Fine Structure of the Ultimobranchial Gland in the Chick

Abstract

Although the ultimobranchial gland of the chick has been shown to contain large amounts of calcitonin relatively few reports have been published on its fine structure. In the present study, the ultrastructure of the chick ultimobranchial gland, with emphasis on the cells which appear to be the producers of the hormone, will be examined. Ultimobranchial glands were obtained from twenty 2-week-old chicks and fixed in glutaraldehyde followed by osmium tetroxide.The gland is composed of aggregate of cords and clusters of cells interspersed with variable numbers of cyst-like cavities. Two parenchymal cell types, namely, light and dark cells can be recognized (Figs. 1,2,3). Epithelial cells, varying from columnar to cuboidal, line the cavities of the cysts.Light cells form the majority of the cell types (Fig. 1). The cytoplasm is characterized by the presence of membrane-limited secretory granules, measuring from 100 to 350 mμ in diameter. The contents of the secretory granules vary in electron density from moderate to extreme (Figs. 1,2). Secretory granules are distributed randomly in the cytoplasm although some are lined near the cell membrane.