PTH secretion causes the release of calcium from the bones by stimulating osteoclasts, which secrete enzymes that degrade bone and release calcium into the interstitial fluid. The parathyroid glands produce and secrete PTH, a peptide hormone, in response to low blood calcium levels ( Figure 17.5.2). View the University of Michigan WebScope at to explore the tissue sample in greater detail. (Micrograph provided by the Regents of University of Michigan Medical School © 2012) Figure 17.5.1 – Parathyroid Glands: The small parathyroid glands are embedded in the posterior surface of the thyroid gland. These epithelial cells produce and secrete the parathyroid hormone (PTH), the major hormone involved in the regulation of blood calcium levels. The gland also contains oxyphil cells but their function is not clear. The primary functional cells of the parathyroid glands are the chief cells. Most people have four parathyroid glands, but occasionally there are more in tissues of the neck or chest. A thick connective tissue capsule separates the glands from the thyroid tissue. The parathyroid glands are tiny, round structures usually found embedded in the posterior surface of the thyroid gland ( Figure 17.5.1).
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