Albumin calcium bound

About 40% of serum calcium is protein bound, with most of it 80%) being bound to albumin. Generally, one or two calcium ions are associated with serum albumin. Albumin serves as a calcium buffer. Jt can bind more calcium ions when excessive concentrations of calcium appear in the bloodstream. About 13% of the calcium in scrum is weakly complexed with phosphate, citrate, and sulfate. About half (47%) of serum calcium occurs as the free calcium ion. The level of free scrum Ca is maintained within narrow limits, 1.0 to 1.25 mM (40 to 50 pg/mJ). The normal concentration of total serum calcium (bound plus free) is 85 to 105 pg/ml. Conditions in which the level of free serum calcium fails below and rises above the normal range are called hypocalcemia and hypercalcemia, respectively. The term ionized calcium is often used to refer to the concentrations of free calcium. This term is not scientifically accurate, because all of the calcium in the body is ionized. Calcium does not engage in the formation of covalent bonds (Cotton and Wilkinson, 1966). 

Three forms of calcium are in equilibrium in serum nondiffusible calcium bound primarily to albumin diffusible complexes of calcium with lactate, bicarbonate, phosphate, sulfate, citrate, and other anions and diffusible ionized calcium (Ca " ). Ionized calcium accounts for approximately half of total serum calcium, and nondiffusible and complexed calcium account for 45% and 5%, respectively. Ionized calcium is the physiological active form its concentration is regulated by the parathyroid gland. A decrease in serum ionized calcium can cause tetany (involuntary muscle contraction) and related neurological symptoms, regardless of the total serum calcium concentration. 

Approximately 35% of the serum calcium is bound to protein. Serum albumins are twice as effective (10.5 moles of calcium bound to 10 grams) as globulins (5.6 moles of calcium bound to 10 grams) in the chelating calcium. 

Another important function of albumin is its ability to bind various ligands. These include free fatty acids (FFA), calcium, certain steroid hormones, bilirubin, and some of the plasma tryptophan. In addition, albumin appears to play an important role in transport of copper in the human body (see below). A vatiety of drugs, including sulfonamides, penicilhn G, dicumarol, and aspirin, are bound to albumin this finding has important pharmacologic implications. 

More than 99% of total body calcium is found in bone the remaining less than 1% is in the ECF and ICE Calcium plays a critical role in the transmission of nerve impulses, skeletal muscle contraction, myocardial contractions, maintenance of normal cellular permeability, and the formation of bones and teeth. There is a reciprocal relationship between the serum calcium concentration (normally 8.6 to 10.2 mg/dL [2.15 to 2.55 mmol/L]) and the serum phosphate concentration that is regulated by a complex interaction between parathyroid hormone, vitamin D, and calcitonin. About one-half of the serum calcium is bound to plasma proteins the other half is free ionized calcium. Given that the serum calcium has significant protein binding, the serum calcium concentration must be corrected in patients who have low albumin concentrations (the major serum protein). The most commonly used formula adds 0.8 mg/dL (0.2 mmol/L) of calcium for each gram of albumin deficiency as follows ... 

For acute symptomatic hypocalcemia, 200 to 300 mg of elemental calcium is administered IV and repeated until symptoms are fully controlled. This is achieved by infusing 1 g of calcium chloride or 2 to 3 grams of calcium at a rate no faster than 30 to 60 mg of elemental calcium per minute. More rapid administration is associated with hypotension, bradycardia, or cardiac asystole. Total calcium concentration is commonly monitored in critically ill patients. Under normal circumstances, about half of calcium is loosely bound to serum proteins while the other half is free. Total calcium concentration measures bound and free calcium. Ionized calcium measures free calcium only. Under usual circumstances, a normal calcium level implies a normal free ionized calcium level. Ionized calcium should be obtained in patients with comorbid conditions that would lead to inconsistency between total calcium and free serum calcium (abnormal albumin, protein, or immunoglobulin concentrations). For chronic asymptomatic hypocalcemia, oral calcium supplements are given at doses of 2 to 4 g/day of elemental calcium. Many patients with calcium deficiency have concurrent vitamin D deficiency that must also be corrected in order to restore calcium homeostasis.2,37,38... 

