Every time a person has a cigarette, changes happen in their body.
Carbon monoxide levels in the lungs increase. Carbon monoxide is a colourless, odourless, poisonous gas that is quickly absorbed into the blood replacing oxygen. This means that the heart has to work harder to get enough oxygen to the muscles, brain heart and other organs. The breathing in of carbon monoxide from tobacco smoke in the air by a non-smoker has a similar effect.
Nicotine is quickly transported around the body and reaches the brain within ten seconds of the first puff. Nicotine causes an increase in heart rate and blood pressure. It also slows circulation in the smaller blood vessels. Nicotine can act both as a relaxant, relaxing skeletal muscles, and as a stimulant, increasing tension in other muscles. Stomach secretions are increased and there are changes to brain activity.
Tobacco smoke also increases resistance in the airways leading to the lungs and reduces lung capacity.