Calcium - the element

Calcium is an essential nutrient in our diet.   Adults require some 1000 – 1200 mg of calcium per day.  After carbon, hydrogen, oxygen and nitrogen, calcium is the most abundant element in the body.  Most of this calcium is in the teeth and the skeleton, where it is combined with phosphate to form a compound known as apatite.    In young people, a diet poor in calcium (or Vitamin D) can lead to rickets, where the bones soften, sometimes leading to fractures and deformity. If there is not enough Vitamin D in the diet or manufactured by the skin, calcium may not be absorbed properly by the gut.   In adults, long-term calcium deficiency can lead to osteoporosis, where the bone ‘thins’, making fractures more likely.   Foods rich in calcium include milk and most dairy products, soy milk, various nuts and fish (e.g. sardines and whitebait ), almonds & tofu. 

Building of the skeleton and teeth is not the only job that calcium has in the body.  It has a vital role in blood clotting and muscle contraction.  The blood needs to be able to clot so that it is not continuously lost at a cut or wound, but equally it must not clot too freely; if it does, then a blood clot may form within a blood vessel leading to a heart attack (if it blocks off a coronary artery) or a stroke (if it stops the blood flow to parts of the brain). 

At a cut or wound, small blood cells – platelets or thrombocytes – are activated to produce an enzyme, thrombokinase.  This acts on another blood protein called prothrombin, but it needs calcium ions (Ca2+) to convert it into thrombin.  The thrombin, in turn, acts on fibrinogen (produced in the liver) a soluble protein in the blood.  The soluble fibrinogen is converted into (threads of) insoluble fibrin.  The microscopic threads of fibrin help trap blood cells to form a clot, which will harden to form a scab – sealing off the cut, preventing the loss of blood and the entry of micro-organisms.  The processes involved in blood clotting are very complex. Styptic pencils (which contain aluminium compounds – Al3+) can help staunch the flow of blood at minor cuts.

Calcium is also involved in the process of muscle contraction.  For a muscle to contract, a small electrical signal (an impulse) is sent from the brain down a nerve to the surface of a muscle, here it causes the release of a neurotransmitter molecule.  There is then a change in the electrical state of the surface of the muscle cell.  A special membrane system, known as the sarcoplasmic reticulum, releases calcium ions (Ca2+) which cause the muscle proteins to move relative to each other – causing contraction.

Calcium is also a vital nutrient in plants.  It is important in the formation of the cellulose cell walls, which surround the living protoplasts of plant cells.  It forms part of the molecule of calcium pectate, which acts as a cement or glue, helping to stick / hold cells together.  It is also involved in cell membranes and the activation of certain enzymes.  If a plant is deficient in calcium, it is usually young leaves or developing flowers and fruits that are affected, giving rise to conditions such as ‘tip burn’.

Comments on this article

bob 22 April, 2010

Good to know.
Thank you

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