What harm does tar cause?
Short-term effects:
Tar is a combination of chemicals, which settles on 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 muscles in the walls of the airways to contract. The lumen of the airway 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 and the mucus-secreting glands to enlarge and release more mucus. This mucus collects in all the airways.
Bacteria and viruses that become trapped in the mucus are not removed. They can multiply in the mucus, and eventually a combination of mucus and bacteria may block the bronchioles. The presence of bacteria and viruses means that the lungs are more susceptible to infection. Smokers are more likely to catch diseases such as influenza or pneumonia.
Long-term effects:
Smoker’s cough is an attempt to shift the bacteria laden mucus that collects in the lungs. It results from the irritation to the airways by the mucus and bacteria, as well as from the need to clear the airways in order to get air down to the alveoli.
Unfortunately, a constant 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 layer 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 epithelium. Also, it attracts white blood cells. These are brought in to deal with pathogenic microorganisms.

What diseases are associated with smoking?
Disease
Cause
Symptoms
Long term risk
Chronic Bronchitis
The Inflammation of the lining of the airways. This is accompanied by the damage to the cilia and the overproduction of mucus, so that mucus collects in the lungs.
Irritation in the lungs.
Continual coughing.
Coughing up mucus that containing bacteria and white blood cells.
It can lead to an increased risk of lung infection.
Emphysema
The loss of elasticity in the alveoli. This causes the alveoli to burst. The lungs have a reduced surface area as larger air spaces are formed. This means there is less surface area for gaseous exchange.
Short of breath, especially when exerting themselves.
The loss of elasticity in the alveoli makes it harder to exhale.
In severe cases, the breathing will become more shallow and rapid.
Lung cancer
Cigarette smoke contains a lot of carcinogenic compounds that cause cancer. They enter the nucleus of these cells and have a direct affect upon the genetic material. Any change to the genetic material is called a mutation. If the mutation affects the genes that control cell division. Then uncontrolled cell division may take place.
Lung cancer can be recognised by continual coughing and a shortness of breath. There may be pain in the chest and blood coughed up in the sputum. This blood is often the first sign that alerts a person to the possibility of lung cancer.
Lung cancer often takes 20-30 years to develop and a cancer may have been growing years before it is discovered.
COPD
COPD is a combination of diseases that include chronic bronchitis, emphysema and asthma.
The symptoms are a combination of the symptoms of the disease specified in the left column.

Atherosclerosis
Smoking can damage the walls of your arteries. Blood cells known as platelets will then clump together at the site of the damage to try to repair it. This can cause