The primary role of parathyroid hormone (PTH) is to increase blood calcium levels. It achieves this by stimulating bone resorption, releasing calcium into the bloodstream, enhancing renal calcium reabsorption in the distal tubules, and promoting activation of vitamin D in the kidneys, which increases intestinal calcium absorption. Maintaining adequate blood calcium is crucial for neuromuscular function, blood coagulation, and bone health. Surgically, inadvertent removal or damage to the parathyroid glands can lead to hypocalcemia, a critical postoperative complication.

Reference: Guyton and Hall, Textbook of Medical Physiology, 14th Edition.