Body defences

• First lines of defence against pathogens stop them coming into the body.
• The first lines of defence are general.
• They are both physical and chemical.
• The first lines of defence are: the skin, nose , trachea and bronchi and the stomach.
• When the skin in broken the platelets in the blood will try to clot the wound.
• The scab stops the pathogens entering the body.
• Eye lashes will prevent dust and other micro-organisms going in your eyes.
• The hairs in the nose trap dust and other pathogens so they don’t enter the body.
• Ciliated cells are found in the trachea and their job is to move mucus and pathogens upwards toward the throat.
• Goblet cells create mucus.
• Mucus is a physical barrier.
• The stomach produces hydrochloric acid to fight pathogens.
• the hydrochloric acid is a chemical barrier.
• The hydrochloric acid has a pH2 which is strong enough to kill bacteria.
• If the pathogens get past the first line of defence they can cause infection.
• The body has a second line of defence which is called the immune system.
• the type of blood cells that fight off disease are white blood cells.
• There are two different white blood cells which are phagocytes and lymphocytes.
• what a phagocyte does to kill a pathogen is:

  -it will engulf.

  -ingest.

  -digest

  -Finally, destroy.
• Phagocytes are non-specific.
• The protein on the surface of pathogens are called antigens.
• Lymphocytes will recognise the antigens on the surface of a pathogen.
• ‘Foreign to the body’ means that it is new to the body.
• In response to antigens lymphocytes will produce antibodies.
• It takes a lymphocyte 2-3 days to do this.
• During those days you will feel ill.
• Antibodies will lock onto the antigens on the pathogen and they will clump together.
• As a result of this, it is easier for the phagocytes to engulf.
• Some pathogens produce toxins which make you feel ill.
• Lymphocytes will produce anti-toxins in response to this.
• The anti-toxins produced by the lymphocytes will neutralise the toxins.
• Lymphocytes are specific.
• When a lymphocyte recognises an antigen, they will clone themselves to make enough anti-bodies to destroy the pathogens.
• Memory cells are created and then remain in the blood stream and if they encounter the same pathogen again they will quickly respond.
• When memory cells are created you are then said to be immune.