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Smoking is one of the major avoidable risk factors ofchronic, life-threatening diseases of the gas exchange and circulatory systems.

1. Describe the effects of tar and carcinogens in tobacco smoke on the gas exchange system with reference to lung cancer and chronic obstructive pulmonary disease (COPD)

  • Tar is a mixture of compounds that settles on the lining of the airways and in the lungs
  • Carcinogens are cancer-causing compounds that cause mutations in genes that control cell division

a) Chronic bronchitis

  • Tar stimulates the goblet cells and mucus glands to enlarge and secrete more mucous
  • Tar also inhibits the cleaning action of the ciliated epithelium
  • It destroys many cilia and weakens the sweeping action of those left
  • This causes mucus to accumulate in the bronchioles 
  • As mucus is not moved, or moved very slowly, dirt, bacteria and viruses collect and block the bronchioles
  • With time, the damaged epithelia is replaced by scar tissue and the smooth muscle surrounding the bronchi and bronchioles becomes thicker
  • The thickening of the aiways causes them to narrow and makes breathing difficult
  • Pneumonia easily develops in the accumulated mucus and when there is an infection in the lungs, the linings become inflamed and this further narrows the airways
  • Sufferers have a severe cough and produce large quantities of phlegm


b) Emphysema

  • The inflammation of the constantly infected lungs cause phagocytes to line the airways
  • To reach the lining of the lungs from the capillaries, phagocytes release the enzyme elastase which destroys elastin in the walls of the alveoli to make a pathway for the phagocytes to destroy the bacteria
  • Elastin is responsible for the recoil of the alveoli
  • When there is a small quantity of elastin remaining in the alveolar walls, the alveoli do not stretch and recoil during inspiration and expiration
  • As a result, the bronchioles collapse during expiration, trapping air in the alveoli which often burst
  • The surface area for gas exchange is greatly…


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