Effects of Tobacco Smoke

Smoking causes chronic obstructive lung disease, coronary heart disease and increased risks of several different types of cancer, including lung cancer
Chemicals in cigarettes include:
- Tar - a carcinogen (a substance that causes cancer))
- Nicotine - an addictive substance which also narrows blood vessels
- Carbon monoxide - reduces the oxygen-carrying capacity of the blood


Section through a normal lung	Section through a smoker’s lung

Tar is a carcinogen and is linked to increased chances of cancerous cells developing in the lungs
Tar also contributes to COPD, which occurs when chronic bronchitis and emphysema, two different diseases which are frequently linked to smoking, occur together
Chronic bronchitis is caused by tar which stimulates goblet cells and mucus glands to enlarge, producing more mucus
Tar destroys cilia, inhibiting the cleaning of the airways, and mucus (containing dirt, bacteria and viruses) builds up blocking the smallest bronchioles
A smoker's cough is an attempt to move the mucus but it damages the epithelia resulting in scar tissue
- The scar tissue narrows the airways and makes breathing difficult

Emphysema develops as a result of frequent infection, meaning phagocytes are attracted to the lungs where they release elastase - an enzyme that breaks down the elastin in the alveoli walls, to enable them to reach the surface where the bacteria are
Without adequate elastin, the alveoli cannot stretch, so they recoil and many burst
The breakdown of alveoli results in the appearance of large air spaces, reducing the surface area for gas exchange and making sufferers breathe more rapidly
As it progresses, patients become breathless and wheezy - they may need a constant supply of oxygen to stay alive

The breakdown of alveoli in emphysema reduces the surface area for gas exchange

Carbon monoxide binds irreversibly to haemoglobin, reducing the capacity of blood to carry oxygen
This puts more strain on the breathing system as breathing frequency and depth need to increase in order to get the same amount of oxygen into the blood
It also puts more strain on the circulatory system to pump the blood faster around the body and increases the risk of coronary heart disease and strokes

Nicotine narrows blood vessels so puts more strain on the circulatory system and increases blood pressure
Narrow blood vessels are more likely to become clogged with fat, including cholesterol - if this happens in the coronary artery, this causes coronary heart disease
This means the heart muscle cells do not get sufficient oxygen and so less aerobic respiration takes place
To compensate the cells respire anaerobically, producing lactic acid which cannot be removed (due to lack of blood supply)
This creates a low pH environment in the cells causing enzymes to denature and eventually, heart muscle cells will die
If enough die this can cause a heart attack
Another effect of nicotine is low birth weight in babies born to mothers who smoke during their pregnancy
- Nicotine narrows the blood vessels in the umbilical cord, which reduces the supply of oxygen and important food molecules to the fetus
- The placenta can also separate from the uterus, causing bleeding, premature birth and sometimes, miscarriage or stillbirth

Effects of Tobacco Smoke (Cambridge O Level Biology)