Deck 3: Toxicology Terms and How They Relate to Organisms

Question 1

What is a probit and why is it important in toxicology measurements?

Answer 1

A probit is a standard deviation unit. Populations of living creatures with diverse genetic backgrounds respond based on probits rather than increase toxicity linearly by percent of the population. This means that most animals of a species die at the LD₅₀ and trail off on either side of this value based on standard deviation units from this value.

Question 2

What is an IC₅₀? Is it the same as an EC₅₀ or an LC₅₀?

Answer 2

The concentration that causes 50% inhibition of an enzyme or function may be higher or lower that the toxic concentration that may cause illness (EC₅₀) or lethal concentration (LC₅₀) that causes half of cells or half of animals in an ecosystem to die depending on the enzyme and its link to vital functions of that cell or animal. In bacteriology the I₅₀ can refer to a concentration that effects the growth curve of bacteria by half of untreated bacteria.

Question 3

What is an agonist and antagonist and how can both be toxic?

Answer 3

An agonist has the true physiological function of a substance at a receptor such as amphetamine has similar effects of dopamine. Both affect neurological and cardiovascular functions and can cause organ damage or death based on dose or doses over time. An antagonist blocks the action of a substance at a receptor such as a beta-blocker blocks the action of norepinephrine or epinephrine on the heart and thereby slows the heartbeat. At high doses, the heart can slow to create hypotension and cardiac arrest/death.

Question 4

Which common medication that can be bought over-the-counter at a drug store are therapeutic as a dose and toxic as a dosage and which are therapeutic as a dosage but toxic as a dose?

Question 5

Why is the log P or log K_OW an important factor in determining the bioavailability or toxicity of a compound?

Question 6

Why is the MTD a controversial way of dosing an animal to assess toxicity?

Question 7

Why might the toxicity of a substance actually drop with repeated exposures?

Question 8

Why is TD₅₀ determined for human while the LC₅₀ is considered with environmental organisms?