Phosphate calcium balance

The Ca(Il) coaceatratioa ia blood is closely coatroUed aormal values He betweea 2.1 and 2.6 mmol/L (8.5—10.4 mg/dL) of semm (21). The free calcium ion concentration is near 1.2 mmol/L the rest is chelated with blood proteias or, to a lesser extent, with citrate. It is the free Ca(Il) ia the semm that determines the calcium balance with the tissues. The mineral phase of bone is essentially ia chemical equiUbrium with calcium and phosphate ions present ia blood semm, and bone cells can easily promote either the deposition or dissolution of the mineral phase by localized changes ia pH or chelating... 

A variety of studies have shown that increasing dietary protein can induce excessive losses of calcium in the urine and a negative calcium balance. This effect is called the calciuric effect of protein. The effect may occur in some persons but not in others. It is most marked with low intakes of calcium and fiigh intakes of protein. Many persons in the United States consume such diets. The calciuric effect of proteins has been demonstrated in a number of controlled studies with human subjects. The effect can be reduced, and perhaps minimized, by phosphate. A simultaneous increase in phosphate intake with protein intake may result in only a small increase in urinary calcium and maintenance of calcium balance. Foods that are high in protein, such as meat and eggs, also contain high levels of phosphate. Thus, the potential hypercalcemic effect of the meat or egg protein may be largely reduced by the phosphate in the same food. 

Normally, 65-80% of filtered calcium and 85-90% of filtered phosphate are reabsorbed, mainly in the proximal tubule. The daily loss of 700-800 mg of phosphate is balanced by dietary intake. Fine-tuning of calcium excretion is accomplished by PTH in the distal convoluted tubules and collecting ducts. Phosphate excretion is regulated by PTH in the proximal tubules. Elevation of the PTH level increases reabsorption of calcium and decreases reabsorption of phosphate from the tubules. This phos-phaturic action opposes the phosphate-sparing action of 1,25-(0H)2D. 

Management of hyperphosphatemia, calcium balance, and secondary hyperparathyroidism includes dietary phosphorus restriction, use of phosphate binding agents, and vitamin D therapy. 

The ionic or free calcium in plasma and serum is associated mainly with chloride ions [46] and represents the calcium that is not bound to protein (normally 30—SS per cent and non-diffusible) or other complexing species such as phosphate, citrate or bicarbonate (normally S-IS per cent and diffusible). In the average healthy person, the calcium ion level is just below one-half of the total and is so closely ibgulated that no gross variability can be detected [47], Furthermore, even in the absence of an adequate calcium intake and a negative calcium balance, plasma calcium remains unchanged for a considerable length of time as the calcium stores in bone are called upon [3,48]. 

Calcium balance studies revealed a positive balance of 80 mg per day, increased absorption from the gut and hypercalciuria. Serum calcium and phosphorus and tubular reabsorption of phosphate were normal. A calcium infusion test gave a normal response. 

Hi) Finally, for tricalcium phosphate, [CaHP04] again is negligible. The calcium balance gives... 

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). 

Vitamin A (845 RE/L) and vitamin D (913 RE/L) may be added to fortify evaporated milk. Other possible ingredients are sodium citrate, disodium phosphate, and salts of carrageenan. Phosphate ions maintain an appropriate salt balance to prevent coagulation of the protein (casein) during sterilization. The amount of phosphate added depends on the amount of calcium and magnesium present. 

PTH has a dual effect on bone cells, depending on the temporal mode of administration given intermittently, PTH stimulates osteoblast activity and leads to substantial increases in bone density. In contrast, when given (or secreted) continuously, PTH stimulates osteoclast-mediated bone resorption and suppresses osteoblast activity. Further to its direct effects on bone cells, PTH also enhances renal calcium re-absorption and phosphate clearance, as well as renal synthesis of 1,25-dihydroxy vitamin D. Both PTH and 1,25-dihydroxyvitamin D act synergistically on bone to increase serum calcium levels and are closely involved in the regulation of the calcium/phosphate balance. The anabolic effects of PTH on osteoblasts are probably both direct and indirect via growth factors such as IGF-1 and TGF 3. The multiple signal transduction... 

