How Tobacco Causes Diseases

It is worth having a simple model of tobacco-caused diseases in mind, as there are so many of them that it may cause confusion. Tobacco diseases are best seen as the inhalation of toxic substances, some of which act immediately, and some of which have effects in the longer term. 

1. The Toxic Ingredients are. 

a. Hot gases, which directly irritate and harm mucosa

b. Tar, which contains substances that cause cancer

c. Carbon Monoxide, a poisonous gas, which inactivates red cell oxygen carrying capacity, and is directly toxic to cells especially those lining both the airways and the blood vessels

d. Nicotine, which resets the nervous system excitability, and the tone (tension) in the blood vessel walls. It is carried in the tar fraction and is responsible for addiction.

e. Particulate matter, which is deposited as soot. 

These five ingredients are inhaled actively or passively, and cause a number of diseases, which can be listed in order of the tissues that they come in contact with. 

2. Input cancers are caused as the smoke goes in to the body

Cancer of the lips, mouth, pharynx, larynx, bronchi and lung as the tar and hot gases meet the tissues directly. 

Cancer of the oesophagus (gullet) and stomach as the tar-laden saliva is swallowed. 

3. Lung damage 

Airway damage is caused by poisoning of airway lining cells with carbon monoxide, tar and nicotine and deposition of soot particles.  The smooth muscle in the airways is also contracted by nicotine. This leads to an inability to remove secretions with blockages causing recurrent infections leading to chronic bronchitis and trapping of air, which is called emphysema. The lung changes are also called Chronic Obstructive Pulmonary Disease (COPD) or sometimes Chronic Obstructive Airways Disease (COAD). It is different from lung cancer mentioned above.

4. Arterial diseases 

The tar, nicotine and carbon monoxide cross from the lungs into the bloodstream. The tar and carbon monoxide may directly damage the blood vessel walls, and change the platelets (clotting cells) so that they stick to the blood vessel walls. The smooth muscles in the blood vessel walls are contracted by the nicotine, so the lumen (hole the blood goes through) is smaller. Hence the pressure is higher (due to the same volume having to pass through a smaller pipe), and the flow more turbulent. The arterial effects of smoking are thus caused by reduced blood flow, by complete blockage of arteries or by the weakening of the blood vessel walls so that they dilate or rupture as an aneurysm. This process affects a large number of organs. The organ affected depends on which artery is affected. 

Stroke - due to damage to cerebral arteries to the brain

Skin ageing - due to reduced skin blood flow 

Heart disease - This is worsened by nicotine as the heart has an increased load as the blood vessels contract, but the heart also receives less blood itself through the contracted coronary arteries. 

Kidneys - these regulate blood pressure, so damage to these (renal) arteries has a compounding effect, as the kidney produces hormones that increase the body's blood pressure to maintain kidney blood flow. 

Uterus - reduced blood flow leads to smaller babies, more prone to all neonatal problems. 

Impotence - reduced blood flow to the penis is a major cause of impotence 

Gangrene - usually of the legs, but also of the fingers in some cases 

Fractures - slower healing and an increased incidence of non-union due to reduced blood flow, even in young patients 

Slower wound healing after surgery due to reduced blood flow and poisoning of healing cells by carbon monoxide.  The is also a greater chance of abdominal wound rupture because smokers cough more after anaesthetics.

Increased chance of blood clots.  These often start in the legs (deep venous thrombosis) and break off and block arteries in the lungs (pulmonary embolism).  This can happen particularly after surgery or immobility such as flying.  It is caused by carbon monoxide poisoning the cells lining the arterial walls, so the platelets stick to them and form the clots.

5. Direct toxic effects while tar is circulating 

Leukaemia- as the tar fraction affects dividing blood cells 

Babies - foetal abnormalities are increased 

Increased fractures - particularly of the hip and vertebrae in older smokers due to acid/base effects where calcium is mobilised. This is because damaged lungs retain carbon dioxide which reacts with water to form carbonic acid which lowers the pH and makes the bones' calcium more soluble.

6. Output Cancers - are caused by tars as they leave the body in secretions. The unpleasant smell on the skin of smokers is due to the tars coming out of the sweat glands. All body secretions are filtrates of the fluid outside cells, which is concentrated, thus making the cells lining the secretory glands exposed to higher tar concentrations. This results in an increased chance of: 

Cancer of the urinary bladder

Cancer of the pancreas

Cancer of the breast

Cancer of the cervix

Cancer of the prostate 

7. The Addictive Component is nicotine. Thus the trying of it and the temporary adolescent belief of its image-giving properties gives time for a re-setting of nerve outputs. By definition, an addictive substance gives a withdrawal syndrome, as the nicotine level falls. This is why nicotine supposedly 'relieves stress'. It removes the 'stress' of the withdrawal syndrome. This is important in keeping people smoking.

So this is why there are no many diseases caused by smoking tobacco. 

If you have not started, don't and if you have, it is never too late to quit.