What hormone is secreted by glands embedded in the posterior thyroid when blood calcium levels drop?

What hormone is secreted by glands embedded in the posterior thyroid when blood calcium levels drop?

• A. Calcitonin
• B. Vitamin D
• C. Parathyroid Hormone
• D. Insulin

Answer: (C)

When blood calcium levels drop, parathyroid hormone (PTH) is secreted by the parathyroid glands, which are small glands located on the posterior surface of the thyroid gland. The primary function of PTH is to regulate calcium and phosphate levels in the blood and bones. It achieves this through several mechanisms: it increases the release of calcium from bones into the bloodstream, enhances renal reabsorption of calcium (reducing its loss in urine), and promotes the activation of vitamin D in the kidneys, which subsequently increases intestinal absorption of calcium from food. This hormonal response is crucial for maintaining calcium homeostasis in the body, as calcium is vital for numerous physiological processes, including muscle contraction, nerve transmission, and blood coagulation. The secretion of parathyroid hormone is part of a feedback mechanism that ensures calcium levels remain within a narrow, optimal range. The other options, while related to calcium metabolism, do not play a direct role in responding to drops in blood calcium levels in the same manner as parathyroid hormone.

When blood calcium levels drop, parathyroid hormone (PTH) is secreted by the parathyroid glands, which are small glands located on the posterior surface of the thyroid gland. The primary function of PTH is to regulate calcium and phosphate levels in the blood and bones. It achieves this through several mechanisms: it increases the release of calcium from bones into the bloodstream, enhances renal reabsorption of calcium (reducing its loss in urine), and promotes the activation of vitamin D in the kidneys, which subsequently increases intestinal absorption of calcium from food.

This hormonal response is crucial for maintaining calcium homeostasis in the body, as calcium is vital for numerous physiological processes, including muscle contraction, nerve transmission, and blood coagulation. The secretion of parathyroid hormone is part of a feedback mechanism that ensures calcium levels remain within a narrow, optimal range.

The other options, while related to calcium metabolism, do not play a direct role in responding to drops in blood calcium levels in the same manner as parathyroid hormone.