The body’s first line of defence
Your body has a two-line defence system against pathogens (germs) that make you sick. Pathogens include bacteria, viruses, toxins, parasites and fungi.
Boy with grazed elbow
Microorganisms that live all over your skin can’t get through your skin unless it’s broken.
The first line of defence (or outside defence system) includes physical and chemical barriers that are always ready and prepared to defend the body from infection. These include your skin, tears, mucus, cilia, stomach acid, urine flow, ‘friendly’ bacteria and white blood cells called neutrophils.
Pathogenic (disease-causing) microorganisms must make it past this first line of defence. If this defence is broken, the second line of defence within your body is activated.
Skin The skin is the largest organ of your body. It acts as a barrier between invaders (pathogens) and your body. Skin forms a waterproof mechanical barrier. Microorganisms that live all over your skin can’t get through your skin unless it’s broken.
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Dr Joanna Kirman talks about snot. Although it seems disgusting, we learn snot is actually a good thing and is one of our weapons to fight disease. It is produced to clear the airways of infectious diseases and anything else that should not be there.
Tears, mucus and saliva Your nose, mouth and eyes are obvious entry points for pathogens. However, tears, mucus and saliva contain an enzyme that breaks down the cell wall of many bacteria. Those that are not killed immediately are trapped in mucus and swallowed. Special cells line and protect the nose, throat and other passages within your body. The inner lining of your gut and lungs also produces mucus to trap invading pathogens.
Cilia Very fine hairs (cilia) lining your windpipe move mucus and trapped particles away from your lungs. Particles can be bacteria or material such as dust or smoke.
Stomach acid Stomach acid kills bacteria and parasites that have been swallowed.
Urine flow Your urine flow flushes out pathogens from the bladder area.
Crying child
Skin, tears and mucus are part of the first line of defence in fighting infection. They help to protect us against invading pathogens.
‘Friendly’ (beneficial) bacteria You have beneficial bacteria growing on your skin, in your bowel and other places in the body (such as the mouth and the gut) that stop other harmful bacteria from taking over.
Neutrophils These are white blood cells that can find, kill and ingest pathogens seeking an entrance into the body.
You may now like to read this article The body's second line of defence.
The body’s defence
Professor Graham Le Gros from the Malaghan Institute explains the body’s defence system. He talks about the first line of defence, which involves the skin barrier. He then talks about how pathogens can get behind this barrier into deeper tissues. This calls for the immune system – cells designed to hunt down and kill the worst bugs that we face.
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