author(s)
Dinesh Kumar, R Vaish, Y Pandey, N Gupta, Umeel and Pratyush Kumar

abstract
The thyroid is an endocrine gland lies in the neck, in front of the upper part of the trachea. The thyroid term is derived from Greek word ‘thyreos’ and ‘eidos’. 'Thyreos' means an oblong shield and ‘eidos’ means form, because its shape is like a shield. The gland is enclosed in a connective tissue capsule that is continuous with the surrounding cervical fascia. Gland is composed of large number of follicles of various sizes. The follicles are spherical in shape and lined by a single layer of epithelium. These cells are simple cuboidal or short columnar depending upon their size and content i.e. colloidal substance called thyroglobulin. The small sized follicles are lined by high simple cuboidal, medium sized follicles are lined by very low simple cuboidal, while the large sized follicles have low simple cuboidal and even squamous epithelium in some very large follicles. The thyroid gland is the first glandular structure to form. Initially it develops as an exocrine gland.