How does the body respond to low blood calcium levels?

• A. It stimulates insulin release
• B. It stops producing hormones
• C. It releases parathyroid hormone (PTH)
• D. It increases metabolic rate

Answer: (C)

When blood calcium levels drop, the body responds by releasing parathyroid hormone (PTH) from the parathyroid glands. PTH plays a crucial role in maintaining calcium homeostasis. Its release leads to several physiological responses aimed at increasing blood calcium levels to ensure proper functioning of various bodily processes, particularly those related to the skeletal and nervous systems.

PTH elevates blood calcium levels primarily by promoting the release of calcium from bones, increasing renal reabsorption of calcium in the kidneys, and enhancing intestinal absorption of calcium through its action on vitamin D metabolism. This intricate response is vital because calcium is essential for numerous functions, including muscle contraction, nerve signaling, and blood clotting.

The other options do not directly relate to the body’s mechanism for addressing low blood calcium levels, making them less relevant in this context. For instance, insulin release pertains more to glucose regulation rather than calcium, halting hormone production would impair many bodily functions rather than responding appropriately to low calcium, and increasing metabolic rate, while potentially linked to energy expenditure, does not directly address the need for calcium homeostasis. Thus, the body's primary and immediate response to low blood calcium levels is indeed the release of parathyroid hormone.