Morphological and Ultrastructural Study of Selected Endocrine Gland (thyroid, Ultimobranchial, and Adrenal) in Egyptian Turkeys (meleagris Gallopavos).

The thyroid, ultimobranchial, and adrenal glands are major endocrine organs in birds, essential for regulating various physiological functions. This study presents a comprehensive morphological and ultrastructural investigation of these three glands in adult male Egyptian turkeys using light microscopy, and transmission electron microscopy (TEM). The thyroid and ultimobranchial glands are in the thoracic cavity near the trachea, while the adrenal glands are positioned adjacent to the caudal vena cava and cranial poles of the kidneys. Histologically, the thyroid follicles are lined by simple cuboidal to columnar epithelium. The ultimobranchial gland appears as a single-lobed structure encased in a thick capsule and composed of C-cell follicles and cords. These C cells exhibit light and dark variants, with ultrastructural evidence of secretory granules, abundant vacuoles, and active rough endoplasmic reticulum. The adrenal gland is encapsulated by a thick layer of connective tissue. Its parenchyma showed intermingled interrenal and chromaffin cells, with the former arranged in multilayered follicles. Chromaffin cells formed large clusters and are distinguished into epinephrine and norepinephrine types by ultrastructure and Grimelius silver staining. These findings contribute valuable insights into the comparative avian endocrinology and structural adaptations of the turkey's endocrine organs.