Calcium plays a vital role in the biochemistry of the cell, particularly in signal transduction pathways. The skeleton acts as a major storage site for the element and releases Ca²⁺ into the bloodstream under controlled conditions. Circulating calcium is either in the free, ionized form or bound to blood proteins such as albumin. The hormone secreted by the parathyroid gland, parathyroid hormone, regulates the resorption of Ca²⁺ from bone.

Organs and tissues

Different tissues contain Ca in diffent concentrations. In vertebrates Ca (in a form of CaSO₄) is the most important (and specific) element of bones.

Some invertebrates use Ca for building their outer (radiolaria) or inner skeleton.

There are also some plants which accumulate Ca in their tissues, thus making them more firm.

Cell biology

In cell biology Ca²⁺ ions are one of the widespread messengers, their entrance into cytoplasm (either from outside the cell through the cell membrane via calcium channels, or from some internal Ca storages) represent the most important signal for the whole cell machinery. Ca²⁺ entering the cell causes the specific action of this cell, whatever this action is: secretory cells release vesicles with their secretion, muscle cells contract, synapses go into processes of synaptic plasticity etc.

Calcium's function in muscle contraction was found as early as 1882 by Ringer and led the way for further investigations to reveal its role as a messenger about a century later. Because its action is interconnected with cAMP, they are called synarchic messengers. Calcium can bind to several different calcium-modulated proteins such as troponin-C (the first one to be identified) or calmodulin.

The same Ca²⁺ ions can, however, bring damage to cells if there are too many of them (for example in a case of overexcitation in neural circuits ). This may even cause cell apoptosis. One cause of hypercalcemia is hyperparathyroidism.

Food sources

Calcium amount in foods, 100g:

• vaccine = 116 mg
• human milk = 33 mg
• milk powder = 909 mg
• parmesan (cheese) = 1140 mg
• ricotta (skimmed milk cheese) = 90 mg
• egg, 1 = 54 mg
• molasses = 273 mg
• brown sugar = 85 mg
• white sugar = 0 mg
• honey = 5 mg
• flour = 41 mg
• wheat germ = 72 mg
• beef = 12 mg
• horse meat = 10 mg
• cod = 11 mg
• trout = 19 mg
• hazels = 250 mg
• almonds = 234 mg
• nuts = 99 mg
• lentils = 79 mg

See also: Ca-binding proteins

External links

• http://www.parrottalk.com/calcium.html Calcium Rich Vegetables
• http://www.vitalityquest.ca/page42.html
• http://www.nof.org/prevention/calcium.htm Calcium and vitamin D.