The hormone that stimulates calcium deposition into bone is:
A.
Calcitonin.
B.
Parathyroid hormone.
C.
Thyroxine.
D.
Insulin.
The Correct answer and Explanation is:
Correct Answer: A. Calcitonin
Explanation:
Calcitonin is a hormone produced primarily by the parafollicular cells (also known as C cells) of the thyroid gland. Its primary function is to regulate calcium homeostasis in the body, particularly by lowering blood calcium levels when they become elevated. Calcitonin achieves this by promoting the deposition of calcium into bone, thereby reducing the amount of calcium in the bloodstream.
Mechanism of Action: Calcitonin acts by inhibiting the activity of osteoclasts, the cells responsible for bone resorption. Osteoclasts break down bone tissue, releasing calcium and phosphate into the bloodstream. By suppressing osteoclast activity, calcitonin reduces bone resorption, which in turn decreases the release of calcium into the blood. Additionally, calcitonin promotes the activity of osteoblasts, the cells that build up bone tissue by depositing calcium and other minerals into the bone matrix.
Role in Calcium Homeostasis: The balance between calcitonin and parathyroid hormone (PTH) is crucial for maintaining calcium homeostasis. While calcitonin lowers blood calcium levels, PTH increases blood calcium levels by stimulating osteoclast activity, promoting calcium reabsorption in the kidneys, and enhancing calcium absorption in the intestines through the activation of vitamin D. These opposing actions help to tightly regulate calcium levels in the blood.
Clinical Applications: Calcitonin is sometimes used therapeutically to treat conditions like hypercalcemia (excessive calcium in the blood), Paget’s disease of bone (a condition characterized by abnormal bone remodeling), and osteoporosis (a condition where bones become weak and brittle). In these cases, synthetic forms of calcitonin can help lower blood calcium levels and promote bone formation.
Other Hormones:
- Parathyroid Hormone (B): This hormone has the opposite effect of calcitonin, raising blood calcium levels by increasing bone resorption.
- Thyroxine (C): A thyroid hormone primarily involved in regulating metabolism, with no direct role in calcium homeostasis.
- Insulin (D): A hormone that regulates blood glucose levels and has no direct effect on calcium metabolism.
In summary, calcitonin plays a vital role in calcium homeostasis by promoting the deposition of calcium into bones and lowering blood calcium levels, which is crucial for maintaining bone strength and overall health.