The parathyroid glands are four, small glands embedded in the capsule of the thyroid gland. These glands secrete parathyroid hormone (PTH), an essential hormone involved in increasing blood calcium levels. A very thin connective tissue capsule surrounds the parathyroid gland and fine septa extend into the gland. The glands contain two main cell types, chief cells that secrete parathyroid hormone and oxyphil cells that have no known function.

Examine the images at the right and these two examples of parathyroid gland (sample 1, sample 2). Note that the first sample includes thyroid tissue and shows the close association of the two glands. Identify the clusters of chief cells (CC), which secrete PTH. Also, identify oxyphil cells (OC), which are larger and paler staining than the chief cells.
 

Next is the adrenal gland.