Figure 3.

Anatomic sites of calcium flux. The figure shows the major sites of calcium flux in the body with indication of the average amounts of daily calcium flux. Dietary (D) calcium (Ca) undergoes net absorption (a) through the intestine into the extracellular fluid (ECF). Daily bone resorption (Br) and formation (Bf) are equal. The filtered load (FL) of calcium is substantially reabsorbed (fr, fractional reabsorption) in the kidney, resulting in urine (U) calcium excretion that is virtually identical to the amount absorbed in the intestine (reproduced with permission from Frick and Bushinsky, ref. 63).