(5) The ingesting of pathogens by white blood cells - action of phagocytes

White cells can surround 'foreign' invasive microorganisms and break them up, effectively digesting them.

The white blood cells that do this are called phagocytes and the process is called phagocytosis.

Phagocytes are made and stored in the bone marrow - the soft tissue at the centre of bones.

When an infection happens more phagocytes are released and travel through the blood to the point where the pathogen (e.g. bacteria) has entered the body and the diagram shows what happens next.

1. The phagocyte detects the presence of pathogens and moves towards them e.g. move towards a bacterium.

2. Phagocytes have a flexible membrane that changes shape and pushes out to surround one or more of the pathogens.

3. The pathogens then, via the flexible membrane, become completely enclosed (trapped) in the cytoplasm of the phagocyte cell (creating a vacuole) and can then be 'digested'.

4. The pathogen (e.g. bacterium) is killed and enzymes in the cytoplasm of the phagocyte break the pathogens down and the products absorbed into the phagocyte's cytoplasm.

Phagocytes can leave the bloodstream and squeeze through capillaries and enter tissues attacked by some invasive pathogen infection.

The phagocytes move to the pathogens (or toxins) and ingest them.