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

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

Ciliated Cells

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 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

Smoking & the Gas Exchange System (Edexcel IGCSE Biology)