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

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

• A. Regulates sodium reabsorption
• B. Regulates calcium and phosphate levels
• C. Regulates lactation
• D. Regulates cortisol levels

Answer: (B)

The primary function of parathyroid hormone (PTH) is to regulate calcium and phosphate levels in the body. PTH is secreted by the parathyroid glands and plays a critical role in maintaining serum calcium concentrations within a narrow range, which is essential for various physiological processes, including bone health, nerve function, and muscle contractions.

When serum calcium levels drop, PTH is released into the bloodstream. It acts on several target organs, including the bones, kidneys, and intestines. In the bones, PTH stimulates the release of calcium by promoting the activity of osteoclasts, which break down bone tissue. In the kidneys, PTH enhances the reabsorption of calcium while promoting the excretion of phosphate. Additionally, it boosts the intestines' ability to absorb calcium through its effect on vitamin D metabolism.

This regulatory mechanism is vital, as maintaining calcium levels is crucial not only for metabolic functions but also for preventing conditions like hypocalcemia, which can lead to muscle spasms and other serious health issues. In contrast, the other options pertain to functions that are not directly related to the action of PTH. Sodium reabsorption is primarily regulated by aldosterone, lactation is governed by prolactin and ox