7.13: The Parathyroid Glands

Essentials of Physiology for Nurse Anesthetists (Gopalan) · LibreTexts

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    Diagram of the parathyroid glands located behind the thyroid, with a microscopic view showing chief cells and blood vessels within the parathyroid tissue.
    Figure 22 | Parathyroid Glands | ​22 This figure illustrates the anatomical location and histological features of the parathyroid glands. The parathyroid glands are typically situated on the posterior surface of the thyroid gland, with four glands commonly found (two on each side). Histologically, the parathyroid glands are composed of two main cell types: chief cells and oxyphil cells. Chief cells, which are smaller and more numerous, are responsible for producing parathyroid hormone (PTH), essential for calcium regulation. Oxyphil cells, larger and less abundant, are thought to play a role in the aging process of the glands.

    The parathyroid glands, petite, circular structures nestled within the connective tissue enveloping the posterior aspect of the thyroid gland (Figure 22), play a pivotal role in the intricate regulation of calcium levels within the body. While typically four parathyroid glands are present, exceptions with additional glands within the neck or chest tissue may occur. Although closely associated with the thyroid gland, parathyroid glands maintain a degree of separation through a robust connective tissue capsule. These glands comprise chief cells as their primary functional units. Within these epithelial cells, an 84-amino acid-containing polypeptide hormone, PTH, also known as parathormone, is synthesized and secreted. PTH takes center stage as the principal hormone orchestrating the control of blood calcium ion concentrations. It initiates a gradual release of calcium ions from bones by stimulating osteoclasts. The effect of PTH on osteoclast is indirect. PTH affects osteoclasts by stimulating osteoblasts to secrete RANKL, which promotes osteoclast differentiation. PTH facilitates the increased reabsorption of calcium (and magnesium) ions within the renal tubules, ensuring these ions are retained within the body. It prompts increased phosphate excretion at the renal tubules to prevent the utilization of calcium ions in bone matrix deposition. PTH initiates the production of calcitriol, also known as 1,25-dihydroxyvitamin D, the active form of vitamin D3. Calcitriol stimulates heightened absorption of dietary calcium and phosphate ions by the intestines. Additionally, PTH generally increases the expression of calcium-binding proteins, especially in tissues like the kidneys and intestines, to enhance calcium absorption and retention.

    A sophisticated negative feedback mechanism finetunes PTH levels. As blood calcium ion concentrations rise, they exert an inhibitory effect on further PTH release (Figure 23). Conversely, low levels of magnesium ions can stimulate PTH secretion. However, it is noteworthy that chronic hypomagnesemia may impair the parathyroid gland's proper function, potentially leading to hypocalcemia in severely hypomagnesiemic individuals.

    Flowchart detailing pressure injury stages with diagrams. Includes skin layers, pressure effects, ulcer stages, and healing processes. Arrows indicate progression from stage 1 to 4 and treatments.
    Figure 23 | The Interplay of Calcitonin and Parathyroid Hormone in Maintaining Blood \(\ce{Ca2+}\) Homeostasis | ​23  This figure depicts the role of parathyroid hormone (PTH) in regulating blood calcium levels. PTH, produced by the chief cells of the parathyroid glands, is released in response to low blood calcium concentrations. The figure illustrates three primary mechanisms through which PTH maintains calcium homeostasis: PTH stimulates osteoclast activity, promoting the release of calcium from bones into the bloodstream, enhances renal tubular reabsorption of calcium, reducing urinary calcium excretion and ensuring more calcium is retained in the body, and indirectly increases intestinal calcium absorption by stimulating the conversion of vitamin D to its active form, calcitriol. This figure also summarizes the role of calcitonin in regulating blood calcium levels. Its main effect is to inhibit the action of osteoclasts. 

    This page titled 7.13: The Parathyroid Glands was last modified on Wed, 19 Mar 2025 23:12:03 GMT and is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Chaya Gopalan (Consortium of Academic and Research Libraries in Illinois (CARLI)) .