Thyroid Histology

Thyroid Anatomy

Thyroid gland is situated in the anterior aspect of the neck and has
three lobes; right and left conneted by the isthmus, and the pyramidal
lobes which grow from the floor of the mouth. There is a connective
tissue capsule which envelopes the gland, and sends septae into the inner
aspect of the gland, stabilizing the inner endocrine cells.

The thryroid consists of spherical follicles which are made up of
simple squamous to simple columnar epithelium which produce colloid. Colloid
is found within the center of these follicles, which vary in diameter.
Active glands can be identified as the follilces are smaller and the
epithelium taller.

Thyroglobulin

Thyroglobulin glycoprotein is made by these cells and
secreted into the follicles, where it binds oxidized iodide at its
tyrosine residues. TSH stimulates the follicular cells to phagocytose
colloid and release T3 and T4 through lysosomal cleavage, which increase
the basal metabolic rate.

Parafollicular Cells

Parafollicular cells can be found in clusters within connective tissue
of the thyroid gland or alongsinde the follicular cells. Parafollicular
cells are pale-appearing and produce calcitonin which suppresses
osteoclast activity which releases calcium.

Hashimoto's Disease

Hashimoto's diseases, occurs when an antibody blocks and inactivates
the thyroid gland. This leads to an influx of lymphocytes in the gland
and clinically to hypothyroidism. Follicles become replaced by fibrosis
from the inflammation and colloid is absent.