2 Flashcards
(17 cards)
what are the 3 phases that define fate of a toxic substance?
exposure
toxicokinetic
toxicodynamic
what is the exposure phase?
the moment at which the toxic substance comes into contact with the body
what is the toxicokinetic phase?
description of what rate a chemical will enter the body and what happens to it once it is in the body
absorption, binding, metabolism, excretion
what is the toxicodynamic phase?
forms the interactions of toxicants with the organism causing harmful effects
what it does to the structures in the human body
the nature of exposure is determined by the…
environment
physical state of the toxicant
nature of contact
routes of exposure:
GI tract
skin
lungs
what is the exposure dose?
dose present in the environment
what is the absorbed dose?
proportion of exposure dose that enters the living organism
absorption through the lungs:
rate? particles?
main site is alveoli (large surface area, thin membranes)
rate depends on solubility of gas
larger particles are deposited in URT / GIT
smaller particles are deposited in LRT
absorption through skin:
serves as continuous barrier to foreign compounds
dense network of keratin in outer layer of epidermis
polar substances diffuse through epidermis
non-polar substances diffuses through lipid matrix
dermis - porous, non selective, less of barrier
absorption through GIT:
facilitated by large surface area and thin membrane
ionisable substances will only be absorbed by passive diffusion if they are non-ionised at pH of particular site (weak acids + bases)
strong acids + bases are not usually readily absorbed from GIT by passive diffusion
factors affecting absorption in GIT:
aqueous solubility affects rate of absorption
large particle size may decrease absorption
food may facilitate or delay absorption
disease, infection or presence of other substances
absorption and passive diffusion:
rate?
main method for toxicants
rate is related to conc gradient and lipid solubility
absorption and filtration:
energy independent process
membranes of capillaries and glomeruli have large pores, allows small molecules to pass through
absorption and endocytosis:
particules engulfed by the cell
solid - phagocytosis
liquid - pinocytosis
energy dependent process
factors affecting distribution:
rate?
where toxicant is in circulation when it enters blood - skin, lungs, GIT - all enter different circulations
rate is dependent on = blood flow, chemical transfer, affinity
plasma proteins
why is the blood brain barrier difficult to breach?
capillaries feeding the brain are covered with processes of glial cell or astrocytes = reduces permeability
tight junctions = few pores
low protein conc = nothing to bind
