Hepatic portal vein : an explanation

This is an attempt to explain how things absorbed from the gut end up in the hepatic portal vein awaiting assessment by the liver, before then entering the main circulation.

The body will do all it can to keep the main circulating blood as clean as possible. With regards to the things absorbed from the gut, it has 2 main ways of making sure the absorbed material is as clean as possible before entering the main circulation: The gut wall barrier, and the hepatic portal vein 'waiting room', which is where all the absorbed material ends up and is then procesed by the liver, usually by the xenobiotic enzymes altering them

1. The gut wall barrier: Simply stops molecules too big from being absorbed into the portal vein when working correctly.
2. The portal vein: You can think of it as a waiting line for a screening check by the liver, before entrance to the main circulation. These molecules will (usually) be absorbable size, and for the most part the xenobiotic enzymes of the liver will then alter (neutralizing) the 'baddies' and possibly activate the 'goodies' (if need be). Once assessed and altered by the liver, it then enters the main bloodstream.

It's probably not as simple as that, but in general that's probably what mostly happens.

contents of the gut >>
gut wall keeps molecules too big from being absorbed (this is where leaky gut is a concern) >>
then enters the hepatic portal vein awaiting assessment by the liver>>
then the liver alters/neutralizes/activates the molecules >>
only then enters the main circulation

http://encarta.msn.com/dictionary_1861737853/portal_vein.html
http://en.wikipedia.org/wiki/Hepatic_portal_vein