Aspirin Journey through the body

Journey of Aspirin through the Digestive System

Absorption

• The aspirin tablet undergoes a journey through the digestive system after swallowing.

• It travels down the oesophagus into the stomach, where it is dissolved into smaller particles.

• The dissolved particles continue their journey into the small intestine, where most are absorbed into the blood.

• The walls of the small intestine, also known as the lumen, are lined with tiny structures called villi that increase surface area for nutrient absorption.

Structure of Villi

• Villi are equipped with a rich blood supply.

• They are covered by a thin layer of epithelial cells.

• Aspirin molecules pass through these epithelial cells to enter the bloodstream, allowing for systemic distribution.

Distribution

• The blood plasma contains albumin, a protein synthesized by the liver, which transports nutrients throughout the body.

• Albumin also binds to drugs, including aspirin molecules.

• Bound aspirin particles are filtered out as blood passes through the liver, while unbound aspirin continues and can affect the body.

Liver Processing

• Aspirin-rich blood enters the liver via the hepatic portal vein and exits through the hepatic vein.

• The liver acts like a filter that metabolise drugs through a process called first-pass metabolism.

Phase One Metabolism

• Aspirin is hydrolyzed, removing ethanoic acid and producing salicylic acid (not yet water-soluble for excretion).

Phase Two Metabolism

• An ionized group is added to the salicylic acid, forming glucuronide, making it water-soluble and suitable for urinary excretion.

• Due to the filtering, only 68% of orally administered aspirin effectively reaches the body. This measurement is known as the drug's oral bioavailability.

Alternate Drug Administration

• Drugs given through routes other than oral (e.g., intravenously or buccally) can bypass the small intestine and liver entirely, achieving 100% bioavailability.

Effect on Skin Tissue and Pain

• At the site of skin tissue damage, prostaglandins are produced, causing inflammation and transmitting pain signals to adjacent nerves.

• Upon reaching the site, aspirin inhibits the production of prostaglandins, reducing swelling and alleviating pain signals.

Excretion

• Remaining aspirin circulates through the bloodstream and returns through the liver multiple times until utilized or filtered out from the body.

• The process continues with aspirin traveling to the kidneys and subsequently into the bladder for excretion.