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CHEMICALS ABSORBED THROUGH THE GASTROINTESTINAL TRACT

Many chemicals can be absorbed through the gastrointestinal tract.
It is important to remember that the stomach gastric juice is very acidic - and this condition will favor absorption of chemicals that are WEAK  ACIDS
The intestine is more neutral to slightly basic - and this condition favors the absorption of chemicals that are WEAK BASES.
There are many other factors to consider regarding chemicals found in food.
Firstly, the chemical may be intermixed with protein.  If this is the case, protein rich meals tend to stay in the stomach juice for hours before moving into the intestine.  One must also consider the possibility that the acid conditions of the stomach may alter the the toxicant. The altered toxicant may not be absorbed but may interfere with absorption of a needed nutrient or may be more dangerous than the original form of the toxicant.
One should also note that once any chemical  has been absorbed from the gastrointestinal tract, it enters the blood stream and is immediately brought to the LIVER.

The liver is the largest of our internal organs and has several important functions, including:
  - biotransformation and detoxification of chemicals
- formation of bile
- protein synthesis
- filtration
- maintenance of nutrient balance

The liver has many options that it may use to handle a toxic chemical.
It may change it, from a lipid soluble form to one that is water soluble - hence allowing the kidney to excrete it from the body.
If the liver can't change it from a lipid soluble form into a water soluble form, it may combine it with triglycerides and use the  lipoprotein VLDL ( Very Low Density Lipoprotein) to carry it to storage in our adipose (fat) stores.

It may also try to excrete the lipid soluble chemical through  the gall bladder by combining it with bile.
This mechanism would cause the chemical - now in bile - to be released back into the intestine with the consumption of our next lipid meal, hopefully then to be eliminated in feces.

If the liver has not been successful in causing the toxicant to be eliminated from the body, either via the kidney or back into the intestines, and the toxicant has been stored in our fat tissues - it may remain in our bodies for a long time - as a potential time bomb. For example, if a person has been  chronically exposed to a lipid soluble toxicant that can cause depression and the liver was unable to cause changes in its chemical characteristics and it has stored it in adipose tissues. As long as it is stored, no depressive effects will be seen. BUT, if the person goes on a weight reduction program, and adipose tissue is destroyed, the depressive toxicant will once again produce its effects.
These "flashback effects"  have been seen with many lipid soluble drugs that are either stimulants or depressants, and similar effects with toxicants cannot be ruled out.

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