Final answer:
Calcitriol, parathyroid hormone, and calcitonin are hormones that regulate calcium status, playing a vital role in maintaining balance by affecting the bones, kidneys, and intestines to control blood calcium levels.
Step-by-step explanation:
Calcitriol, parathyroid hormone, and calcitonin regulate calcium status. Therefore, the correct answer is A. calcium. These hormones play a crucial role in maintaining calcium homeostasis.
Parathyroid hormone (PTH), produced by the parathyroid glands, responds to low blood calcium levels by increasing bone resorption, enhancing reabsorption of calcium by the kidneys, and stimulating the activation of vitamin D which aids in the absorption of calcium from the intestines. Calcitriol, the active form of vitamin D, also promotes calcium absorption in the intestines.
Calcitonin, produced by the parafollicular cells of the thyroid gland, helps to lower elevated blood calcium levels by inhibiting osteoclasts, stimulating osteoblasts, and increasing excretion of calcium by the kidneys, which adds calcium to bones and promotes structural integrity.