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TABLE 9-1 Biological Calcium and Phosphorus


Body content 70-kg man has 1200 g of Ca2+


Structural: bone has 95% of body Ca2+ Plasma [Ca2+] is 9.0-10.2

mg/100 ml (2.2-2.5 mM) Muscle contraction Nerve impulse transmission Blood clotting Membrane structure Enzyme cofactors

(amylase, trypsinogen, lipases, ATPases) Egg shell (birds)

Daily requirements (70-kg man) Dietary intake: 600-1600" Fecal excretion: 300-600" Urinary excretion: 100-300"" Sweat: 100-200"''


Body content

70-kg man has 770 g of P


Structural: bone has 90% of body ^ Plasma [Pi] is 2.1-4.0 mg/

100 ml (0.68-1.1 mM) Intermediary metabolism (phosphorylated intermediates) Genetic information (DNA

and RNA) Phospholipids

Enzyme-protein components (phosphohistidine, phosphoserine) Membrane structure

Daily requirements (70-kg man) Dietary intake: 600-2000" Fecal excretion: 200-600"'6 Urinary excretion: 400-1400"''

" Values in milligrams per day for an adult.

b Based on the indicated level of dietary intake.

interrelationships of absorption by the intestine, accretion and reabsorption by bone tissue, and renal tubular reabsorption and urinary excretion by the kidney.

The three principal endocrine regulators of calcium and phosphorus metabolism are the two peptide hormones parathyroid hormone and calcitonin and vitamin D and its metabolites. The interdependent actions of these three hormones of calcium and phosphorus homeostasis reflect the crucial roles of both calcium and phosphate in the biological processes of higher animals. It is vital that the extracellular calcium ion concentration is maintained within narrow limits; accordingly, the higher the phylogenetic order, the greater the complexity of endocrinological interrelationships and mechanisms developed to ensure ion homeostasis.

The total concentration of calcium in plasma is normally 9.0-10.2 mg/100 ml or 2.2-2.5 mM; consistent deviations outside this narrow "range" of concentrations are reflective of significant perturbations of the calcium-regulating hormones.

Calcium in the plasma exists in three forms: free (ionized), complexed (chelated) by organic ions such as citrate, and protein bound (Table 9-2). Under usual circumstances, ~45% of the total plasma calcium is bound to protein, primarily to albumin, and the remaining 55% is ultrafilterable. There are two basic

TABLE 9-2 Distribution of Calcium and Phosphate in Normal Human Plasma"

Plasma concentration State mmol/liter mg/100 ml'' Percentage of total


Plasma concentration State mmol/liter mg/100 ml'' Percentage of total


Free HP042"

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