A 30-year-old man comes to the physician because of a 3-month history of pain in his jaw and left arm. He also has had

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A 30-year-old man comes to the physician because of a 3-month history of pain in his jaw and left arm. He also has had intense thirst and increased urination during this period. He was found to have peptic ulcer disease 2 months ago. Physical examination shows no abnormalities. Serum studies show a calcium concentration of 13.5 mg/dl and an intact parathyroid hormone concentration of 110 pg/ml (N=10-65). An x-ray ofthe left humerus shows no abnormalities. Which ofthe following biologic mechanisms best explains the impaired calcium homeostasis in this patient?


A. Decreased calcium reabsorption by renal tubules
B .Decreased expression of parathyroid hormone receptors on osteoblasts
C. Decreased hydroxylation of vitamin D by renal tubule epithelial cells
D. Increased calcitonin secretion by thyroid gland
E. Increased motility of monocytes in bone marrow Increased osteoclast maturation and activity