After swallowing an aspirin tablet, it will go on a journey through your digestive system. absorption The tablet will travel down the esophagus into the stomach where it is dissolved into much smaller particles, these particles will continue their journey into the small intestine where most of them will be absorbed into the blood. The small intestine wall, also called lumen are lined with tiny villi which stick out to provide a large surface area for the nutrients inside the food to be absorbed. Looking closer at these villi, you can see they have a rich blood supply and are covered in a thin layer of epithelial cells. The aspirin molecules will work at their way through epithelial cells and entered into the bloodstream where they are carried around the body. Distribution Blood plasma contains complex molecules called albumin, albumin is a protein made by the liver which transports nutrients around the body. Albumin also binds to drugs that enter the bloodstream. Here you can see some of the aspirin molecules binding to the albumin, all the aspirin particles that have been bound will be filtered out as pass through the liver and only the remaining molecules will get through and have any effect on the body. Different drugs will bind to albumin in different amounts depending on their affinity for plasma protein. The next stop on the journey is liver, the aspirin rich in blood will enter the liver through the hepatic portal vein at bottom, and it will exit at the top via the hepatic vein. At this stage, even more of the aspirin will be removed through a process called first pass metabolism. The liver job is a bit like a filter, it will metabolize drugs before they reach the rest of the body, it does this in a few steps. Phase 1 metabolism, first aspirin is hydrolyzed breaking off acetic acid and leaving behind salicylic acid, this salicylic acid isn't water-soluble, so it can't be excreted in urine yet. Phase 2 metabolism, an ionized group is then added to the salicylic acid, forming glucuronide which is water-soluble and can be excreted in urine, a lot less of the aspirin will continue its journey onto the rest of the body including the site of the pain, only 68% of orally taking aspirin will have any effect at all because of all the filtering that the body has done. This percentage is called the drugs oral bioavailability, if drugs are not administered orally eg intravenously or bucoly, then they can bypass the small intestine and liver, so none of this process takes place and they are 100% bioavailability, we are now at site of some skin tissue damage, tissues in the skin are creating prostaglandins which are causing inflammation, the prostaglandins are sending message to nerves in the skin responsible for the sensation of pain. Once aspirin arrives in the blood supply at the site, it prevents the production of prostaglandins in the tissue which will reduce the swelling and stop the message being sent to the nerves that precedes the pain. Excretion Any remaining aspirin in the blood will go round and round the blood supply going back through the several times until it is all used up or filtered out of the body, it traveled into the kidneys and then into the bladder for excretion. |
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