Why does parathyroid hormone (PTH) secretion generally increase bone mineral resorption when blood calcium levels are low?

💡 Explanation

PTH increases bone mineral resorption because it activates osteoclasts indirectly via osteoblasts expressing RANKL, thereby promoting calcium release from bone to increase blood calcium levels. Therefore, stimulating osteoclast activity is the correct response, rather than actions on osteoblasts, renal reabsorption or phosphorus absorption.

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