General Metabolism of Phosphorus and Calcium

The animal metabolism of P is in large part related to that of Ca, and the Ca/P ratio is believed to affect the absorption and secretion of both of these elements. The dietary Ca/P ratio and its physiological effects has for a long time been a subject of investigation. This ratio, for example, affects the ratio of urinary P/faeces P excreted by the body. The metabolism of P is considerably more complex than that of Ca, and it has more known functions in the body than that of any other single element. 

Ideal bone growth requires not only adequate quantities of Ca and P, but a correct Ca/P ratio and enough vitamin D in the diet, to control the absorption of the two elements. 

The efficiency of absorption of P from food is about 70% for humans, and is given by the expression  

The efficiency of Ca absorption is much lower at around 30%. The P and Ca concentration in the blood is regulated by three substances vitamin D, calcitonin and parathyroid hormone (Chapter 10.2). These substances, the latter two being polypeptides, between them control the absorption of the two elements from the intestine, their deposition and resorption in bone, and 

FIGURE 11,10 General scheme of metabolism of calcium and phosphorus. 

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