Our internal defences

Table of Contents

1. Introduction
2. The immune system – three lines of defence
   1. First line of defence – non-specific barriers
   2. Second line of defence – leucocytes (white blood cells)
   3. Third line of defence – the specific immune response
3. Specific defence – the role of lymphoid tissue and lymphocytes
4. Specific defence – the body's battalion of cells
5. The specific immune response – when the body declares war!
6. Primary and secondary immunity
   1. Types of immunity
7. Vaccines
8. The role of antibiotics and antivirals
9. Assessment task: Investigation

1. Additional resources:
   1. Glossary
   2. Print content

First line of defence – non-specific barriers

These are a combination of physical and chemical barriers that prevent all types of foreign agents from penetrating the outer layer of the body. No specific foreign agent is targeted at this level.

The barriers are:

The skin – provides an impervious barrier to pathogens.

Mucous membranes – line the entrances to the body such as in the respiratory tract entrances. Mucus produced by these membranes traps foreign particles and directs them out of the body.

Hairs and cilia – (nasal hairs) trap dust and dirt; (microscopic cilia) line some mucous membranes and direct foreign particles out of the body.

Gastric juice, vaginal secretions and urine – acidic fluids that have a protective function.

Tears, sweat and saliva – body fluids which possess some anti-bacterial properties.

Cerumen (ear wax) – produced in the ear canal and protects the canal by trapping dirt and dust particles.

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