Body defences against pathogens

Pathogens are microorganisms that can cause disease. The body has defences that block or trap pathogens before they enter, and others that deal with pathogens that get past these barriers.

Barriers to pathogen entry

The skin forms a physical barrier that blocks many pathogens from entering the body.

In the breathing system, hairs in the nose and mucus help trap particles and microorganisms from the air before they reach deeper parts of the system.

Pathogens can also be swallowed in food or water. Stomach acid kills many of them before they can cause disease.

White blood cells

Some pathogens get past the body’s first barriers. White blood cells help defend the body by attacking and destroying these pathogens.

Mucociliary defence of the breathing system

The airways contain cells that trap inhaled material and move it away from the lungs. This helps stop particles and pathogens, such as disease-causing microorganisms, from reaching the gas exchange surfaces.

Goblet cells produce mucus, a sticky substance that coats the airway lining. Inhaled particles and pathogens become trapped in the mucus rather than continuing deeper into the lungs.

Ciliated cells have tiny hair-like structures called cilia on their surfaces. The cilia beat to move the mucus towards the throat, carrying the trapped material away from the lungs. This combined action of mucus and cilia is called mucociliary defence.

White blood cells

White blood cells help defend the body against pathogens, such as disease-causing bacteria and viruses. Different white blood cells defend the body in different ways.

How white blood cells attack pathogens

Some white blood cells surround and engulf a pathogen, taking it into the cell. They then digest and destroy it. This process is called phagocytosis.

Other white blood cells produce antibodies. These are proteins that bind to specific targets on pathogens, helping the body recognise and eliminate them.

Identifying white blood cells

White blood cells have a nucleus. In photomicrographs and diagrams of human blood, this distinguishes them from mature red blood cells, which do not have a nucleus.