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1. Which of the following hormones is primarily involved in the regulation of blood calcium levels? A. Insulin B. Thyroxine C. Parathyroid hormone D. Cortisol Answer: C. Parathyroid hormone Rationale: Parathyroid hormone (PTH) is released by the parathyroid glands and plays a critical role in maintaining calcium homeostasis by increasing blood calcium levels. 2. The bundle of His is an integral part of which human body system? A. Respiratory system B. Digestive system C. Cardiovascular system D. Nervous system
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