23 June 2013

#83 Effects of tobacco smoke on the respiratory system

Tobacco smoke contains irritants and carcinogens

Its 4 main toxic chemicals: carbon monoxide, nicotine, smoke particles and tar.

Carbon monoxide:
- combines with haemoglobin in RBC ---> prevents them transporting O­2­.

- addictive ---> continual smoking

Smoke particles:
- irritate air passages ---> inflammation + increase mucus production ---> chronic bronchitis.
- presence of smoke particles in alveoli + coughing = emphysema (breathlessness)

- a carcinogen: increase risk of lung cancer ( cell division out of control)
- lines air passages:
    - increase mucus production
    - paralysing + damaging cilia
    ---> bronchitis

Some of the substances in tobacco smoke.  

Common misconceptions
Remember that only nicotine and carbon monoxide enter the blood. Tar and smoke particles do not – they stay in the lungs. 

Sample question

The table shows the percentage of haemoglobin which is inactivated by CO present in the blood of taxi drivers in a city. 

City taxi drivers
Percentage of Hb inactivated by CO
Daytime drivers
Night-time drivers

i) Suggest two sources of the CO inhaled by these taxidrivers          [2marks]
ii) Some daytime drivers have 5.8% of their Hb affected. Using information from the table, explain which source contributes most to this effect.        [2 makrs]
iii) Suggest a reason for the differences, shown in the table, between daytime and night-time drivers.                                                                          [1 mark]

Studen’s answer

i) 1. cigarette smoke ü
   2. breathing by passengers û
ii) It must be cigarette smoking because non-smokers have less of their Hb affected. ü
iii)Therer could be less car exhaust fumes, containing CO, at night. ü

Examiner’s comments

In part (i), the second answer if biologically incorrect (we breath out CO2, not CO. The other correct answer was car exhaust gases.
In part (ii), the answer and the explanation were correct.
Part (iii) war a good answer.

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