What is the primary function of parathyroid hormone (PTH)?

The primary function of parathyroid hormone (PTH) is to maintain calcium concentrations in the blood, particularly in relation to bone health and metabolism. PTH is secreted by the parathyroid glands in response to low blood calcium levels. When calcium is low, PTH acts to increase calcium in the bloodstream through several mechanisms: it stimulates the release of calcium from bones, enhances the reabsorption of calcium in the kidneys, and increases the absorption of calcium in the intestines by stimulating the production of active vitamin D.

Maintaining appropriate calcium levels is crucial for various bodily functions, including muscle contraction, nerve transmission, and blood clotting. Hence, PTH plays a vital role in calcium homeostasis and overall metabolic health. The other options do not accurately reflect the specific action of PTH, as growth stimulation, hormone regulation in the ovaries, and processes like binary fission in prokaryotes are unrelated to the hormone's primary roles.