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For us or against us? - The immune system as a cause of disease

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Introduction

FOR US OR AGAINST US? - THE IMMUNE SYSTEM AS A CAUSE OF DISEASE The immune system is equipped with a network of cells and tissues which enables the body to create a defence mechanism against invading organisms. It has evolved as a system poised to initiate and maintain protective responses against any harmful foreign element the body may encounter.9The cells in the immune system have the ability to distinguish between self or invader cells, and they try to get rid of invaders. However this system is not without flaws, autoimmune diseases are the result of specific immune responses directed against structures of the self .This happens as a result of the activation of B or T lymphocytes reacting against antigens of the body's own tissues. Myasthenia gravis is an example of a chronic autoimmune disease which affects the neuromuscular junction. Since muscle contraction depends on effective neuromuscular transmission between the nerves and muscles any interruption may lead to partial or complete paralysis. Weakness increases during periods of activity and improves after periods of rest. Certain muscles such as those that control eye and eyelid movement, facial expression, chewing, talking and swallowing are often involved in this disorder. The disease affects individuals of any age but the peak prevalence is amongst women in their twenties and men in their fifties and sixties.3 FIGURE 1 The immune system is composed of many cells; of these the white blood cells form the backbone. ...read more.

Middle

Acetylcholine is a chemical messenger which is secreted at the ends of certain fibres; it transmits messages in the form of excitatory signals across the junction. FIGURE 3 The neuromuscular junction sending a signal When a neurone is not sending a signal, its inside is negative relative to the outside .This is due to the imbalance of sodium and potassium ions. The action potential is an explosion of electrical activity that is created by a depolarising current. When an action potential reaches the presynaptic membrane of the neurone, it causes calcium ions to diffuse in. The calcium ions cause vesicles containing acetylcholine to fuse with the presynaptic membrane releasing its contents into the synaptic cleft. The acetylcholine then diffuses across the cleft and binds to specific recognition site of receptors in the postsynaptic membrane. This results in opening of receptor operated ion channels, allowing pulses of inward ionic current (mainly Na+) to flow; this results in depolarisation. If enough depolarisations are produced frequently enough, a muscle action potential and contraction results. In muscle a single impulse usually causes enough depolarization to reach threshold. The muscle action potential causes release of (Ca2+) from the sarcoplasmic reticulum of the muscle and this triggers muscle contraction .Acetylcholine diffuses away from its receptor site, the ion channel then closes. ...read more.

Conclusion

This however may manifest itself as an autoimmune disease an example of which is myasthenia gravis. Another explanation is that in molecular mimicry the immune system may mistake portions of the acetylcholine receptor for portions of an invading virus; this is because some pathogens have similar structure to that of the host tissues. No candidate virus has yet been identified; this plays an important role in the immune response to infection in autoimmune diseases. Hence an infection may trigger the occurrence of the disease in some cases. Recent research has also shown that genes controlling other parts of the immune system, called MHC genes, appear to influence how susceptible a person is to developing autoimmune disease. However this like all other explanations of the disease is not a proven fact. In short the immune system works for us but it could also turn against us. The exact reason why it turns against us is not known. However recent research proposes that the thymus gland is the most logical cause. The future looks very bright for sufferers of the disease because what used to be a grave muscle disease is no longer so. With recent research and technology mortality rate is essentially zero, this is due to optimal care and the different methods of treatments currently available. Despite these impressive advances, it is still not known the origin and the factors that contribute to this chronic disease. ...read more.

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