AQA AS Biology Unit 1: Lung Disease

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Lung Disease ­ Pulmonary Tuberculosis
The features of the lungs that make them so good at gas exchange also makes them
susceptible to disease.
The large volumes of air passing through the lungs may carry infectious pathogens or other
microscopic particles that cause disease.
Pulmonary Tuberculosis
Causes and Symptoms
Pulmonary tuberculosis is an infectious disease caused by the bacterium mycobacterium
The symptoms of pulmonary tuberculosis initially include a persistent cough, tiredness and
loss of appetite that leads to weight loss.
As the disease develops, fever and coughing up of blood may occur.
TB is spread through the air by droplets, released into the air when infected individuals
cough, sneeze, laugh or even talk.
Mycobacterium tuberculosis is a resistant bacterium that can survive several weeks once
the droplets have dried.
It normally takes close contact with an infected person over a period of time rather than a
brief meeting to transmit the bacteria.
TB is usually spread between family members, close friends or work colleagues, especially in
crowded and poorly ventilated conditions.
TB can also be spread from cows to humans.
Some groups are at a greater risk of contracting TB:
People in close contact with infected individuals over long periods
Work or reside in long-term care facilities where relatively large numbers of people
live close together
People from countries where TB is common
People with reduced immunity

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Course of Infection
Once mycobacterium tuberculosis has been inhaled by someone who is not immune to it,
the infection follows a particular course:
1. The bacteria grow and divide within the upper regions of the lungs where there is a
plentiful supply of oxygen
2. The body's immune system respond s and white blood cells accumulate at the site of
infection to ingest the bacteria
3.…read more

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Prevention and Control of TB
The main biological preventative measure for TB is vaccination.
All children in the UK are routinely tested for their immunity to TB.
Vaccination of those individuals who are already immune is unnecessary and dangerous.
Those without immunity are given the vaccine.
This is a weakened strain of mycobacterium bovis.
In addition to biological means of prevention, there are social and economic measures that
can be introduced to reduce the number of TB cases.…read more

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Pulmonary Fibrosis
Pulmonary fibrosis arises when scars form on the epithelium of the lungs causing them to
become irreversibly thickened.
Scar tissue is thicker and less elastic than normal lung tissue.
This means that the lungs are less able to expand and so can't hold as much air as normal ­
the tidal volume is reduced.
It's also harder to force air out of the lungs due to the loss of elasticity.…read more

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Asthma is a respiratory condition where the airways become inflamed and irritated.
The causes vary from case to case but it's usually because of an allergic reaction to
substances such as pollen and dust.
During an asthma attack, the smooth muscle lining the bronchioles contracts and a large
amount of mucus is produced.
This causes constriction of the airways, making it difficult for the sufferer to breathe
properly.…read more

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Emphysema is a lung disease caused by smoking or long term exposure to air pollution ­
foreign particles in the smoke become trapped in the alveoli.
This causes inflammation, which attracts phagocytes to the area.
The phagocytes produce an enzyme that breaks down elastin which is a protein found in
the alveoli.
Elastin is elastic which helps the alveoli return to their normal shape after inhaling and
exhaling air.…read more

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Risk Factors of Lung Disease
There are a number of specific risk factors that increase the probability of someone
suffering from lung disease.
In this content lung disease refers to chronic obstructive pulmonary disease, which includes
emphysema and chronic bronchitis.…read more


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