The main feature of arthritis is inflammation, which is a reaction of the joint tissues to some form of injury or damage. The consequences of this kind of reaction were know even in ancient times. Celsus, a Roman Physician of the first century AD, listed 4 major signs of inflammation: heat, pain, redness and swelling (the Latin names being color, dolor, rubor and tumor). A 5th sign, lost of function (functio laesa), is sometimes added. Although the description refers to inflammation is general, it still holds true to joint inflammation and reflects, remarkably accurately, the symptoms experienced by those afflicted with arthritis. In addition, there, may be a slight rise in body temperature, headache, loss of appetite and general feeling of ill-health.
We now know that the changes in the body responsible for these symptoms are fairly complex. In simple terms, they consist of widening of the blood vessels in the synovial membrane with an increase of blood sent by the body to the affected joint. The blood vessel walls then leak proteins and fluids, which make up part of the blood, into the surrounding tissues. Another characteristics change is the white blood cells ( leucocytes) travelling through these blood vessels. This swelling of the blood vessels and accumulation of fluid in the inflamed tissues explains the redness, warmth and swelling first observed by Celsus. Pain comes from the irritation of the specialized nerve endings within the joint, through how this happens is not really known. Much research has been undertaken in arthritis to find out what really, triggers off inflammation. This has revealed that a large number of chemical substances, naturally present in the human body, take part.
If the injury or damage to the joint is temporary or not too severe, the acute inflammation ( or synovitis) subsides and repairing by the body begins. Blood vessels return to their original size, normal blood flow is established, the white blood cells either die or re- enter the blood vessels, tissues fluid is absorbed into the circulation and injured cells are replaced. If, on the other hand, the reason for the inflammation carry on, the arthritis become lasting, or chronic. The symptoms and signs described above are less dramatic, but they are disabling nonetheless. Healing is only partial, occuring side by side with 'grumbling' inflammation. The main feature of this chronic inflammation is the infiltration of the membrane lining the joint by various types of cells - scavenger and repair cells, large and small. The body fails to eliminate the foreign invader and become a little confused, some of these cells being responsible for the inflammation remaining.
Recent research has thrown light on the way in which some of these cells are involved in damage to the joints. Normally, the body can tell what is 'self' and what is 'foreign': this is called the bodys 'immune' system. In certain situations, this system becomes defective and the bodys defense cells produce antibodies ( substance which the human body makes to destroy disease-making 'invaders') against itself, so much so that they cause tissue injury. A vicious circle is set up, with inflammation producing damage, which makes the body produce antibodies which produce yet more inflammation and mischief!
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