Simon Faxxy
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What are the differences between the composition of the blood which enters and leaves the liver?
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nexttime
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Do you mean the hepatic artery versus hepatic vein, or hepatic portal system?
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macpatgh-Sheldon
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Oc valid Q by @nexttime; however, as the hepatic artery/hepatic vein situation is similar to most other organs, I assume OP is asking about input via the portal system:-

One of the major functions of the liver (out of 10 odd) is detoxification. So blood entering the liver in the hepatic portal vein [coming from the alimentary tract], by something known as "first pass metabolism", is "cleaned up" before it reaches other vital organs like the heart and the brain, in order to avoid any toxins absorbed In the GI tract damaging the latter.

The enzymes that bring about this detoxification process are the in the microsomal fraction [derived by centrifugation from the ER], and are collectively called the cytochrome P450 system. These are one example of so-called phase 1 enzymes that oxidize, reduce or hydrolyse the offending internal or external toxin (mostly drugs). Individual ones that "attack" specific chemical types are now known e.g. the gene group CYP2D6 codes for an enzyme group that metabolizes several drugs e.g. beta-blockers and codeine [the latter is activated [by anabolism] to morphine, but most drugs are catabolized to inactivate them].

Phase 2 reactions in the liver [and to a lesser extent in other parts of the GI system and elsewhere] aim to make the chemical more water-soluble e.g. by glucuronidation, which makes it easier for the kidneys to get rid of it by filtration.

SO, IN SUMMARY, THE BLOOD LEAVING THE LIVER IS DEVOID OF TOXIC MATERIAL.

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nexttime
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(Original post by macpatgh-Sheldon)
Oc valid Q by @nexttime; however, as the hepatic artery/hepatic vein situation is similar to most other organs, I assume OP is asking about input via the portal system:-
Yes I knew - thought it might make the OP think about their question though!

SO, IN SUMMARY, THE BLOOD LEAVING THE LIVER IS DEVOID OF TOXIC MATERIAL.
Of course correct, and indeed, in those with porto-systemic shunts (i.e. those who don't have a portal system) it seems to be the build up of nitrogenous waste (and encephalopathy) that is the main problem, as well as general liver atrophy.

However I bet the answer also wants you to talk about the liver absorbing 'nutrients' or some such as well.
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