Lecture 4B: Toxicokinetic Flashcards
Physiochemical Factors
- Lipid Solubility/hydrophobicity
- Degree of ionization
- Size/Shape
- Charge/polarity
- Structure similarly to endogenous molecules
Four Phases
– Absorption
– Distribution
– Metabolism (Biotransformation)
– Excretion
Toxicokinetics (TK)
The study of how the body treats toxins/toxicants that enter and the factors that may influence the concentration of a toxin at its site of action.
Xenobiotic
This is any foreign substance that is present in the body.
Target Site/Organ
the site/organ on which the toxin/toxicant elicit its toxic effect.
After absorption lead enters the blood and ___ is taken up by red blood cells (RBCs).
97%
What is the half (½) life of lead?
2-3 weeks
What happens during the half life?
there is redistribution to liver and kidney, then excretion into bile or deposition into bone.
After an initial, reversible uptake into bone, lead in the bone will
become incorporated into the hydroxyapatite crystalline structure
Past exposure to lead can be detected via _____ and ___.
X-ray analysis and blood and urine analysis.
How does lead become detectable in blood & urine analysis?
The amount in blood representing current exposure.
Organs and systems destroyed by lead
kidney, testes, bones, gastrointestinal tract and
the nervous system.
Lead causes significant biochemical effects like
Being the interference with haem-synthesis giving rise to anemia
Acute exposure to inorganic lead results to
renal damage particularly to the proximal tubules
Lead adversely affects
reproductive function in both males and females
Treatment/Detection of Lead
- X ray to detect or blood/urine test then -
- Bowel irrigation polyethylene glycol solution
- Gastric lavage
- Chelation therapy- bind to lead then excreted in urine
- Activated charcoal – bind to lead in GI then administer cathartics
- EDTA- Ethylenediaminetetracetic acid
What is a cell membrane?
The structure called the phospholipid bilayer, which is amphiphilic.
Xenobiotics pass through cells located
at the sites of various routes to ultimately reach the target site.
The cell membrane contains ______ heads and ______ tails.
hydrophilic and hydrophobic
The heads of the cell membrane are turned
outwards, facing the extracellular environment.
The tails of the cell membrane are turned
inwards to the intracellular environment.
The membrane also contains important proteins called
transverse proteins
Transverse proteins aid in
the transport of substances
Two modes of Transport in cell membrane
Passive and Special Transport
Types of Passive Transport
Filtration & Simple Diffusion
Types of Special Transport
Active transport & Facilitated Diffusion
What is an ion pump?
An enzyme that uses ATP to move ions across the cell membrane
What is ion gates?
flow of ion across cell membrane
Passive Transport
The movement of substances (toxins/toxicant) across a cell membrane without the use of energy by the cell
Filtration
The passage of molecules from one environment to another through a porous membrane due to osmotic pressure or hydrostatic forces.
Simple Diffusion
movement of a solute from an area of high concentration to an area of low concentration
The lipid solubility of larger compounds will determine
the rate of transport across the membrane.
What factors that must be met for simple diffusion:
- There most be a concentration gradient
- Must be lipid soluble
- Must be non-ionized
Only _______ will go down the concentration gradient.
non-ionized lipid soluble compounds
Partition Coefficient refers to
the solubility of a compound between two immiscible environments.
Positive co efficient values are associated with
high lipid solubility
Negative values co efficient are associated with
low lipid solubility
More positive Partition Co-efficient are
more lipophilic
Degree of Ionization
Many compounds/chemicals are weak acids or bases. This also applies to toxins/toxicants.
The ionized form of a toxin usually has
low lipid solubility
Why is degree of ionization important?
This determines the extent of absorption, as only the non-ionized form will be able to pass through the lipid bilayer by passive diffusion.
Toxins/Toxicants low in lipid solubility may cross the cell membrane, but at
slow inefficient rates. This would aid in preventing a toxic effect.
