Pathogens and Infection

Biology Unit 4

Pathogens and Infection

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Biology Unit 4
Revision Notes
Topic 6: Infection, Immunity and Forensics
10. Describe the major routes pathogens may take
when entering the body and explain the role of
barriers in protecting the body from infection,
including the roles of skin, stomach acid, gut and skin
Pathogens enter the body through areas not covered by skin: nose, mouth, gas exchange surfaces,
the eyes, gastrointestinal tract and genital tract. The entry of micro-organisms through wounds is
also a major cause of infections.
Eyes ­ tears contain the enzyme lysozyme which helps to digest microbes
Respiratory tract ­ contains mucus which traps bacteria. The mucus is then swallowed
and passed into the digestive system
Gastrointestinal tract ­ acid in the stomach helps to protect against any microbes
which are eaten. In addition the gut has its own bacteria. These compete with pathogens for
food and space which helps to protect us. The harmless bacteria also excrete lactic acid which
deters pathogens.
Skin ­ the skin is a tough barrier and usually only allows pathogens to enter if it is cut. As an
additional line of defence the skin has its own microbes- skin flora. These live naturally on
the skin and out-compete pathogens. Sebum is an oily fluid which is made by the skin and can
also kill microbes.
Ways in which pathogens enter the body
Name How the body barriers prevent infection Example
Vector (organism that Blood clotting mechanism Malaria, Dengue, Yellow Fever
transmits infection) Skin in tough and contains Keratin and
Formites (inanimate The skin, natural skin flora, vomiting Staphylococcus infections
objects carry
Direct contact (skin Lysozymes, defensive secretions, mucus, Impetigo, gonorrhoea, syphilis
disease/sexual contact) skin flora
Inhalation (coughing, Mucus, vomiting, lysozymes, cilia Influenza, measles, TB
sneezing, talking)
Ingestion Vomiting, mucus, saliva Diarrhoea, hepatitis A,
(contaminated food) salmonella
Inoculation (break in Skin, antibodies, immune response, blood Hepatitis B, HIV, rabies,
the skin) clotting tetanus
Text Book: p. 92 ­ 95


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