Blood perfusion, gastrointestinal tract

The tissue compartments included in the Johanson model are as follows the lungs, presumed to be the only site of uptake, and arterial blood the liver, presumed to be the only organ where transformation of 2-butoxyethanol takes place the gastrointestinal tract in equilibrium with the liver a group of richly perfused tissues a group of poorly perfused tissues a fat compartment and muscles and skin. Support... 

The tissue compartments included in the Shyr model are as follows respiratory tract liver gastrointestinal tract fat and a group of richly perfused tissues including kidney, bone marrow, and heart. Muscle and skin were separated into individual compartments to allow for the simulation of dermal exposure. The distribution of 2-butoxyethanol among compartments was assumed to be limited only by blood flow rate because the lipid solubility of 2-butoxyethanol allowed it to penetrate cell membranes rapidly. Liver was a major site of metabolism in the Shyr model with a minor amount of 2-butoxyethanol-glucuronide formed in the skin at the site of application for dermal exposure. 

Includes tissues that are not perfused with blood (such as bone [not including marrow]), body fluids (such as gastrointestinal tract contents, urine, bile, and blood in major vessels not included in any tissue group), and hair. 

PAHs reach more-perfused tissues rapidly following exposure and are eliminated more slowly from lessperfused tissues (Bartosek et al. 1984). A large fraction of orally absorbed benzo[a]pyrene is believed to be transported by lipoproteins from the gastrointestinal tract to the blood via the thoracic duct lymph flow (Busbee et al. 1990). 

The observation of fecal excretion of radioactive strontium of weeks to decades after an oral exposure or over shorter time periods after an intravenous exposure suggests the existence of a mechanism for transfer of absorbed strontium into gastrointestinal tract, either from the bile or directly from the plasma. Evidence for direct secretion of strontium from the plasma into the intestine is provided by studies conducted with the in situ lumen-perfused rat intestine. When the lumen of either the small or large intestine was perfused (below the entrance of the bile duct), in situ and radioactive strontium was injected intravenously, radioactive strontium was detected in the lumen, indicating that strontium was secreted from blood into the intestine (Palmer and Thompson 1961). The amount of strontium secreted into the small intestine was approximately 4-8 times that in the large intestine however, the strontium calcium secretion ratio was approximately 1 in the small intestine and 1.3 in the large intestine. The mechanism by which strontium is secreted into the intestine has not been determined. Transfer of strontium from the serosal (blood) side of the intestinal epithelium to the mucosal (lumen) side of the epithelium has been demonstrated in in vitro preparations of isolated rat colon mucosa. Serosal-to-mucosal transfer was observed to be completely... 

---