99% of the body's calcium is contained within the skeleton as calcium salts making up the inorganic parts of the bone. The remaining 1% is found in several forms in the blood. The blood calcium levels are tightly controlled within a very narrow range of 2.1-2.6 millimoles per litre. The reason for this is that the movement of calcium ions across cell membranes affects many fundamental processes such as:
Tiny alterations of blood calcium levels upset this delicate balance of calcium movement and can lead to a wide range of problems.
When excess blood calcium accumulates the following can occur:
1. The formation of stones - the excess calcium can form stones (calculi) in organs such as the kidneys.
2. Fractures - hypercalcaemia often indicates excessive resorption (degradation) of bones making them prone to break after only minor trauma (pathological fractures).
3. Proximal myopathy - weakness in the proximal muscles (the muscles of the upper limbs) due to insufficient calcium for efficient muscle contraction.
4. Pancreatitis - calcium deposits in the pancreas can result in inflammation of the pancreas causing pain, nausea and vomiting.
5. Mental changes - alterations in brain activity due to abnormal nerve function can lead to depression, confusion, memory loss and parkinsonism-type symptoms..
When blood calcium becomes too low the following can occur:
1. Paraesthesia - this is a sensation of numbness in areas of the body and is due to impaired activity of sensory nerves.
2. Cramps - altered calcium levels cause abnormalities of muscle contraction resulting in cramps around the body. In particular it can cause laryngospasm, (spasm of the muscles of the larynx).
3. Tetany - this is prolonged sustained involuntary contraction of muscles due to muscle nerve conduction problems.
4. Agitation and seizures - abnormal levels of brain activity can cause seizures and agitation.