Pharmacology All of the following statements regarding calcium are true except: A It serves as a second messenger for the actions of many hormones. B Intestinal calcium absorption efficiency is directly to calcium intake. C Tubular reabsorption of calcium is regulated by parathyroid hormone. D Ionized calcium in the plasma exerts physiological effects. 💡 Explanation All of the following statements regarding calcium are true except: ✓ Correct Answer: B. Intestinal calcium absorption efficiency is directly to calcium intake.