pinealocytes (or chief cells of the pineal gland). Pinealocytes are modified neurons. Their nuclei are spherical and are relatively lightly stained because of the amount of euchromatin that they contain. The second cell type is the interstitial cell or glial cell that constitutes a relatively small percentage of the cells in the gland. Their nuclei are smaller and more elongate than those of the pinealocytes. The inset reveals several glial cells (G) that can be identified by their more densely staining nuclei. The majority of the nuclei of the other cells seen here belong to pinealocytes. Also seen in the inset are several fibroblasts (F) that are present within a trabecula.
KEY A, artery BS, brain sand C, capillary Cap, capsule CT, connective tissue F, fibroblast G, glial cell L, lobule V, vein
The parathyroid glands are usually four in number. Each is surrounded by a capsule and lies on or is partially embedded in the thyroid gland. Connective tissue trabeculae extend from the capsule into the substance of the gland. The parathyroid glands elaborate a hormone that influences calcium and bone metabolism. Injection of parathyroid hormone into laboratory animals results in the release of calcium from bone by the action of osteocytes (osteocytic osteolysis) and osteoclasts. Removal of parathyroid glands results in a rapid drop in blood calcium levels. The thyroid gland is located in the neck in close relation to the upper part of the trachea and the lower part of the larynx. It consists of two lateral lobes that are joined by a narrow isthmus. The follicle, which consists of a single layer of cuboidal or low columnar epithelium surround-ing a colloid-filled space, is the functional unit of the thyroid gland. A rich capillary network is present in the connective tissue that separates the follicles. The connective tissue also contains lymphatic capillaries.
Parathyroid gland, human, H&E ×320.
As seen here, the larger blood vessels are associated with the trabeculae (BV) and, occasionally, adipose cells (A). The parenchyma of the parathyroid glands appears as cords or sheets of cells separated by capillaries and delicate connective tissue septa.
Two parenchymal cell types can be distinguished in routine H&E sections: chief cells (principal cells) and oxyphil cells. The chief cells (CC ) are more numerous. They contain a spherical nucleus surrounded by a small amount of cytoplasm. Oxyphil cells (OC ) are less numerous. They are conspicuously larger than chief cells but have a slightly smaller and more intensely staining nucleus. Their cytoplasm stains with eosin, and the boundaries between the cells are usually well marked. Moreover, the oxyphils are arranged in groups of variable size that appear scattered about in a much larger field of chief cells. Even with low magnification it is often possible to identify clusters of oxyphil cells because a unit area contains fewer nuclei than a comparable unit area of chief cells, as is clearly evident in this figure. Oxyphil cells appear during the end of the first decade of life and become more numerous around puberty. A further increase may be seen in older individuals.
PARATHYROI D AN D THYROI D G LAN DS KEY A, adipose cells BV, blood vessels CC, chief cells CT, connective tissue F, follicles OC, oxyphil cells arrows, tangential section of follicle wall asterisks, shrinkage artifact
Thyroid gland, human, H&E ×200.
A histologic section of the thyroid gland is shown here. The thyroid follicles (F ) vary somewhat in size and shape and appear closely packed. The homogeneous mass in the center of each follicle is the colloid. The thyroid cells appear to form a ring around the colloid. Although the individual cells are difficult to distinguish at this magnification, the nuclei of the cells serve as an indication of their location and arrangement.