Maintenance of body calcium memory (hypocalcemia or hypercalcemia and avoid) depends on
Calcium is for the regular functioning of muscle contraction, nerve transmission, hormone secretion and blood clotting is important. In addition, a real concentration of calcium for various other metabolic processes is needed. Maintenance of body calcium memory (hypocalcemia or hypercalcemia and avoid) depends on absorption of calcium in the diet calcium absorption in the gastrointestinal tract Renal calcium excretion over a balanced diet are daily added about 1,000 mg of calcium and 200 mg / day in the gastrointestinal tract over given the bile and gastrointestinal secretions. Depending on the concentration of circulating parathyroid hormone (PTH) and active vitamin D, 1,25 (OH) 2D (dihydroxycholecalciferol 1.25, calcitriol) can be absorbed about 200-400 mg of calcium from the intestine every day. The remaining 800-1000 mg appear in the stool. The calcium balance is obtained by urinary excretion of calcium, an average of 200 mg / day, which also depends on circulating PTH and calcitonin levels. Both the intra- and extracellular calcium concentrations by the bidirectional transport of calcium across the plasma membranes of cells and intracellular organelles such as the endoplasmic reticulum, the sarcoplasmic reticulum of muscle cells and the mitochondria, very tightly regulated. Ionized calcium is the physiologically active form. In the cytosol of the ionized calcium content in the micromolar range (<1/1000 of the serum concentration) is maintained. Ionized calcium is an intracellular second messenger. It plays a role in skeletal muscle contraction, in the coupling between excitation and contraction in the myocardium and in smooth muscle cells and in the activation of protein kinases and enzymatic phosphorylation. Calcium is also involved in the effects of other intracellular messengers. Examples include cAMP, inositol 1,4,5 triphosphate and messengers that the cellular response to a variety of hormones such. give as adrenaline, glucagon, vasopressin (vadh, secretin and cholecystokinin. In addition to its important intracellular role about 99% of the calcium contained in the body is stored in bones, mainly as hydroxyapatite. About 1% of the data stored in the bone calcium is the ECF-free interchangeable and is thus located from 8.8 to 10.4 mg / dL (2.20-2.60 mmol / l). Approximately 40% of the total calcium in the blood to compensate for changes in calcium balance available. Normal serum total calcium concentration are bound to plasma proteins, mainly albumin. the remaining 60% of the ionized calcium and calcium complexes include phosphate and citrate. the total calcium (protein-bound, located in the complex and ionized) is normally that which is measured in clinical laboratories. However, it should ideally be estimated ionized (or free) calcium or measured, because it is the physiologically active form of Kalz ium is in plasma and because his blood levels do not always correlate with the total serum calcium. Under normal conditions, it is believed that the ionized calcium is about 50% of the total serum calcium. Ionized calcium can based on the total serum calcium and serum albumin levels are estimated (estimation of the concentration of ionized calcium). but a direct determination of ionized calcium is due to the technical difficulties in measuring normally only patients in whom significant abnormalities are suspected in the protein binding of serum calcium reserved. The normal ionized serum calcium concentration range varies somewhat between laboratories but is generally 4.7 to 5.2 mg / dL (1.17 to 1.30 mmol / l). Regulation of calcium metabolism The metabolism of calcium and phosphate (overview of disorders of phosphate concentration) is very strong interdependent. The regulation of both the calcium and the phosphate balance is largely determined by the levels of circulating PTH, vitamin D and to a lesser extent also by calcitonin. The concentrations of calcium and phosphate are also by their ability to chemically bond to calcium phosphate, in a certain dependency on each other. The product of the concentrations of calcium and phosphate (in mEq / l) is estimated under normal conditions, to about 60; If this product exceeds 70, the precipitation of calcium phosphate crystals in the soft tissue becomes possible. Calcification of vascular tissue accelerated atherosclerotic vascular disease and may occur when the calcium and phosphate product is even lower (> 55), especially in patients with chronic kidney disease. PTH is formed by the four parathyroid glands, the parathyroid glands. It has various functions; the most important thing is to prevent hypocalcemia. The cells of the parathyroid seen a decrease in serum calcium and with secretion of preformed PTH in the circulation. PTH increases the serum calcium within minutes by an increase in renal and intestinal calcium absorption and a rapid mobilization of calcium and phosphate from the bones (bone resorption). The urinary calcium excretion usually runs parallel to the sodium excretion and is affected by many of the factors that regulate sodium transport in the distal tubules. Nevertheless, PTH enhances calcium reabsorption in the distal tubules independent of sodium. PTH also lowers the renal Phosphatreabsorption and thus increases renal phosphate excretion. Renal phosphate excretion prevents the solubility product of calcium and phosphate is exceeded when rise in response to PTH secretion, the plasma calcium concentrations. PTH increases the serum calcium and indirectly by stimulating the conversion of vitamin D into its active form, calcitriol. This form of vitamin D increases the absorption of calcium from the intestine. Despite the increased calcium absorption, a long-term excessive increase in PTH secretion through the inhibition of osteoblast function and the increase in osteoclast activity to increased bone resorption. Both PTH and vitamin D are important regulators of bone growth and bone remodeling (vitamin D deficiency and dependence). A radioimmunoassay to the intact PTH molecule remains the recommended method to test for PTH. the second generation intact PTH assays are available. These tests measure bioavailable PTH or total PTH. They result values ??corresponding to 50-60% of the values ??obtained with the older assay. Both assays can be used as a result of kidney disease for the diagnosis of primary hyperparathyroidism or to monitor a hyperparathyroidism, as long as the normal ranges are noted. PTH increases urinary cAMP. Occasionally, the total or nephrogenic cAMP excretion of diagnosing a pseudohypoparathyroidism is determined. Calcitoninwird by thyroid parafollicular cells (C-cells) secreted. Calcitonin lowers serum calcium levels by increasing the cellular uptake, renal excretion and bone formation. The effects of calcitonin on bone metabolism are much weaker than that of PTH or vitamin D.