Smoking & the Gas Exchange System (Edexcel IGCSE Science (Double Award): Biology): Revision Note

Smoking & the Gas Exchange System

• Smoking cigarettes has been linked to disease in the lungs, and is also a risk factor in coronary heart disease

• There are many harmful chemicals in cigarettes that are linked to disease, e.g. 

  •  nicotine:

    • narrows blood vessels and increases heart rate, leading to increased blood pressure

    • causes high blood pressure that leads to blood clots forming in the arteries, potentially resulting in heart attack or stroke

  • carbon monoxide:

    • binds irreversibly to haemoglobin, reducing the capacity of blood to carry oxygen

    • puts more strain on the breathing system, as breathing frequency and depth need to increase to supply the same amount of oxygen

    • means that the circulatory system needs to pump blood faster, raising blood pressure and increasing the risk of coronary heart disease and stroke

  • tar:

    • is a carcinogen linked to increased chances of cancerous cells developing in the lungs

    • contributes to COPD, which occurs when chronic bronchitis and emphysema occur together

Diseases of the gas exchange system linked to smoking

Chronic bronchitis 

• Tar stimulates goblet cells and mucus glands to enlarge and produce more mucus

• Mucus builds up, blocking the smallest bronchioles and leading to infections

  • The build-up of mucus can result in damage to the cilia, preventing them from beating and removing the mucus

• A smoker's cough is the attempt to move the mucus

In healthy airways cilia are present, and beat to move mucus up and out of the lungs; in smokers the cilia are damaged so mucus is not removed

Emphysema

• Emphysema is a result of frequent infection

  • Infections occur more frequently in smokers due to the build-up of mucus that occurs in the lungs

• Emphysema develops as follows:

  • phagocytes that enter the lungs release elastase, an enzyme that breaks down the elastic fibres in the alveoli

  • the alveoli become less elastic and cannot stretch, so many burst

  • the breakdown of alveoli reduces the surface area for gas exchange

• Emphysema patients become breathless and wheezy, and may need a constant supply of oxygen to stay alive

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