作业帮肝肠循环和首过效应关系
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肝肠循环和首过效应关系
肝肠循环和首过效应关系
肝肠循环和首过效应关系
Enterohepatic circulation
Substances that undergo enterohepatic circulation are metabolized in the liver (usually by conjugation),excreted in the bile,and passed into the intestinal lumen (where the intestinal bacteria break some of the conjugated drug,releasing the unmetabolized drug again) where they are reabsorbed across the intestinal mucosa (thus returns to systemic circulation again) and returned to the liver via the portal circulation.Drugs may remain in the enterohepatic circulation for a prolonged period of time as a result of this recycling process.thus increase in their halflives.
First pass effect:
After a drug is swallowed,it is absorbed by the digestive system and enters the portal circulation.The absorbed drug is carried through the portal vein into the liver.The liver is responsible for metabolizing many drugs.Some drugs are so extensively metabolized by the liver that only a small amount of unchanged drug may enter the systemic circulation,so the bioavailability of the drug is reduced.Alternative routes of administration (e.g.,intravenous,intramuscular,sublingual) avoid the first-pass effect.
mainly when say metabolised that means deactivated drug,thus in case of enterohepatic circulation drug is deactivated in liver then reactivated in intestine so increase the effect,and in case of first pass effect its deactivated in liver thus decrease effect.