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Human Biology (Year 12) - Defence Against Pathogens

Ben Whitten

What is a phagocyte?

A phagocyte is a cell that can engulf and digest micro-organisms and cell debris by the process of phagocytosis, and includes leucocytes and macrophages.

Leucocytes are also known as white blood cells. They can travel to blood capillaries, and also leave them to migrate through tissue to places of infection/injury; some types of leucocytes secrete bacteria-killing substances whilst others engulf live bacteria and digest it.

Macrophages are large phagocytic cells that develop from some leucocytes. Some are wandering

cells which "look" for pathogens, whilst others are fixed in place and let pathogens find them. They either engulf and digest micro-organisms or release substances that destroy them.

What is the process of phagocytosis?
  1. A phagocyte is attracted to the foreign antigen in question and proceeds to engulf it; it changes shape so that it completely encloses the bacterium/antigen

  2. A vacuole forms inside the phagocytic cell, and a lysosome binds to the vacuole and releases digestive enzymes (lysosomes are a cell organelle which contain destructive enzymes, and upon the release of these enzymes, the bacterium is destroyed)

  3. This actively breaks down the microbe/antigen, leaving soluble debris (harmless) as a result

  4. The debris exits the phagocyte via exocytosis (active transport)

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