus.6.Dietary analysis showed that: 10 food species in 8 categories were identified in the digestive tract contents of H.maoershanensis by high-throughput sequencing,including crytophyceae,amoebozoa,ciliophra,spironemidae,meramonada,annelida,arthropoda,amphibian.And 16 food species in 7 categories were identified of P.intexpectatus,including chrysophyceae,ciliophra,alveolata,platyhlminthes,annelida,arthropoda,amphibian.Conclusion: The histological structure of the digestive system in H.maoershanensis and P.intexpectatus was similar to that of other amphibians,which had the structural characteristics of carnivorous animals.For example,the ratio of intestine length and snout-vent length of them was no more than 1,which was consistent with the characteristics of the short digestive tract of carnivorous animals.The presence of animals was also detected in the dietary analysis,which further provided evidence for both to prey on animal food.The histology structure of the digestive tract showed that many characteristics adapted to food digestion and nutrient absorption.Both liver parenchymal melanin granules were compatible with their living environment.The distributive pattern of argyrophilic,5-HT and mucous cells of both had their own characteristics,and the morphology of these cells was adapted to the physiological function of the digestive tract.The difference in distribution characteristics was related to the living environment,feeding habit,food composition and other factors.