Histological Studies on the Mammalian Thyroid Glands

Abstract

The histological observation was made upon the thyroid glands of cows, pigs, horses, cats, dogs, rabbits, guinea pigs and rats by the optical preparations fixed with LEVI's solution and stained with HEIDENHAIN's iron hematoxylin. The results principally concerning the internal structure of glandular cell and parafollicular cell were as follows.It was a tendency common to various animals that the follicles was increased in size at the peripheral area of the gland, and decreased to be immature at the central part. The large follicles with the cytological feature of inactive partipation in colloidal formation and reabsorption because of the flattened epithelium would appertain to be storage type, whereas small follicles are provided with the elongated epithelial cells which would perform the synthersizing and releasing functions. In general, the discharge of intracellular thyroglobulin was capable by means of the secretory mechanism coincided with that in the protein cells of exocrine glands, while the apocrine secretion in thyroid gland cell, frequently occurring in cows, horses and rats but never or seldom take places in remaining animals, might be analogous to so-called hunger secretion caused under the extraordinarily strong and contineous stimuli. It is author's opinion that the vacuoles appearing at the supranuclear region are the ultimate products within the cell-body which may be eliminated through the cell membrane by a certain way, not by an apocrine secretion. It was comprehensive in present observation that the circumference vacuoles was not only derived from the diffusion of vacuoles in the cytoplasmic projection which may perform an apparent apocrine secretion, but also from the accumulation of tiny vacuoles directly eliminated through the cell membrane. The intercellular discharging canaliculi frequently observed in human thyroid gland (ITO 1955) were not sufficiently developped in these mammals with the exclusion of rats. The huge colloidal substances with various contour seen in some locations of cytoplasm, focusing at the apical parts, were typical in cows in spite of the ignorance of their functional significance, however evidences were presented that they may be responsible for the intracellular colloids which was not synthesized in the cell-body. Notwithstanding the animal differences in characteristics of parafollicular cells, they were able to be recognized through all kinds of animals, and the mode of the cell population accounted for enough morphologicbl basis to enable to assume a connection to proliferation or neoformation of follicles, but in some animals it was not apparent whether they could play a principal role in neoformation because of the difficult identification of them.It was only in the rat that the parafollicular cells were equipped with the morphological criteria showing an intimate relathionship to the thyroxin production or basal section. In case of their proliferation, they were, in all mammals, so increased in number within the thickened wall of follicular epithelium as the nodules that they vulged toward the interspace, thereafter the constriction of the neck of their protrution was followed by the separation from the mother follicles, that is a neoformation of the follicles.