1 Tobacco smoke contains tar, carbon monoxide and nicotine. 2 Tar settles on the epithelium lining the bronchi and bronchioles and stimulates inflammation, an increase in the secretion of mucus and an accumulation of phagocytes from the blood. 3 Damage to the airways and alveoli occurs in...

Smoking  is one of the major avoidable  risk factors of chronic,  life-threatening diseases of the gas exchange and circulatory systems.The smoke from cigarettes contains several substances that affect the gas exchange system and the cardiovascular system. These include:• tar, a mixture of substances including...

1 Multicellular organisms often have surfaces that are specialised to allow exchange of gases to take place between their bodies and the environment. Alveoli in the lungs form the gas exchange surface in mammals. 2 In the human lungs, air passes down the trachea and through a branching system of...