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
- nicotine:
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
