Which of the following hormones regulates blood calcium levels?
A.
Parathyroid hormone
B.
Growth hormone
C.
Norepinephrine
D.
Melatonin
The Correct Answer and Explanation is:
The correct answer is A. Parathyroid hormone.
Explanation:
Parathyroid hormone (PTH) is a critical hormone secreted by the parathyroid glands, which are small glands located on the back of the thyroid gland in the neck. PTH plays a vital role in regulating calcium levels in the blood and bone metabolism, making it essential for maintaining the body’s calcium homeostasis.
Function of Parathyroid Hormone:
PTH is released in response to low blood calcium levels (hypocalcemia). It acts primarily on three target organs: bones, kidneys, and the gastrointestinal tract.
- Bones: PTH stimulates osteoclasts, which are cells that break down bone tissue. This process releases calcium from the bones into the bloodstream, increasing blood calcium levels. While this action is crucial for maintaining adequate calcium levels, excessive secretion of PTH can lead to weakened bones and conditions such as osteoporosis.
- Kidneys: PTH reduces calcium excretion by the kidneys, ensuring that more calcium is retained in the body. Additionally, it enhances the conversion of inactive vitamin D into its active form, calcitriol, which further promotes calcium absorption in the intestines.
- Gastrointestinal Tract: Through its action on vitamin D metabolism, PTH indirectly increases the absorption of calcium from the diet in the intestines. This helps to maintain sufficient calcium levels in the blood.
Significance in Health:
The precise regulation of calcium by PTH is vital for many physiological processes, including muscle contraction, nerve function, and blood clotting. Abnormal PTH levels can lead to serious health issues. Hyperparathyroidism, characterized by excessive PTH secretion, results in high blood calcium levels, leading to kidney stones, bone pain, and osteoporosis. Conversely, hypoparathyroidism, marked by insufficient PTH production, causes low blood calcium levels, leading to muscle cramps, tingling sensations, and even life-threatening conditions like tetany, where muscles contract uncontrollably.
In contrast, the other hormones listed—growth hormone (GH), norepinephrine, and melatonin—have different roles. GH regulates growth and metabolism, norepinephrine is involved in the body’s stress response, and melatonin regulates sleep-wake cycles. None of these hormones are directly involved in calcium regulation, which is the primary function of PTH. Therefore, the correct answer is Parathyroid hormone (PTH).