causes of diseases. causes of disease disease is a change that disrupts homeostasis in the body....
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Causes of Diseases
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Causes of Disease• Disease is a change that disrupts
homeostasis in the body.• Disease-producing agents such
as bacteria, protozoans, fungi, viruses and other parasites are called pathogens.
• The main sources of pathogens are soil, contaminated water, and infected people or animals.
• Any disease caused by the presence of pathogens in the body is called an infectious disease.
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Live WormIn patient’s eye
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Causes of Disease• One-half of all human diseases are
infectious.• Not all diseases are caused by
pathogens.1. inherited disease: sickle cell
anemia2. body aging (wear and tear):
osteoarthritis• Pathogens can be transmitted in 4 main
ways:1. direct contact: STD’s and influenza 2. by an object: food poisoning3. through the air: sneezing4. intermediate organisms (vectors):
malaria (spread by mosquitoes)
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Causes of Disease
• Endemic diseases: diseases that are constantly present in a population like a cold.
• Epidemic: occurs when many people in a given area are afflicted with the same disease in a short period of time. (polio in the 1950’s)
• Carriers are people who harbor a disease without showing any signs, yet they can pass the disease on to others.
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Procedure to establish cause of disease
Koch’s postulates:1. pathogen must be found in host2. pathogen must be isolated and
grown in a pure culture3. pathogen from the pure culture is
placed in a healthy host (ex: rat)4. pathogen must then be isolated
from the new host and be shown to be the original pathogen
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Procedure to establish cause of diseaseExceptions to Koch’s
postulates:1. some organisms have
never successfully grown in an artificial medium (syphilis and leprosy)
2. viral pathogens cannot be cultured using this method
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Interesting Fact
When you sneeze, all bodily functions stop, even your heart.