Which of the following stimulates the release of parathyroid hormone?
Correct Answer: D
Rationale: The correct answer is D: low levels of calcium in the blood. Parathyroid hormone is released in response to low blood calcium levels to help increase calcium levels by promoting its release from bones and enhancing its absorption in the intestines. This response helps maintain calcium homeostasis. TSH from the posterior pituitary gland (choice A) is not related to parathyroid hormone release. High levels of calcium in the blood (choice B) would not stimulate parathyroid hormone release as it is released in response to low calcium levels. Calcitonin from the anterior pituitary gland (choice C) actually works in opposition to parathyroid hormone by promoting calcium deposition in bones and decreasing blood calcium levels.