How calcitonin decreases plasma Ca2+
Option 1: Calcitonin enhances calcium reabsorption in the kidneys.
Option 2: Calcitonin stimulates osteoclast activity, releasing calcium into the blood.
Option 3: Calcitonin inhibits osteoclast activity, reducing calcium release from bones.
Option 4: Calcitonin has no effect on plasma calcium levels.