How do the thyroid and parathyroid glands form a feedback loop in the regulation of calcium levels in the blood?

• A. The thyroid gland releases thyroxine to increase blood calcium levels, while the parathyroid glands release calcitonin to decrease blood calcium levels.
• B. The thyroid gland releases calcitonin to lower blood calcium levels, while the parathyroid glands release parathyroid hormone to increase blood calcium levels.
• C. The thyroid gland releases parathyroid hormone to increase blood calcium levels, while the parathyroid glands release thyroxine to decrease blood calcium levels.
• D. The thyroid gland releases calcitonin to increase blood calcium levels, while the parathyroid glands release thyroxine to decrease blood calcium levels.

Answer: (B)

Verified step by step guidance

1. Identify the primary hormones involved in calcium regulation: calcitonin and parathyroid hormone (PTH).
2. Understand the role of the thyroid gland: it releases calcitonin, which helps to lower blood calcium levels by inhibiting osteoclast activity and promoting calcium deposition in bones.
3. Understand the role of the parathyroid glands: they release parathyroid hormone (PTH), which increases blood calcium levels by stimulating osteoclast activity, increasing intestinal calcium absorption, and promoting renal calcium reabsorption.
4. Recognize the feedback loop: when blood calcium levels are high, the thyroid gland releases calcitonin to decrease calcium levels. Conversely, when blood calcium levels are low, the parathyroid glands release PTH to increase calcium levels.
5. Clarify the incorrect statements: the thyroid gland does not release thyroxine to regulate calcium levels, and the parathyroid glands do not release calcitonin. The correct hormones are calcitonin from the thyroid and PTH from the parathyroid glands.