116.A 56-year-old man with a history of hypertension, type II diabetes, and
a 2-year history of end-stage renal disease (ESRD) requiring hemodialysis
returns to the internal medicine clinic. The patient is hyperparathyroid
(parathyroid hormone, 234 pg/mL; normal 10–55 pg/mL) and hypercalcemic
(calcium, 12.2 mg/dL). He also has elevated levels of serum urea nitrogen
(52 mg/dL), creatinine (5.2 mg/dL), and hyperphosphatemia (phospho-
rus, 9.1 mg/dL). Serum levels of 1,25-dihydroxyvitamin D are decreased
(10 pg/mL; reference range, 24–65 pg/mL). He has been receiving large
doses of calcium supplemented with vitamin D to bind the phosphate. He
complains of bone and chest pain, increasing fatigue, and extreme dysp-
nea. His coronary arteries are examined by electron-beam computed
tomography (EBCT) and are found to be calcified. The production of cal-
cified soft tissues is mediated by the structures shown in the accompany-
ing transmission electron micrograph. Which of the following is a possible
mechanism of action for those structures?
Specialized Connective Tissues: Bone and Cartilage 201(Micrograph courtesy of Dr. H. Clarke Anderson.)a. Increased secretion of acid phosphatase
b. Inhibition of alkaline phosphatase
c. Accumulation of calcium and phosphate
d. Increased secretion of osteoprotegerin
e. Increased synthesis of type I collagen