Around 99% of calcium is contained in the bones, whereas the other 1% resides in the extracellular fluid. Of this extracellular calcium, approximately 40% is bound to albumin, and the remainder is in the ionized, physiologically active form. Normal calcium levels are maintained by three primary factors parathyroid hormone, 1,25-dihydroxyvitamin D, and calcitonin. Parathyroid hormone increases renal tubular calcium resorption and promotes bone resorption. The active form of vitamin D, 1,25-dihydroxyvitamin D, regulates absorption of calcium from the GI tract. Calcitonin serves as an inhibitory factor by suppressing osteoclast activity and stimulating calcium deposition into the bones. 

ECF calcium is moderately bound to plasma proteins (46%), primarily albumin. Unbound or ionized calcium is the physiologically active form. 

Once in the serum, aluminium can be transported bound to transferrin, and also to albumin and low-molecular ligands such as citrate. However, the transferrrin-aluminium complex will be able to enter cells via the transferrin-transferrin-receptor pathway (see Chapter 8). Within the acidic environment of the endosome, we assume that aluminium would be released from transferrin, but how it exits from this compartment remains unknown. Once in the cytosol of the cell, aluminium is unlikely to be readily incorporated into the iron storage protein ferritin, since this requires redox cycling between Fe2+ and Fe3+ (see Chapter 19). Studies of the subcellular distribution of aluminium in various cell lines and animal models have shown that the majority accumulates in the mitochondria, where it can interfere with calcium homeostasis. Once in the circulation, there seems little doubt that aluminium can cross the blood-brain barrier. 

Second, albumin is a non-specific carrier protein. A wide range of chemically disparate compounds are bound loosely to albumin for transport through the blood stream. Important examples include calcium, bilirubin, drugs and free fatty acids. 

Of the plasma total concentration of calcium (around 2.5 mmol/1), approximately half is bound to albumin. The unbound fraction is physiologically active in roles such as clotting, in regulating neuromuscular membrane potential and of course for bone formation. There exists an equilibrium between the bound and free fractions, so the albumin can be seen as a buffer able to release or take up calcium as circumstances... 

Serum calcium or serum ionized calcium concentrations (ionized calcium concentrations are preferable to determine free and bound calcium, especially with concurrent low serum albumin)... 

Calcium is present in three forms e.g., as free calcium ion, bound to plasma protein albumin and in diffusable complexes. The endocrine system, through parathyroid hormone and calcitonin, helps in keeping the concentration of ionized plasma calcium in normal level. Decrease in plasma levels of ionized calcium leads to increased parathyroid hormone secretion. Parathyroid hormone tends to increase plasma calcium level by increasing bone resorption, increasing intestinal absorption and increasing reabsorption of calcium in kidney. Vitamin D acts by stimulating... 

The important bacterial storage material poly-hydroxybutyric acid is related metabolically and structurally to the lipids. This highly reduced polymer is made up of D-(3-hydroxybutyric acid units in ester linkage, about 1500 residues being present per chain. The structure is that of a compact right-handed coil with a twofold screw axis and a pitch of 0.60 nm.a Within bacteria it often occurs in thin lamellae 5.0 nm thick. Since a chain of 1500 residues stretches to 440 nm, there must be 88 folds in a single chain. Present in both cytoplasmic granules and in membranes,b polyhydroxybutyrate can account for as much as 50% of the total carbon of some bacterial In E. coli and many other bacteria polyhydroxybutyrate is present in a lower molecular mass form bound to calcium polyphosphates, proteins, or other macromolecules.d e It has also been extracted from bovine serum albumin and may be ubiquitous in both eukaryotes and prokaryotes.d/e The polymer may function in formation of Ca2+ channels in membranes.b/d... 

