Edexcel IGCSE Biology 复习笔记 2.7.6 Smoking & the Human Gas Exchange System

Edexcel IGCSE Biology 复习笔记 2.7.6 Smoking & the Human Gas Exchange System

Smoking & the Gas Exchange System


  • Smoking causes chronic obstructive lung disease (COPD), coronary heart disease and increased risks of several different types of cancer, including lung cancer
  • Chemicals in cigarettes include:
    • Tar - a carcinogen (a substance that causes cancer)
    • Nicotine - an addictive substance which also narrows blood vessels
    • Carbon monoxide - reduces the oxygen-carrying capacity of the blood






  • Nicotine narrows blood vessels leading to an increased blood pressure
  • It also increases heart rate
  • Both of these effects can cause blood clots to form in the arteries leading to heart attack or stroke




Carbon monoxide

  • Carbon monoxide binds irreversibly to haemoglobin, reducing the capacity of blood to carry oxygen
  • This puts more strain on the breathing system as breathing frequency and depth need to increase in order to get the same amount of oxygen into the blood
  • It also puts more strain on the circulatory system to pump the blood faster around the body and increases the risk of coronary heart disease and strokes





  • Tar is a carcinogen and is linked to increased chances of cancerous cells developing in the lungs
  • It also contributes to COPD, which occurs when chronic bronchitis and emphysema (two different diseases which are frequently linked to smoking) occur together
  • Chronic bronchitis is caused by tar which stimulates goblet cells and mucus glands to enlarge, producing more mucus
    • It destroys cilia and mucus (containing dirt, bacteria and viruses) builds up blocking the smallest bronchioles and leading to infections
    • smoker's cough is the attempt to move the mucus


  • Emphysema develops as a result of frequent infection, phagocytes that enter the lungs release elastase, an enzyme that breaks down the elastic fibres in the alveoli
    • This means the alveoli become less elastic and cannot stretch so many burst
    • The breakdown of alveoli reduces the surface area for gas exchange
    • As it progresses, patients become breathless and wheezy - they may need a constant supply of oxygen to stay alive







The breakdown of alveoli in emphysema reduces the surface area for gas exchange