Figure 7. Disordered calcium homeostasis in granulomatous disease. Production of an extra-renal 1(OH)ase by macrophages in a granuloma can increase conversion of circulating 25(OH)D3 to 1,25(OH)2D3. This secosteroid will increase Ca+2 absorption from the gut and Ca+2 resorption from bone resulting in an increased ECF Ca+2. The increased ECF Ca+2 and 1,25(OH)2D3 will inhibit PTH production by the parathyroid glands. The increased filtered load of Ca+2 through the kidney and suppressed PTH will contribute to hypercalciuria.