J.5 Select an acid and a base for a neutralization reaction that results in the formation of (a) potassium bromide (b) zinc nitrite (c) calcium cyanide, Ca(CN)2 (d) potassium phosphate. Write the balanced equation for each reaction. 

C04-0146. The largest single use of sulfuric acid is for the production of phosphate fertilizers. The acid reacts with calcium phosphate in a 2 1 mole ratio to give calcium sulfate and calcium dihydrogen phosphate. The mixture is crushed and spread on fields, where the salts dissolve in rain water. (Calcium phosphate, commonly found in phosphate rock, is too insoluble to be a direct source of phosphate for plants.) (a) Write a balanced equation for the reaction of sulfuric acid with calcium phosphate, (b) How many kilograms each of sulliiric acid and calcium phosphate are required to produce 50.0 kg of the calcium sulfate-dihydrogen phosphate mixture (c) How many moles of phosphate ion will this mixture provide ... 

C18-0073. For the following salts, write a balanced equation showing the solubility equilibrium and write the solubility product expression for each (a) silver chloride (b) barium sulfate (c) iron(H) hydroxide and (d) calcium phosphate. 

C21-0082. Calcium dihydrogen phosphate is a common phosphoras fertilizer that is made by treating fluoroapatite with phosphoric acid. Hydrogen fluoride is a by-product of the synthesis. Write a balanced equation for the production of this fertilizer and calculate the mass percent of phosphorus in the fertilizer. 

Factors that can predispose patients to developing metabolic bone disease include deficiencies of phosphorus, calcium, and vitamin D vitamin D and/or aluminum toxicity amino acids and hypertonic dextrose infusions chronic metabolic acidosis corticosteroid therapy and lack of mobility.35,39 Calcium deficiency (due to decreased intake or increased urinary excretion) is one of the major causes of metabolic bone disease in patients receiving PN. Provide adequate calcium and phosphate with PN to improve bone mineralization and help to prevent metabolic bone disease. Administration of amino acids and chronic metabolic acidosis also appear to play an important role. Provide adequate amounts of acetate in PN admixtures to maintain acid-base balance. 

Our simple approach to determining the optimal Ca/P ratio for intravenous feeding solutions was to simply alter the ratio of calcium to phosphate in these solutions and measure the only external loss of calcium and phosphate which was in the urine. We initially assumed that the difference between the intake and urinary loss of calcium and phosphate would measure the retention of these elements. The results of seven balance studies at varying Ca/P ratios are shown in Figure 5. 

I he kidneys are sometimes called the master chemists of the body. They work to maintain the constant composition of the hlood hy helping to balance water and the various ions that are present in the blood. A very important equilibrium in the blood, which the kidneys help to control, involves calcium ions and phosphate ions. 

Calcium and phosphate enter the body from the intestine. The average American diet provides 600-1000 mg of calcium per day, of which approximately 100-250 mg is absorbed. This figure represents net absorption, because both absorption (principally in the duodenum and upper jejunum) and secretion (principally in the ileum) occur. The amount of phosphorus in the American diet is about the same as that of calcium. However, the efficiency of absorption (principally in the jejunum) is greater, ranging from 70% to 90%, depending on intake. In the steady state, renal excretion of calcium and phosphate balances intestinal absorption. In general, over 98% of filtered calcium and 85% of filtered phosphate is reabsorbed by the kidney. The movement of calcium and phosphate across the intestinal and renal epithelia is closely regulated. Intrinsic disease of the intestine (eg, nontropical sprue) or kidney (eg, chronic renal failure) disrupts bone mineral homeostasis. 

Milk serum is supersaturated with calcium phosphate, the excess being present in the colloidal phase, as described above. The balance between the colloidal and soluble phases may be upset by various factors, including changes in temperature, dilution or concentration, addition of acid, alkali or salts. The solubility product for secondary calcium phosphate, [Ca2+][HPOr] is about 1.5 x 1(T5 or pKs = 4.85. 

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