4.3.1.6 Human Defence System Flashcards
What are humans’ first line of defence against pathogens?
non-specific defence systems against pathogens
How do bacteria and viruses cause illnesses?
- bacteria and viruses may reproduce rapidly inside the body
- bacteria may produce poisons (toxins) that damage tissues and make us feel ill
- viruses live and reproduce inside cells, causing cell damage
Human non-specific defence systems agains pathogens:
- skin
- nose
- trachea and bronchi
- stomach
How is skin a non-specific defence system?
- acts as a physical barrier against pathogens
- it produces antimicrobial secretions (sweat and fatty acids) to kill bacteria
- good microorganisms known as skin flora compete with the bad microorganisms for space and nutrient
- produces sweat and fatty acids
How is the nose a non-specific human defence system?
- has hairs and mucus (sticky substance) which prevent particles from entering the lungs
- removal of inhaled particles through e.g. sneezing
How is the trachea and bronchi a non-specific human defence system?
- secrete mucus in order to trap pathogens
- muscle and cilia (hair-like structures) beat to waft mucus upwards so it can be swallowed
How is the stomach a non-specific human defence system?
- produces hydrochloric acid that kills any ingested pathogens (e.g. bacteria) from mucus, food or drink
- kills pathogens as hydrochloric acid has a low pH and denatures the pathogens
How are the large and small intestines non-specific human defence systems?
- rapid pH change from stomach to upper intestine
- normal flora in large intestine
How is the vagina a non-specific defence system?
- pH (slightly acidic) and normal flora of vagina
- flushing of urinary tract
What is the role of the immune system in the defence against diseases?
- if a pathogen enter the body the immune system tries to destroy the pathogen
- the specific immune system acts to destroy any pathogens which pass through the non-specific immune system to the body
- a large part of the specific immune system is white blood cells, which can act in 3 different ways: phagocytosis, producing antibodies, producing antitoxins
What are humans’ second line of defence against pathogens?
- non-specific defence systems
- involves white blood cell - phagocyte
- phagocytosis takes place
Process of phagocytosis:
- Phagocytes are attracted to any area of the body in which an infection is present
- Phagocyte (type of white blood cell) moves towards a bacterium
- The phagocyte begins to engulf the bacterium
- When the phagocyte comes into contact with pathogen, it binds to it
- The membrane of the phagocyte then surrounds the pathogen and engulfs it with the cytoplasm of the phagocyte wrapping around the bacterium - the bacterium is engulfed into the vacuole
- The bacterium is now enclosed in a vacuole inside the phagocyte
- Digestive enzymes enter the vacuole and it is killed and digested
Diagram for process of phagocytosis:
What is the third line of defence against pathogens (the immune response)?
- the third line of defence against infection is specific
- a specific white blood cell ( a lymphocyte) is activated to prevent further disease
How is producing antibodies used to defend against pathogens?
- each pathogen has an antigen on their surface, which is a structure with a specific complementary antibody which can bind to it when they come in close proximity
- lymphocytes only recognise one type of antigen
- when the lymphocyte binds to the antigen, antibodies are produced in huge quantities
- these proteins clump the pathogens together, preventing them from entering body cells and making it easier for white blood cells to find them, leaving them more vulnerable to phagocytosis
- if you become infected again with the same pathogen, the specific complementary antibodies will be produced at a faster rate
- the individual will not feel the symptoms of the illness - said to be immune
Diagram to show how antibodies work:
Diagram to show the specificity of lymphocytes to antigens:
