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Slide #DMS 161 [Thyroid & Parathyroid, monkey, H&E]. Look for a parathyroid gland embedded in this section of thyroid gland. The gland consists mostly of closely-packed cords or clumps of small, basophilic, secretory chief (principal) cells. The gland has a connective tissue capsule of its own. Connective tissue stroma is minimal but contains many blood capillaries. Look for small clusters of larger, eosinophilic oxyphil cells. These cells usually do not appear until after puberty, and increase in numbers with age. Their function is still uncertain. Finally, check out the well-preserved brown adipose tissue and myelinated nerve trunks in the adnexal tissue.

This is a very low power view of a section through a thyroid gland, in the midst of which is found a parathyroid gland. The location of the parathyroids is variable, sometimes being found in the midst of the thyroid parenchyma as seen here, sometimes sharing a capsule with the thyroid, or alternatively, within their own connective tissue capsule on the periphery of a thyroid gland.

At higher power, the marked difference in histological architecture between the thyroid gland and the parathyroid is obvious. Again, the thyroid tissue is characterized by colloid-filled follicles, while the parathyroid is represented by a dense, and, at this magnification, seemingly homogeneous population of endocrine cells, seen to better effect in the next image.

A high power view of the parathyroid reveals two major cells types, the small chief cells characterized by rather scant, lightly-stained cytoplasm, and the much larger, eosinophilic oxyphil cells, which are often found in small clusters. The chief cells are responsible for the production of parathyroid hormone, while the function of the oxyphil cells is not known.

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