Human defence responses

Humans, like many other animals, have two main forms of defence against pathogens: non-specific and specific defences.

The non-specific defences are the body's first line of defence, aiming to prevent pathogens from entering.

1. Skin: The skin acts as a physical barrier, stopping pathogens from entering the body. It also produces antimicrobial secretions that help destroy pathogens.

2. Nose: The nose has hairs and produces mucus to trap pathogens, preventing them from entering the respiratory system.

3. Trachea and Bronchi: These airways produce mucus to trap pathogens. They also contain tiny hair-like structures called cilia that move the mucus (and trapped pathogens) up the trachea to the throat, where it can be swallowed.

4. Stomach: The stomach produces acid, which destroys pathogens that have been swallowed.

Specific defence responses

If pathogens manage to enter the body, the immune system acts as the body's second line of defence. This system is made up of white blood cells, which play a vital role in fighting infections in three main ways:

1. Phagocytosis:

   • Some white blood cells can ingest and destroy pathogens through a process called phagocytosis. This involves the white blood cell engulfing the pathogen and breaking it down. Phagocytosis is a slower process, as each pathogen must be targeted individually.

2. Antibody Production:

   • Other white blood cells produce antibodies, which are specific proteins designed to bind to pathogens.

   • Antibodies attach to unique sites on pathogens called antigens. Each antibody is specific to a particular antigen, meaning it targets only one type of pathogen.

   • Once bound, antibodies help destroy the pathogen. If a person is exposed to the same pathogen again, the immune system can produce these antibodies more rapidly, preventing reinfection and providing immunity against the disease.

3. Antitoxin Production:

   • Certain white blood cells produce antitoxins, which neutralise toxins released by bacteria, preventing them from harming the body.