Morphology of the thyroid gland and oxidoreductases in the liver of mithuns (Bos frontalis) and yaks (Ros grunniens)

Abstract

Thyroid glands and livers from 3 adult mithuns and 3 adult yaks were studied. The topography, gross anatomical features andmicroscopic features of the thyroid gland and histochemical localizalion of oxidoreductases in the liver were recorded. Thegross appearence of both the thyroid glands of mithuns was elongated and elliptical, whereas in yaks the right lateral lobewas triangular in shape and the left one cashewment shaped. The thyroids of mithun extended  from the level of cricoidcartilage up to the tracheal ring 4, while in yak it was located just caudal to the larynx up to tracheal ring 2 or 3. Theisthmus was more distinct and glandular in mithuns than in yak. Thyroids of mithunss revealed comparatively higher biometriccharacteristics in length, width, thickness and weight than of yaks. The capsule of the gland in both the species wasdouble-layered with predominance of collagenous fibres in it and trabeculae. The average mean diameter of the thyroidfollicles did not show remarkable variations between mithuns (89.60±7.06 µm) and yaks (92.80±6.60µm). The follicular liningepithelium was simple squamous with PAS - positive basement membranes and colloid. The para follicular cells were marked assingle or double in both the species. The oxidoreductases in the liver of mithuns and yaks comprised of succinate-, lactate-,glucose-6-phosphate dehydragenases, cytochrome- and monomine oxidase, These were localized in biliary epithelium. vascularendothelium and hepatocytes. The hepatocytes in lhe liver of these large ruminants contained all above enzymes with arelatively higher concentration in mithuns.