|General Gross Description|
•The thyroid originates as an invagination of the
epithelium covering the base of the tongue.
•This invagination extends caudally as the thyroglossal
•On reaching the area caudal to the larynx, the
thyroglossal duct expands to give rise to the bilobed
structure of the thyroid.
•The thyroglossal duct may persist in adulthood,
extending rostrally in the median line from the
isthmus linking the 2 lobes of the thyroid.
•These may be found anywhere between the isthmus of the
thyroid and the tongue as cysts or aberrant thyroid
•Grossly, the thyroid is a deeply orange/brown structure, faintly lobulated in appearance.
•It weighs approximately 30 grams in the adult, and is
somewhat larger in females in whom it can become
significantly larger during pregnancy and lactation.
•On cut surface, the organ is a glassy, deep orange/brown, with some evidence of lobulation.
|General Micro Description|
•Microscopically, the thyroid is composed of innumerable
spherical acini or follicles.
•The follicles of the thyroid are lined by cuboidal
epithelium in a normal resting thyroid gland.
•The cells are uniform in appearance.
•In a very active thyroid, the cuboidal epithelium can
appear more columnar.
•Lying within the follicles is material that stains
deeply eosinophilic in standard H&E preparations.
•In a resting thyroid, this deeply eosinophilic material,
called colloid, is in contact with the lining
epithelial cells around the circumference.
•In an active thyroid, however, the rim of the colloid
•This appearance is indicative of hyperactivity of
the thyroid gland.
•In addition to the cells lining the thyroid, additional
cells called C cells are distributed both among and
between the lining cells.
•These cells, also known as the parafollicular cells, secrete calcitonin.
|Bloom and Fawcett: A textbook of Histology. 12th
Edition. Chapman & Hall. 1994. pp 490
Gray: Gray^s Anatomy. 15th Edition. Barnes & Noble
Books. 1995. pp 964 et seq.|