Causes of Disease - AQA - Unit 1
- Created by: Eleanor
- Created on: 21-03-13 08:42
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- Causes of Disease
- Disease can be described as certain symptoms: either mental, physical or both
- Disease suggests a malfunction of body or mind which does not lead to good health
- For a microorganism to be considered a pathogen it must:
- 1) gain entry to the host
- 2) Colonise the hosts tissues
- 3) Resist the defences of the host
- 4) Cause damage to the hosts tissues
- Pathogens include bacteria, viruses and fungi
- When a pathogen is transferred from one host to another then it is called transmission
- Most commonly pathogens penetrate one of the bodies links to the external environment
- An example of an interface is the skin, which acts as a barrier and forms a continuous layer
- When the skin is broken though (e.g. a cut) it allows an area for a pathogen to enter.
- At areas with contact to the environment, it is often thin, moist, with a large surface area and well supplied with blood vessels
- Although this leads to efficient exchange of materials, it is perfect entry for a pathogen
- Most common points of entry are:
- Gas-exchange system
- These types of pathogens can be inhaled and spread through air
- Pathogens that cause influenza, bronchitis and tuberculosis infect this way
- Digestive System
- Food and water may carry pathogens into the stomach and small intestine
- Cholera and typhoid causing pathogens enter the body this way
- Gas-exchange system
- An example of an interface is the skin, which acts as a barrier and forms a continuous layer
- Natural defences against pathogens are present in the body
- A mucous layer that covers exchange surfaces and forms a thick sticky barrier
- The production of enzymes that break down the pathogens
- The production of stomach acid, with a pH to kill pathogens
- Pathogens affect the body in two main ways
- Damaging host tissues
- Viruses prevent the synthesis of DNA, RNA and proteins by the host cells
- Many pathogens break down the membranes of host cells
- Producing toxins
- Most pathogens do this, whether in the blood stream or inside the host cells
- Damaging host tissues
- Disease can be described as certain symptoms: either mental, physical or both
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