It is important to remember that the stomach gastric juice is very acidic and the intestine is more neutral to slightly basic.
Chemicals that are called WEAK ACIDS (when given orally) will only be absorbed in the acidic stomach.
Chemicals that are called WEAK BASES (when given orally) will only be absorbed in the alkaline intestine.
There are many other factors to consider regarding chemicals found in food besides whether they are weak acids or weak bases.
Firstly, the chemical may be intermixed with food that we consume.
For example, a protein rich meal tend to stay in the stomach for hours before moving into the intestine. This fact will slow down the expected absorption of a weak base - because it cannot be absorbed until it moves with the food from the stomach into the small intestine.
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
I would like to point out that drug development takes into consideration all aspects of absorption, metabolism, action etc. However, if I change focus from drugs to a chemical which may be a poison or carcinogen or just outright dangerous to man.The liver has many options that it may use to handle a chemical - drug or potentially harmful chemical.
If the toxicant is water soluble it can be sent to kidney to be excreted in urine.
If the toxicant is lipid soluble, the liver will attempt to make it water soluble to send it to the kidney.
If it can't a couple of options exist. The lipid soluble toxicant can be put into bile and released with the next fatty meal back into the small intestine. If however the lipid soluble toxicant is reabsorbed and sent back to the liver - we are back where we started.
Another option is for the liver to combine the toxicant with triglycerides and use the lipoprotein VLDL (Very Low Density Lipoprotein) to carry it to store in our adipose (fat) tissue.
Remember however that the adipose tissue may be in the brain, breasts, or hips, buttocks, etc.
Whereever it is sent, it is stored there as an unchanged toxicant, that can be re-released any time a person loses weight.
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.