Calcium absorption physiological effects

Local conditions in the intestinal lumen also influence calcium absorption. The concentration of the metal in the intestinal content increases calcium absorption. Saccharides and disaccharides accelerate calcium absorption in the ileum by a mechanism that is not yet understood. This effect is of physiological significance only in the case of milk, which is rich... 

Phosphate balance in adults is almost always zero, in contrast to calcium balance, which is usually negative, because of the effective action of PTH on renal tubules to block Pi reabsorption. In late life, however, intestinal phosphate absorption decreases and the serum phosphate concentration declines. These physiological decrements may contribute to disease, especially to increased bone loss and osteopenia or more severe osteoporosis. Typically, these changes in Pi balance are also accompanied by similar changes in calcium balance. Too little dietary phosphorus and too little dietary calcium may be determinants of low bone mass and density and, hence, increased bone fragility. The usual scenario invoked to explain osteoporosis in old age, however, is that too little dietary calcium in the presence of adequate dietary phosphorus stimulates PTH release and bone loss (Figure 1). 

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