SUMMARY FOR YOUR NOTES: - The thyroid appears as an epithelial proliferation of the floor of the pharynx between the tuberculum impar and the copula (that is, between the anterior 2/3 and the posterior 1/3 of the tongue, between the body and root). This location is the foramen cecum. - Thyroid begins as a mass of endodermal tissue! - The thyroid descends in front of the pharyngeal gut as a bilobed diverticulum. Throughout its travel down to the neck, the thyroid remains connected to the tongue by a narrow canal called the thyroglossal duct - which should disappear. - The thyroid travels all the way down to the anterior part of the hyoid bone, and the laryngeal cartilages and reaches its final position in front of the trachea in the 7th week. - By this time, the thyroid should have an isthmus, two lobes, and you have a 50% probability that you have an extra lobe called the pyramidal lobe which you got at this time too. - Follicular cells produced colloid and you might even see some thyroxine being produced at this time. - The parafollicular cells are from the forth pharyngeal pouch - namely from the ultimobranchial body. These C cells produce calcitonin. CONGENITAL ABNORMALITIES: - Thyroglossal cyst - Thyroglossal fistula - Aberrant thyroid tissue #Thyroid #embryology
