Thyroid and parathyroid gland histology
Thyroid and parathyroid gland histology
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The thyroid gland is a butterfly-shaped endocrine gland with average weight of 25-30 grams, and located anterior and inferior to the larynx.
It produces two types of hormones; the iodine-containing hormones tri-iodothyronine or T3, thyroxine or T4, and calcitonin.
The parathyroid glands consist of four small ovoid glands weigh 30 milligrams each and are located on the posterior surface of the thyroid gland.
They are responsible for secreting parathyroid hormone, or PTH for short.
Let’s first look at the thyroid gland, which has a thin capsule of connective tissue surrounding it that can be seen in this low power image, mostly on the right side.
The connective tissue extends inward along with blood vessels, lymphatics, and nerves.
Although there aren’t any nerves clearly visible in this image.
The thyroid gland is unique because it’s the only endocrine gland that stores its inactive hormones extracellularly in follicles.
The follicles can vary in size quite a lot, from 50 to 500 um.
Each follicle is filled with a gel-like mass called colloid, which stains dark pink with H&E.
The colloid consists mostly of thyroglobulin and thyroid hormones that are bound to the colloid.
We can see that some follicles have colloid with a “scalloped” pale edge.
This is where the follicle has extracted some of the stored colloid in preparation for hormone activation and secretion.
On the other hand, the clear space around the colloid is just an artifact that was caused by the colloid shrinking in comparison to the follicular wall.
The follicular epithelium is made of a single layer of simple cuboidal cells with round central nuclei and dark chromatin.
These cells are responsible for secreting thyroid hormones when needed.
The nuclear features of these cells are particularly important because they are the main feature looked at when diagnosing papillary thyroid carcinoma.
In papillary thyroid carcinoma, the nuclei will be large and irregular with light chromatin, similar to this image, which has pale intranuclear inclusions.
Still at 40x magnification, this image has an example of a parafollicular cell, also called a C cells, near the center.
These pale-stained cells have a granular cytoplasm and are responsible for secreting calcitonin.
They are larger than follicular cells, but there are fewer of them.
They can usually be found in the periphery within the follicular lining, or in the interstitial space between follicles.
Key Takeaways
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.