Your body has a two-line defence system against pathogens (germs) that make you sick. Pathogens include bacteria, viruses, toxins, parasites and fungi.
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.
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.
‘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.
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Activity ideas
Making snot – get students hooked into ideas about immunity by making fake snot. Students discover what snot is and how it is an important part of the body’s defence against infection.
The wars within – a great introduction to the immune system
Literacy in immunology – provides a cross-curricular opportunity for your students as they use their developing knowledge of immunology to make mind maps and to write poems and stories.
Curious to see how all of this fits together? Check out the Fighting infection – the immune system unit plan.
See the Viruses and the immune system curated collection – it explores viruses and how our immune system fights them. Sign in to make this collection part of your private collection. Click on the copy icon, and then you can add additional content, notes and share and collaborate with others.
