Calcium biological roles

Complexes of alkali metals and alkaline-earth metals with carbohydrates have been reviewed in this Series,134 and the interaction of alkaline-earth metals with maltose has been described.135 Standard procedures for the preparation of adducts of D-glucose and maltose with the hydroxides of barium, calcium, and strontium have been established. The medium most suitable for the preparation of the adduct was found to be 80% methanol. It is of interest that the composition of the adducts, from D-glucose, maltose, sucrose, and a,a-trehalose was the same, namely, 1 1, in all cases. The value of such complex-forming reactions in the recovery of metals from industrial wastes has been recognized. Metal hydroxide-sugar complexes may also play an important biological role in the transport of metal hydroxides across cell membranes. 

CALCIUM (In Biological Systems). The biological role and. consequently. the importance of calcium in foods for humans and feedstuffs for... 

Biological Role of Calcium. Calcium represents a large weight fraction of the elemental composition of the human body. Of the 1.3 kg of... 

The exact biological role of calcitonin remains elusive. Neither deficiency nor excess seems to produce pathological changes. Calcitonin may prevent hypercalcemia during childhood when calcium intake is high, or it may be important in adults during periods of hypercalcemia or high calcium intake. 

The T-type or low-voltage-activated calcium channels have been identified in a variety of smooth muscle cells. They activate at low membrane potentials (around -50 mV) with a maximum around -20 mV, have a small conductance (7-8 pS with 110 mM Ba2+ as charge carrier), inactivate rapidly, and are blocked by 10-100 xM Ni2+ and a variety of compounds, including some of the organic calcium channel blockers. The biological role of the T-type channels remains to be established owing to the lack of specific blockers. 

In addition to its important biological role, calcium metal is widely used in various industrial processes, for example in metallurgy. Calcium salts (carbonate, sulfate, phosphate, chloride, nitrate) are components of building stones, calcined gypsum, fertilizers and form the basis for many other technically useful substances. 

Demple B, Sung JS (2005) Molecular and biological roles of Apel protein in mammalian base excision repair. DNA Repair (Amst) 4 1442-1449 Dienel GA (1984) Regional accumulation of calcium in postischemic rat brain. J Neurochem 43 913-925... 

Barium is a non essential element for humans, and has no biological role. It is an abundant element and humans take about 1 mg per day through foods (carrots, onions, lettuce and oranges). Barium is similar to calcium and is absorbed easily, but it does not have any known useful purpose and function in the body. 

The teeth of the limpet P. vulgata were shown to consist of 80 nm fibers rich in SiOs probably bonded together by FejOj (67). In the sea cucumber (Molpadia, intermedia, Holothurioidea) it is interesting that silica occurs in granules in the skin in the form of spheres 100-190 nm in diameter mixed with spherical particles of ferritin of the same size. The latter is a calcium-magnesium-basic iron phosphate (68). The biological role of the silica is unknown, but since the ferritin may serve as... 

Although it is being found that vitamin D metaboUtes play a role ia many different biological functions, metaboHsm primarily occurs to maintain the calcium homeostasis of the body. When calcium semm levels fall below the normal range, 1 a,25-dihydroxy-vitainin is made when calcium levels are at or above this level, 24,25-dihydroxycholecalciferol is made, and 1 a-hydroxylase activity is discontiaued. The calcium homeostasis mechanism iavolves a hypocalcemic stimulus, which iaduces the secretion of parathyroid hormone. This causes phosphate diuresis ia the kidney, which stimulates the 1 a-hydroxylase activity and causes the hydroxylation of 25-hydroxy-vitamin D to 1 a,25-dihydroxycholecalciferol. Parathyroid hormone and 1,25-dihydroxycholecalciferol act at the bone site cooperatively to stimulate calcium mobilization from the bone (see Hormones). Calcium blood levels are also iafluenced by the effects of the metaboUte on intestinal absorption and renal resorption. 

Interaction of vitamin D and its metaboUtes with sex hormones has been demonstrated, particularly ia birds ia which the egg-laying functions combine calcium needs and reproductive activity. The metaboUtes of vitamin D behave as hormones. As such, they play an active role ia the endocrine system, along with other hormones, to maintain the various body functions. Several biological influences of metaboUtes of vitamin D have been studied, including effects related to cancer (193—197), skin diseases (198—201), immunomodulatory effects (202,203), and Alzheimer s disease (204—206) (Fig. 9). 

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