Biology- The effects of smoking

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Cigarette smoke:

Cigarette smoke contains over 4000 different chemicals. Many of these are harmful. The harmful substances in cigarette smoke include:

·         Tar, which is a mixture of chemicals including carcinogens.

·         Carbon monoxide.

·         Nicotine.


What harm does tar cause?

Short-term effects:

Tar is a combination of chemicals, which settles in the lining of the airways and alveoli. This increases the diffusion distance for oxygen entering the blood and for carbon dioxide leaving the blood.

The presence of many chemicals in the tar lying on the surface of the airway may cause an allergic reaction. This causes the smooth muscle in the walls of the airways to contract. The lumen of the airways gets smaller and this restricts the flow of air to the alveoli.

The tar paralyses or destroys the cilia on the surface of the airway, so they are unable to move the layer of mucus away and up to the back of the mouth. The tar also stimulates the goblet cells to secrete more mucus, and this mucus collects in the airways.

Bacteria and viruses that become trapped in the mucus are not removed. They can multiply and eventually a combination of mucus and bacteria may block the bronchioles.

The presence of bacteria and viruses mean that the lungs are more susceptible to infection. Smokers are more likely to catch diseases such as influenza or pneumonia.


Longer-term effects:

Smokers cough is an attempt to shift the bacteria-laden mucus that collects in the lungs. It results from the irritation of the airways by the mucus and bacteria, as well as from the need to clear the airways in order to get air down into the alveoli.

Unfortunately, a persistent cough produces its own effects/. The delicate lining of the airways and alveoli can become damaged. The lining will eventually be replaced by scar tissue, which is thicker and less flexible. Also, the layer of smooth muscle in the wall of the bronchioles thickens. This reduces the lumen of the airway, and the flow of air is permanently restricted.

Frequent infections brought about by the presence of bacteria and viruses in the mucus will inflame the lining of the airways. This damages the lining, and in particular, the layer of the epithelium. Also, it attracts white blood cells. These are brought in to deal with pathogenic microorganisms. The white blood cells have to


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