Effects of Tobacco Smoke (Cambridge (CIE) O Level Biology): Revision Note

Effects of Tobacco Smoke

Chemicals in 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

• 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

• 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 diagram

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

Carbon monoxide

• 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

• 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

Smoking & Lung Cancer: Is There a Link

• The majority of cases of lung cancer are caused by smoking

Graph showing correlation between numbers of adults who smoke and lung cancer rates over time

• Note that as the general trend shows that as the numbers of adults who smoke decreases, so does the lung cancer rates a few years later (as cancer takes some time to develop)

• The trend in the rate of developing lung cancer for women has been increasing, while in men it is decreasing

• This is because numbers of female smokers – unlike men – continued to increase in the 1950s and 1960s before starting to fall

• As cancer takes some years to develop, a fall in female rates of lung cancer is likely to occur later