Background
When you suffer from a headache, fever, arthritis, injury or other disorder that causes pain or inflammation, your body produces hormone-like chemicals called prostaglandins. Prostaglandins send an alert message to the brain that pain or a threat of injury is occurring somewhere in the body. This is how you become aware of your pain.
Prostaglandins set in motion a series of reactions that may result in a raised temperature to fight infection or a release of fluids from body cells. These fluids cause swelling and inflammation in the affected area. This is your body's way of trying to protect the injured area by providing a liquid cushion against further damage.
Normally, at the first sign of pain or injury, your body produces cyclooxygenase (COX) enzymes that synthesize prostaglandins from arachadonic acids, which are fatty acids that come from polyunsaturated fats (vegetable oils) in your diet. There are two types of COX enzymes: COX-1 and COX-2. COX-1 enzymes are involved in the production of prostaglandins that serve normal day-to-day functions in the body, such as protecting the lining of the stomach and helping blood to form clots. COX-2 enzymes are involved in the production of prostaglandins when pain and inflammation occur.
Action
Aspirin works by inhibiting the action of COX-1 and COX-2 enzymes, which prevents the conversion of arachadonic acid to prostaglandins. To accomplish this, aspirin blocks a tunnel-like molecular structure through which arachadonic acid flows, so the acid cannot reach its destination and be converted into prostaglandins.
Aspirin also attaches itself to COX-2 enzymes. Once aspirin is attached, it changes the chemical structure of the enzyme so that it no longer functions normally. Without this enzyme, prostaglandins cannot be produced.
Results
When you take aspirin, the messages normally sent to the brain about pain and injury are discontinued. When your brain is unaware of an injury or cellular disturbance, you don't feel the pain of a headache or body ache. Fever is reduced, and at the same time, the amount of fluids released by body cells is reduced, so inflammation and swelling subside.
Aspirin prevents the formation of clots in the bloodstream by preventing the synthesis of prostaglandins in the blood. The result is reduced risk of blocked arteries, heart attack and ischemic stroke.
Since aspirin inhibits both COX-1 and COX-2 enzymes, the production of both ordinary prostaglandins and those that react to distress is reduced. This cuts back on prostaglandins needed for everyday purposes, such as protecting the lining of the stomach and causing blood to clot when necessary and that is why side effects occur. Normal to high doses of aspirin can cause bleeding in the stomach, for instance, and very high doses can be toxic.
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