h2 smoking

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H2 Smoking

AS Level and A Level Biology

Chapter 12Pages 150-164


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Learning outcomes

Candidates should be able to:

(e) describe the effects of tar and carcinogens in tobacco smoke on the gas exchange system;

(f) describe the signs and symptoms of lung cancer and chronic obstructive pulmonary disease

(emphysema and chronic bronchitis);

(g) describe the effects of nicotine and carbon monoxide on the cardiovascular system;

(h) explain the link between smoking and atherosclerosis, coronary heart disease and strokes;

(i) evaluate the epidemiological and experimental evidence linking cigarette smoking to diseaseand early death;

(j) discuss the difficulties in achieving a balance between preventions and cure with reference to

coronary heart disease, coronary by-pass surgery and heart transplant surgery;

(k) use the knowledge gained in this section in new situations or to solve related problems.


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Introduction

The World Health Organisation (WHO)

considers smoking to be a disease.

Each day, 1200 young boys, and as many

young girls, take up smoking.


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1. Tobacco smoke

There are over 4000 different chemicals incigarette smoke, many of which are toxic.

Tobacco smoke consists of: mainstream smoke (from the filter or mouth end),

sidestream smoke (from the burning tip).

About 85% of smoke released from smoking issidestream smoke. Many of the toxic ingredientsare in higher concentration in this smoke.


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Breathing someone elses smoke is calledpassive smoking and can be harmful.

Three main components of cigarette smoke thatcan cause damage either to the gaseousexchange or cardovascular systems are:

tarwhich settles on lining of airways in lungs and cancause obstructive lung diseases and lung cancer,

carbon monoxide forms the stable compoundcarboxyhaemoglobin, putting a strain on the heart and

damaging the lining of arteries, nicotine increases heart rate and blood pressure and

decreases oxygen supply to bodys extremities. Alsoincreases stickiness of blood platelets.


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Both carbon monoxide and nicotine

increase the risk of developing

cardiovascular disease.

Link was discovered in latter half of

twentieth century.


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2. Lung disease

Despite the filtering system of the lungs, very smallparticles (


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Severe coughing, in response to production of

mucus in lungs, can damage alveoli.

Continuous damage can lead to replacement of

thin alveolar surface with scar tissue, so

reducing surface area for diffusion.

Chronic (long-term) obstructive lung diseases

such as asthma, chronic bronchitis and

emphysema are now the most common cause of

illness and death in the UK after heart disease

and strokes.


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Chronic bronchitis

Tar in cigarette smoke stimulates goblet cells

and mucous glands to enlarge and secrete more

mucus.

It also destroys many cilia lining the epithelium

and weakens the action of those that remain.

This leads to smokers cough and thickening of

airways.


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Trapped bacteria and viruses can cause

infections such as pneumonia.

Infection then leads to linings becoming

inflamed, further narrowing the airways.

This is chronic bronchitis, characterised

by large quantities of phlegm and severecoughing.


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Emphysema

With smallerquantities of elastinin the alveolar

walls, some alveolimay burst duringexhalation. Thisreduces surface

area for gaseousexchange, i.e.emphysema.


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People with emphysema do not oxygenate their

blood very well and have rapid breathing rate.

As the disease progresses, blood vessels in

lungs become more resistant to blood flow so

blood pressure increases to compensate andright side of heart enlarges.

People with severe emphysema often need a

continuous supply of oxygen to stay alive.


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Chronic obstructive pulmonary

disease

Chronic bronchitis and emphysema often occur

together.

The term chronic obstructive pulmonarydisease refers to the overall condition which is

progressively disabling.

Only in rare cases is this reversible and can only

happen in young people if smoking is given up.


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Lung cancer

Tobacco smoke contains carcinogens.

These react with DNA in epithelial cells toproduce mutations and eventually a

malignant tumour.

The cancer can then spread (metastasis)

to other organs via the lymphatic system.


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Lung cancer takes 20-30 yearsto develop.

The most common symptomsare coughing up blood due totissue damage.

Tumours in lungs can be

located by: bronchoscopy, chest X-ray,

CT scan.

Treatments include

chemotherapy with anti-cancerdrugs or radiotherapy with X-rays.


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3. Providing the links between

smoking and lung disease

In 1912, there were

374 cases of lung

cancer, now there

are over 35 000deaths a year in the

UK from the

disease.


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Different epidemiological data link smoking and

lung diseases, including lung cancer (see pages

154-155).

Conclusions drawn from these data can be

criticised because they only show that there isan association and not a causallink. But

smoking is the common factor in all cases.

Cigarette smoking is also linked with other

cancers, i.e. mouth, oesophagus, larynx,

bladder, etc.


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Experimental evidence

Experimental evidenceshows a direct causativelink between smoking andlung cancer.

