Question

Why does blood flow affect absorption of drugs taken orally?

Answer 1

Blood flow is important for actively absorption of medicines. Gastrointestinal tract have higher perfusion rate because it is massively supplied by blood capillary network which help in preserving sink conditions and concentration gradient for drug absorption by swifly removing of drug from site of action.

The drug is absorbed from the small intestine first then it enters the mesentric vein (main function is to drain blood from the intestine) to the hepatic-portal vein (responsible for directing blood from the spleen) and then to the liver before reaching the circulation system or the heart. If there is a decrease in mesenteric blood flow the rate of drug removal from the intestine will also decrese which wil reduce the drug bioavailability.