Thyroid and parathyroid gland histology
The thyroid gland and parathyroid glands are two distinct endocrine glands located in the neck. The thyroid gland is a butterfly-shaped endocrine gland located anterior and inferior to the larynx. It produces hormones like triiodothyronine, thyroxine, and calcitonin. The parathyroid glands consist of four small ovoid glands located on the posterior surface of the thyroid gland. They are responsible for secreting parathyroid hormone (PTH).
The thyroid is composed of numerous spherical sacs called thyroid follicles. Each follicle is lined by a single layer of follicular cells that synthesize, store, and secrete thyroid hormones (T3 and T4). The colloid, which fills the lumen of the follicles, is composed of thyroglobulin, a glycoprotein that serves as a precursor for the synthesis of thyroid hormones. Parafollicular cells, also called C cells, are located between the follicles and produce the hormone calcitonin, which helps regulate blood calcium levels.
The parathyroid glands are composed of chief cells and oxyphil cells, both of which are responsible for the synthesis and secretion of PTH. PTH helps regulate blood calcium levels by promoting the release of calcium from bones and increasing the reabsorption of calcium by the kidneys. The chief cells are the most numerous and are responsible for most hormone production. Oxyphil cells are larger and less numerous and their function is not well understood.