Two lines of evidenceexist: tumours similar to those in

humans develop in animalsexposed to cigarette smoke.

carcinogens have beenidentified in tar.


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4. Cardiovascular diseases

Cardiovascular diseases are degenerativediseases of the heart and circulatory system,e.g. coronary heart disease and stroke.

They are responsible for 20% of deathsworldwide and up to 50% of deaths in developedcountries.

Many factors contribute to the development ofthese diseases, i.e. they are multifactorial.Smoking is one of these risk factors.


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Atherosclerosis

Cholesterol is lipid needed for thesynthesis of vitamin D in the skin,steroid hormones in the ovaries,testes and andrenal glands andplasma membranes in all cells.

It is insoluble in water so istransported in blood plasma aslipoprotein.

There are two types: HDL remove cholesterol from

tissues and transport it to the liver

to be excreted, LDL transport cholesterol from liver

to tissues, including the arterywalls.


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The main process that leadsto cardiovascular diseases isatherosclerosis the build-

up of an atheroma whichcontains cholesterol, fibres,dead muscle cells andplatelets.

The cholesterol-richatheroma forms plaques inthe lining of arteries makingthem less elastic andrestricting the flow of blood.

The restricted blood flow canlead to thrombosis, i.e. theproduction of a thrombus(blood clot).


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Coronary heart disease

Two coronary arteries branch from the aorta to

supply all the muscles of the atria and ventricles.

Coronary heart disease is a disease of thesearteries that causes damage to or malfunction of

the heart.

It develops if the blood supply to the heart is

reduced, e.g. through atherosclerosis.


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There are three forms of coronary heart

disease:

angina pectoris the main symptom is

severe chest pain when exercising which

goes away when resting.

heart attack (myocardial infarction) mainsymptom is sudden and severe chest pain.

heart failure the heart weakens and fails to

pump efficiently.


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Stroke

A stroke occurs when an artery in the brain bursts sothat blood leaks into brain tissue (a brain haemorrhage)or when a blockage occurs in a brain artery due toatherosclerosis or a thrombus.

The brain tissue in the area supplied by the artery isstarved of oxygen and dies, i.e. cerebral infarction.

A stroke may be fatal or cause mild or severe disability.


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Global distribution of coronary

heart disease

Coronary heart disease has mainly been

confined to developedcountries.

It is considered to be a disease associated withaffluence but also a degenerative disease.

In the developingworld, where death rates frominfectious diseases is decreasing, death rates

from cardiovascular diseases is increasing.


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Death rates fromcoronary heart

disease also differ

within countries.


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Epidemiological evidence

The evidence for links between smoking andcardiovascular diseases is not as clear cut as it is forsmoking and lung cancer.

Smoking increases: the chances of both the development of atherosclerosis and

blood clotting,

blood pressure (a risk factor for stroke),

the concentration of cholesterol in blood (a risk factor forcoronary heart disease).

Smoking also increases the risk of developingcardiovascular diseases in passive smokers.


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These factors were identified in long-termepidemiological studies with large groups of

participants.

To find the reasons for the global distribution ofcoronary heart disease, the WHO set up a

multinational monitoring project, called MONICA,in 1979.

Evidence from this study pointed to the

importance ofblood pressure and bloodcholesterolas key factors in predicting whethersomeone would suffer from heart disease.


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Recent research suggests that genetic factors

are important.

Genes can affect blood cholesterol levels, blood

pressure and development of diabetes.


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The role of diet in coronary heart

disease People with high levels ofsaturatedfat and cholesterol in their

diet tend to have high blood cholesterol levels and highincidences of heart disease, e.g. Finland.

Red meat and dairy products are especially rich in saturated

fats.

Mediterranean countries also have high fat intake in theirdiets, but this is mainly unsaturatedfat. Therefore theincidence of heart disease is lower.

In France, there is a high intake of saturated fat but has oneof the lowest rates of heart disease. This suggests thatsaturated fat and cholesterol intake alone are not important.


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Prevention and cure of coronary

heart disease Reduction of the incidence and prevalence of heart disease can

occur by: taking more exercise,

giving up smoking,

decreasing intake of animal fat.

Treatment for coronary heart disease includes drugs to: lower blood pressure,

decrease the risk of blood clotting,

prevent abnormal heart rythms,

reduce the retention of fluids,

decrease blood cholesterol concentrations.

If drug treatments do not work then a coronary artery by-passoperation may be carried out.


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A complete heart transplant is the method of lastresort.

Two ways to reduce the cost of treating coronaryheart disease include: identifying and concentrating resources on those in

the population at highest risk, encouraging the population to adopt a healthy

lifestyle.

Epidemiological evidence suggests that bettermaternal nutrition better protects against heartdisease.


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