Answer to Question #267529 in Zoology for Amz

Question

Give a comparative account of thyroid of vertebrates

Answer 1

All vertebrates have a thyroid gland. In mammals, it is usually bilobed and located just caudal to the larynx, adjacent to the lateral surface of the trachea. The two lobes may be connected by a fibrous isthmus (eg, ruminants, horses), or a connecting isthmus may be indistinct (eg, dogs, cats). The gland is extremely vascular. In birds, it is found within the thoracic cavity; both lobes are located near the syrinx, adjacent to the carotid artery near the origin of the vertebral artery.

Ectopic or accessory thyroid tissue is relatively common in most species, especially dogs and cats. It may be located anywhere from the larynx to the diaphragm and may be responsible for maintaining normal thyroid function after surgical thyroidectomy. In addition, ectopic thyroid tissue occasionally is the site of hyperplasia or neoplasia.