Skeletal System Structure, Mineral Homeostasis (3B) Practice Test

During fasting, a volunteer’s plasma Ca2+ drifts slightly below baseline. The skeleton can restore plasma Ca2+ by increasing osteoclast-mediated bone resorption (releasing Ca2+ and phosphate), while osteoblasts deposit mineral during formation. PTH increases in response to low Ca2+, shifting remodeling toward resorption; calcitonin has the opposite effect. Which change would most directly help restore plasma Ca2+ in this setting?

To study skeletal adaptation, researchers immobilize one leg of adult volunteers for 6 weeks. Bone remodeling maintains mineral homeostasis: osteoclast resorption releases Ca2+ and phosphate (Pi), while osteoblast formation stores them. Reduced mechanical loading tends to shift remodeling toward resorption. PTH promotes resorption when Ca2+ is low; calcitonin inhibits osteoclasts when Ca2+ is high. Based on this setup, which change is most expected in the immobilized limb relative to the loaded limb?