Abstract
ABSTRACT Anatomical and histological examinations were conducted on the digestive glands of two closely related mountain newts, Neurergus microspilotus (Nesterov, 1916) and Neurergus kaiseri Schmidt, 1952. In N. microspilotus and N. kaiseri the major digestive glands comprise a very large liver and a small pancreas. In both species the liver has two distinct lobes, right and left. Histologically, the parenchyma of the liver of both species is contained within a thin capsule of fibroconnective tissue. Glycogen deposits and fat storage often dissolve during the routine histological process and produce considerable histological variability. Sinusoids are lined with endothelial cells forming a very thin epithelial sheet, with discontinuous basement membrane. Bile ducts also occur within the parenchyma of the liver. The ducts are lined by simple cuboidal epithelium. The gall bladder is a storage depot for bile. Its mucosa is thrown into numerous folds. The epithelial lining of the tunica muscularis is arranged circularly. There is a lot of pigmentation in the hepatic parenchyma. The pancreas in N. microspilotus and N. kaiseri is roughly triangular in shape, and lies rather to the dorsal side of the duodenum, between it and the stomach. The exocrine portion of the pancreas consists of clusters of pyramidal cells, which are mostly organized in acini. In both species the cells have a dark basophilic cytoplasm, distinct basal nuclei, and many large eosinophilic zymogen granules containing enzymes responsible for the digestion of proteins, carbohydrates, fats and nucleotides.
Highlights
The digestive system of vertebrates demonstrates various structural and functional adaptations to their diverse feeding habits
The main objective of this study is to describe the digestive gland of two critically endangered mountain newts
Neurergus is phylogenetically closer to the C. orientalis, they are both in the subfamily Pleurodelinae, so it is unusual that the liver of Neurergus resembles that of Salamandra, which is in another subfamily, Salamandrinae
Summary
The digestive system of vertebrates demonstrates various structural and functional adaptations to their diverse feeding habits. The liver and pancreas are major secretory structures that lie across the stomach and duodendum and are derived from the embryonic gut. The liver is the largest of the digestive glands, serving as a nutrient storage organ and producer of bile (Vitt and Caldwell 2009). The gall bladder is intimately associated with the liver in many groups of vertebrates, with a bile duct connecting it to the duodenum. The pancreas is a smaller, diffuse gland. It secretes digestive fluids into the duodenum and its endocrine portion produces insulin (Vitt and Caldwell 2009)
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