How do hormones from the parathyroid and thyroid glands influence bone metabolism?

• A. They increase the production of red blood cells in the bone marrow.
• B. They decrease the absorption of calcium in the intestines, leading to weaker bones.
• C. They regulate calcium levels in the blood, affecting bone density.
• D. They stimulate the growth of new bone tissue by increasing osteoblast activity.

Answer: (C)

Verified step by step guidance

1. Begin by identifying the primary hormones involved in bone metabolism from the parathyroid and thyroid glands: parathyroid hormone (PTH) and calcitonin.
2. Understand the role of parathyroid hormone (PTH): PTH is secreted by the parathyroid glands and plays a crucial role in regulating calcium levels in the blood. It increases blood calcium levels by stimulating osteoclast activity, which breaks down bone tissue and releases calcium into the bloodstream.
3. Explore the function of calcitonin: Calcitonin is produced by the thyroid gland and helps lower blood calcium levels. It inhibits osteoclast activity, reducing bone resorption and promoting the deposition of calcium into the bone, thus affecting bone density.
4. Consider the balance between PTH and calcitonin: These hormones work antagonistically to maintain calcium homeostasis. PTH increases blood calcium levels, while calcitonin decreases them, ensuring that bone density is regulated appropriately.
5. Conclude with the impact on bone metabolism: The regulation of calcium levels by PTH and calcitonin directly influences bone density and metabolism. Proper balance between these hormones is essential for maintaining healthy bone structure and function.