The intracellular concentration of calcium in the cytosol of unstimulated cells is around 0.1 μmol/L, which is less than 1/20,000 of that in extracellular fluid. Intracellular calcium has key roles in many important physiologic functions, including muscle contraction, hormone secretion, glycogen metabolism, and cell division. Physiologically, calcium may be classified as intracellular or extracellular.
OVERALL CHARGE OF CALCIUM FREE
Calcium can be redistributed among the three plasma pools, acutely or chronically, by alterations in the concentrations of protein and small anions, changes in pH, or changes in the quantities of free calcium and total calcium in the plasma.
In vitro, for each 0.1-unit change in pH, approximately 0.2 mg/dL (0.05 mmol/L) of inverse change occurs in the serum-free calcium concentration. Alkalosis leads to an increase in the negative charge of proteins, increasing binding, resulting in a decrease in free calcium conversely, acidosis leads to a decrease in negative charge, decreasing binding and resulting in an increase in free calcium. Because calcium binds to negatively charged sites on proteins, its binding is pH-dependent. The free calcium fraction is the biologically active form. Ībout 50% of the calcium present in circulation is free (also known as ionized calcium) 40% of serum calcium is bound to proteins, especially albumin (80%) and, secondary, to globulins (20%) and about 10% exists as various small diffusible inorganic and organic anions (e.g., bicarbonate, lactate, citrate). In blood, virtually all calcium is present in the plasma. Soft tissues and extracellular fluid contain about 1% of the body’s calcium. The skeleton contains approximately 99% of the body’s calcium, predominantly as extracellular crystals of an unknown structure and a composition approaching that of hydroxyapatite. An average human body (70 kg) contains about 1 kg, or approximately 25 mol, of calcium. Ĭalcium is the fifth most common element in the body and the most prevalent cation. An interprofessional team is essential for proper patient management. Laboratory error can cause inaccurately reported calcium levels, and preventive measures should be included in specimen collection and analysis. Calcium derangements can result from many diseases or therapies that affect hormone secretion, receptor sensitivities, intestinal absorption, and renal effectiveness. Calcium can also be analyzed in the urine by calcium concentration, urine calcium to creatinine ratio (UCa:UCr), or fractional excretion of calcium (FeCa). Total calcium values should be corrected for current albumin concentrations, which act as a carrier protein and can affect the reported results. Serum calcium can be measured by a venous sample, with physiologic levels ranging from 8.8 mg/dl to 10.4 mg/dL for total calcium and 4.7 mg/dL to 5.2 mg/dL for ionized calcium. Calcium must be ingested endogenously, and absorption in the gastrointestinal system is influenced by hormones PTH and calcitriol (1,25-dihydroxy vitamin D). Calcium is tightly regulated by the parathyroid hormone (PTH), calcitonin, and calcitriol, which regulate serum calcium levels. It is an essential element for proper cardiac function, the structural integrity of bone, and muscular contraction and acts as an enzymatic signal in biochemical pathways. Calcium is a prominent molecule involved in many biochemical processes throughout the body.
0 kommentar(er)
