Approximately 10 million adults in Great Britain smoke, despite the fact that every year around 100,000 people in the UK die from smoking-related causes.

In order to get to grips with why smoking is bad for health, it is necessary to understand the respiratory system.

When someone takes a drag on a cigarette, tobacco smoke is inhaled through the mouth, pharynx and larynx into the trachea. This splits into two bronchi, one for each lung, and these tubes divide further until they are just 1mm wide. These are the bronchioles, which are composed of smooth muscle and are the point in the respiratory system that inhaled drugs can have an effect.

The bronchioles split further until they are only one cell thick. At this point €“ which marks the end of the breathing tubes €“ are alveoli, where gaseous exchange can take place thanks to the large network of tiny capillaries that carry deoxygenated blood from the heart via the pulmonary artery, and newly oxygenated blood to the heart via the pulmonary vein.

This is also the point at which the components of tobacco smoke, which include nicotine, carcinogens and other toxins, get into the blood and the body.