11.1.1

Phagocytes

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Phagocytosis

Phagocytosis is the first stage in the immune response that takes place in white blood cells called phagocytes.

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Phagocytes

  • Phagocytes include macrophages and neutrophils. They divide and differentiate from stem cells in bone marrow.
  • Phagocytes undertake phagocytosis. The steps involved in this process are:
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1) Detection of antigens

  • Foreign antigens bind to specific receptors on the cell surface of phagocytes.
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2) Engulfing the pathogen

  • The phagocyte moves towards the pathogen.
  • The phagocyte cytoplasm surrounds the pathogen and the pathogen is engulfed.
  • When the pathogen is engulfed, it is sealed into a phagosome (a vesicle) inside the cytoplasm.
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3) Digestion of the pathogen

  • Phagocytes have many organelles called lysosomes that contain proteolytic enzymes.
  • A lysosome fuses with the phagosome and releases the proteolytic enzymes into the phagosome.
  • The enzymes break down the pathogen.
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4) Presenting the antigens

  • The pathogen antigens are transported to the phagocyte cell membrane and presented on the cell surface.
  • The antigens can activate the other cells in the immune response.

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6Nucleic Acids & Protein Synthesis

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11Immunity

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