Explain How Microorganisms Enter The Body

Biology Unit 1 – Section 3.1.1
Microorganisms as Pathogens
To be considered a pathogen it must:
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Gain entry
Colonise the tissues
Resist the defences
Cause damage to the tissues

Pathogens include bacteria, viruses and fungi

How do microorganisms enter the body
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Many pathogens enter through the gas exchange system (including ones that cause flu and
TB)
Food and water can carry pathogens into the stomach and intestines via the mouth and into the digestive system (including ones that cause cholera)

Preventing pathogens entering
 Mucous layer that covers the exchange surfaces and forms a thick sticky barrier that is difficult to penetrate
 Enzymes that break down pathogens
 Stomach acid which kills pathogens
Pulmonary Fibrosis
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Caused by scars forming on the epithelium of the lungs
Thickens the lung epithelium irreversibly

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Diffusion of oxygen into the blood is less efficient as diffusion pathway is longer
The volume of air the lungs can contain is also reduced
Reduced elasticity so difficulty ventilating the lungs (getting air in and out)

Effects of fibrosis
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Shortness of breath especially when exercising – due to less oxygen being able to diffuse into the blood
Chronic dry cough – because the fibrous tissue obstructs the airway
Pain and discomfort in the chest – due to pressure and damage from the mass of fibrous tissue
Weakness and fatigue – due to the reduced intake of oxygen into the blood so less available for respiration

Asthma
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Localised allergic reaction
Caused by the release of histamine when an allergen such as pollen is detected

Histamine has the following effects:
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The lining of the airways becomes inflamed
The lining cells (epithelial cells) secrete more mucus than usual
Fluid leaves the capillaries and enters the airways
The muscle surrounding the bronchioles contracts and constricts the airways

Effects of Asthma