Anatomical and Histochemical Studies of the thyroid gland of two Egyptian reptiles

Abstract

Two species of lizards are used in the present work Eumeces schneiderii as a hibernating reptile and Laudakia stellio brachydactyla as a non-hibernating one. Macroscopically, the thyroid of Eumeces schneiderii is formed of separate paired structures lying on both sides of the bifurcation of left and right carotid arteries. The thyroid of Laudakia, is formed of two well defined lobes each lying on either side of the trachea with a narrow connecting isthmus. Microscopically, the thyroid gland in both animals is composed of a big number of follicles which are held together by a loose connective tissue. The Interfollicular spaces are filled with blood sinusoids. Each follicle is composed of one layer of epithelial cells, which vary in their heights from winter to summer. In Laudakia, the gland never become completely inactive during winter. In Eumeces schneiderii , it is completely inactive during hibernation. Intracellular colloid droplets are rarely found in the thyroid of Laudakia, while they are very frequent In Eumeces schneiderii. This colloid shows regular seasonal changes in both animals depending on the degree of activity of acini.