Non-specific Defence Systems

The first line of defence of the body works together to stop pathogens from entering. As they do not target specific types of pathogens, they are called non-specific defence systems. These defence systems are made up of physical barriers and chemical defences.

Let’s look at four main parts:

  • The skin
  • The nose
  • The trachea and bronchi
  • The stomach


The skin is a protective layer that covers the body. It acts as a physical barrier, to prevent infections from pathogens. The skin also secretes an oily substance called sebum, which can kill pathogens.

If the skin is damaged, it can stop pathogens from entering the body by forming scabs.

As pathogens cannot get past our skin, they must enter through openings. such as the mouth or nose. Although these openings have developed their own defence systems that protect us from infection.

  • For example, tears contain lysozymes, which are enzymes that provide protection against bacteria


The nose produces mucus which traps pathogens before they pass through to the trachea and into our lungs. When we blow our nose, the mucus is expelled, along with the trapped pathogens.

Hairs in the nose act as a natural filter that prevents dust, pollen, spores, viruses and bacteria from passing through.

  • Goblet cells produce mucus, which traps dust and pathogens
  • Basal cells can divide and differentiate into specialised cells

Trachea and bronchi

The trachea, bronchi and bronchioles are covered in a layer of mucus, which traps pathogens.

Microscopic hair-like structures called cilia line the trachea. They rhythmically move, which transports the mucus and trapped pathogens upwards, towards the back of the throat. Once it reaches the throat, it can be swallowed into the stomach, where it is digested. This prevents mucus from building up.

  • Goblet cells produce and secrete mucus


The stomach contains hydrochloric acid, which brings down the pH of the stomach, making it acidic. However, it also kills pathogens before they pass further into the digestive system.