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Absorption, Distributiom and Excretion of Toxicants

6 important questions on Absorption, Distributiom and Excretion of Toxicants

What is the role of blood flow and ionisation in xenobiotic absorption?

during the transfer from the site of exposure to the systemic circulation, toxicants may be eliminated. The gastrointestinal mucosa and the liver may eliminate a significant fraction of a toxicant during its passage through these tissues, decreasing systemic availability. particles smaller than 2 µm can penetrate into the alveoli from where they can be taken up via alveolar epithelium.
De degree of which toxic susstances taken in orally are absorbed in the digestive tract is mainly determined by their liphilicity

What is influencing distribution of toxicants?

it depends on blood flow, diffusion out of capillary bed into the cells,active transport into cells, volume of distribution, binding to plasma and tissue proteins, storage in tissue and specific barriers.

blood-brain barrier = this is less permeable due to the tight junctions, no fenestrae, low protein content interstitial fluid mainly active transport. this barrier is not fully developed at birth

placental barrier = it's not really a good barrier cause passive diffusion happens very easily (alcohol easily crosses the barrier)

Where are toxicants in the body storage?

- Liver and kidney = these organs have a high capacity for binding and accumulation of toxic substances. they have this more than any other organs. This is probably due to the fact that they have an important role in the elimination of toxic substances.

- fatty tissue = substances with a high octanol/water partition coefficient often accumulate in fatty tissues. the substances accumulate by simple dissolving in neutral lipids.

- bone tissue = bone tissue is an important accumulation site especially for metals such as lead and strontium, but also for fluorine

Call the process for excretion by various organs?

main routes of excretion are the kidney, the GI tract and the lungs

kidney = urinary excretion

liver = bile = fecal excretion

lung = exhalation

other routes = cerebrospinal fluid, mother's milk, sweat and saliva

What is blood-brain barrier?

is not an absolute barrier to the passage of toxic agents into the CNS. Instead it represents a site that is less permeable than are most other areas of the body

What is placental barrier?

most toxic agents pass the placenta by simple diffusion. it is uncertain whether the placenta plays an active role in preventing the transfer of noxious substrates from mother to foetus. However, the placentas has bio transformation capabilities that may prevent some toxic substances from reaching the foetus

The question on the page originate from the summary of the following study material:

general toxicology | WUr

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