Thyroid gland


Magnification 1

Thyroid gland

The thyroid gland is an endocrine organ located to the anterior lower portion of the neck. It is involved in regulation of metabolism and the blood calcium levels. Thyroid hormone is produced in response to elevated pituitary TSH levels. An other hormone produced by the thyroid gland, calcitonin, is produced in response to elevated blood calcium levels.

The thyroid gland has lobular organization. The numerous thyroid follicles form the secretory units of the thyroid gland. The follicles are spherical and lined with a single layer of cuboidal epithelial cells, follicular cells. The thyroid gland is rich in blood supply and a vascular network surrounds each follicle. Thyroglobulin is stored in homogeneous eosinophilic colloid material which is typically abundant within the thyroid follicles. In response to increased blood TSH levels, thyroid hormone is reabsorbed from the colloid and released into the blood. In addition to the dominating thyroid follicles, groups of cells with a slightly more eosinophilic cytoplasm are present, that resemble the calcitonin producing parafollicular cells.

Cancer: Thyroid cancer