Non-specific Defence Systems

The body’s first line of defence works together to prevent 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 secretes an oily substance called sebum that can kill pathogens.

When the skin is damaged, it forms scabs to prevent pathogens from entering the body.

As pathogens cannot penetrate our skin, they must find entry points, such as the mouth or nose. However, these openings have their own defence systems to protect us from infections.

  • For example, tears contain enzymes called lysozymes that protect against bacteria


The nose produces mucus that traps pathogens, preventing them from entering the trachea and our lungs. When we blow our nose, both the mucus and the trapped pathogens are expelled.

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

  • Goblet cells produce mucus that 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 move rhythmically, transporting the mucus and trapped pathogens upward 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 that lowers its pH, making the environment acidic. However, this acidic environment also kills pathogens before they can move further into the digestive system.

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