Body defences and the immune system
Non-specific defences
The body's first line of defence tries to stop any pathogen getting in. These defences are — they work the same way against every pathogen.
- Skin — a physical barrier; it also produces antimicrobial secretions, and forms scabs to seal cuts.
- Nose — hairs and trap particles that may contain pathogens.
- Trachea and bronchi — mucus traps pathogens, and (tiny hairs on the lining cells) waft the mucus up to the throat, where it is swallowed.
- Stomach — produces hydrochloric acid, which kills pathogens in food and drink.
Key terms
The immune system
If a pathogen gets past the non-specific defences and enters the body, the tries to destroy it. are the key cells of the immune system. They fight pathogens in three ways:
Phagocytosis
Some white blood cells, called , engulf pathogens. The phagocyte surrounds the pathogen, takes it inside, and digests it using enzymes. This is .
Phagocytosis is non-specific — phagocytes will engulf any pathogen they meet.
Key terms
Antibodies and antitoxins
Every pathogen has unique molecules on its surface called . Some white blood cells () produce — proteins that are specific to one antigen. Antibodies lock onto the antigens of that pathogen, clumping pathogens together or marking them so they can be destroyed.
Some white blood cells produce , which bind to and neutralise the toxins released by bacteria.
The first time you meet a new pathogen, it takes time to make the right antibodies, so you may become ill.
Key terms
Memory cells and immunity
After an infection, some white blood cells become . They stay in the blood and 'remember' the pathogen's antigen.
If the same pathogen enters the body again, memory cells trigger a : the right antibodies are produced much faster and in larger amounts. The pathogen is destroyed before it can make you ill — you are to that disease.