Toxicology Flashcards
What is poison?
any substance which, if taken into/formed in the body, destroys life or impairs health
What are the 5 types of poison?
1) Corrosives: Powerful chemicals that destroy tissues
2) Irritants: Ingested - irritant to gut, causing nausea & diarrhoea
3) Systemic poisons: Attacks a certain biochemical systems (e.g. CO binds to haemoglobin)
4) Toxins: Poisons produced by living organisms
5) Venoms: Poisons delivered by bites & stings
How is carbon monoxide produced?
Comes from partial combustion of fuel/other organic material
How is CO poisonous? (2)
1) 4 Haem units in each haemoglobin protein = each unit is an iron atom held together by 4 nitrogen atoms. Haem unit picks up oxygen molecule; oxygen binds to iron
2) The iron atom binds to CO more strongly than O2. CO blocks the site on the iron and prevents O2 from being taken up, forming carboxyhaemoglobin irreversibly
How is carbon dioxide poisonous?
if present in high concentration, can lead to asphyxiation
How does our body react to venom if ingested?
Since venom is a protein, it will be rapidly broken down into amino acids by enzymes in the digestive system
What is the difference between poison and remedy?
anything can be poison, depending on dose
How do we measure toxicity?
LD50: Amount needed to kill half a given population of test animals. Quoted in terms of weight of poison per unit body weight
What are 5 factors that affect the dose needed to poison someone?
1) Size: larger doses for larger bodies
2) Age: metabolism changes with age
3) State of health: especially condition of the liver
4) History: build up/loss of tolerance. If one’s body is accustomed to a toxin, it will take a higher dose to kill him
5) Paradoxical reactions: opposite of what is expected (rare but known)
What are the 3 conditions needed for poison to work?
1) absorption into the body
2) reach the target organ
3) build up in the target organ before excretion (rate of build up must be > rate of excretion)
What are 4 routes of poison administration?
1) Oral administration: absorbed through digestive tract
2) Intravenous (injection): directly into blood stream. Efficient
3) Inhalation: rapidly from lungs to blood
4) Through mucus membranes: often fast & efficient
How does the stomach & small intestine work with/against poison?
The stomach and small intestine processes proteins to peptides & amino acid saccharides for absorption. Sometimes, the body can break down poison into harmless substances. Hence, if not absorbed, the poison will not be effective.
How does the liver work against poison?
Anything absorbed from the intestine will be flowed to the liver for detox (chemical transformations). The liver can make toxic products non toxic, where it can be easily excreted
Why is poison delivered by breathing more potent than ingestion?
Blood flow: intestine -> liver -> lungs
Lungs come after the liver in blood flow. Hence, whatever enters the lungs goes straight into bloodstream before it enters the liver
What are xenobiotics?
Molecules that the body recognises as “strange”, not naturally produced by the body & not supposed to be there
What are the 3 ways the body deals with xenobiotics?
1) Accumulate: e.g. lead or Strontium in bones
2) Excrete: Arsenic or Thallium in hair (not in the body)
3) Transform: increase solubility to be excreted (liver’s job)
What is the biological effect of alcohol?
depresses the central nervous system
How is alcohol distributed in the body?
At first, it is absorbed by stomach (20%) and small intestine (80%). It appears in the blood in minutes; complete in 30-60min. Blood will distribute alcohol uniformly throughout the body, except bones, fat and hair
What are 3 ways to measure alcohol concentration level in one’s body?
1) Measure blood alcohol = concentration in the brain (Gas chromatography)
2) Measure breath alcohol (measured by police on roadside)
3) Post mortem: blood, urine, vitreous humour
How is alcohol eliminated from the body? (2)
1) 2-5% is lost through kidneys (urine) & lungs (breath)
2) Most of ethanol will be converted into acetaldehyde by alcohol dehydrogenase (an enzyme in liver & small intestine. It will further oxidise into acetic acid by aldehyde dehydrogenase (liver). Acetic acid can be handled by the body (part of our normal metabolism). Further broken down into CO2, which is exhaled
What is the alcohol limit in Singapore? (2)
35 mg of alcohol per 100 ml of breath, or 80 mg of alcohol per 100 ml of blood.
How do we calculate blood alcohol level?
c = a/pr
c = maximum concentration (g/1000ml)
a = amount of alcohol taken (g)
p = person’s weight (kg)
r = widmark factor
What is the Widmark factor (r)? What is the factor for men and women?
Proportion of total body mass over the body mass which the alcohol can be distributed.
men: 0.68
women: 0.55 (due to higher proportion of fatty tissue, which cannot absorb alcohol)
What is Henry’s law?
For solutions at low concentrations, the vapour pressure of the solute is proportional to its mole fraction. More alcohol dissolved in blood = proportionately more alcohol in breath