Hypoproteinemia may result in low levels of serum calcium, ceruloplasmin, and transferrin. Because losses of iron are at most 0.5-1.0 mg/24 hr, even with the heaviest proteinuria, other factors must operate to produce iron deficiency and microcytic hypochromic anemia. Although the copper-binding protein ceruloplasmin is lost in the urine in nephrotic subjects and its plasma levels are low, plasma and red cell copper concentrations are usually normal. Zinc circulates mainly bound to albumin and also to transferrin, and thus the reported reduction zinc concentration in plasma, hair, and white cells in nephrotic patients is not surprising. 

Q7 The total serum calcium concentration is normally about 9.5 mg dl 1. Approximately half of this is bound to plasma protein, mostly to albumin. Most of the remainder is unbound or ionized calcium, which is the physiologically and clinically important form. Hypercalcaemia, normally defined as a serum concentration of >12 mgdl-1, may sometimes be caused by excessive consumption of calcium in the diet. More important pathologically is malignant disease. Hypercalcaemia occurs when there are bone metastases associated with breast or prostate cancer. However, many tumours can produce a PTH-like protein causing elevated serum calcium levels. Furthermore, intoxication and immobilization of vitamin D or excess vitamin D may also cause hypercalcaemia. 

Calcium is the most abundant mineral in the body, about 1 kg, 99% of which is found in the skeleton in the form of calcium phosphate salts. There is a significant exchange of calcium between the bone and extracellular fluid (ECF) serum levels of calcium are tightly regulated (it can vary with the level of serum albumin, to which calcium is bound). 

ECF calcium is moderately bound to plasma proteins (46%), primarily albumin. Unbound or ionized calcium is the physiologically active form. Each 1 g/dL drop in serum albumin concentration below 4 g/dL decreases total serum calcium concentration by 0.8 mg/dL. 

Approximately 50% of the total calcium in plasma is either bound to albumin or complexed to small ligands. The remaining ionized fraction is the biologically active form. Whenever... 

Protein bound This is calcium that is bound to albumin. 

With prolonged bed rest, fluid retention occurs and plasma protein and albumin concentrations may be decreased by an average of 0.5 and 0.3g/dL, respectively. The concentrations of protein-bound constituents are also reduced, although mobilization of calcium from bones with an increased free ionized fraction compensates for the reduced protein-bound calcium, so serum total calcium is less affected. Serum aspartate aminotransferase activity is usually slightly less in individuals confined to bed than in those undertaking normal physical activity. Initially and paradoxically, creatine kinase (CK) activity is increased as a result of its release from skeletal muscles, but ultimately, CK activity may be less than in active, healthy individuals. Serum potassium may be reduced by up to 0.5mmol/L because of reduction of skeletal muscle mass. 

Low total serum calcium (hypocalcemia) may be due to either a reduction in the albumin-bound calcium, the free firaction of calcium, or both (Box 49-Hypoalbu-minemia is the most common cause of pseudohypocalcemia (decreased total and norma free calcium) because 1 g/dL of albumin binds approximately 0.8 mg/dL of calcium. Common clinical conditions associated with low serum... 

The binding of calcium by protein and small anions is influenced by pH in vitro and in vivo. Albumin, with up to 30 binding sites for calcium,accounts for approximately 80% of the protein-bound calcium. Increasing the pH of a specimen in vitro increases the ionization and negative charge on albumin and other proteins, leading to an increase... 

Changes in posture cause fluid shifts within 10 minutes and thus alter the concentration of cells and large molecules, including albumin and total calcium (as part of it is protein-bound) in the vascular compartment. Standing decreases intravascular water and increases the total calcium concentration by 0.2 to 0.8 mg/dL (0,05 to 0.20 mmol/L), whereas... 

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