Phagocytes
Biology: Cambridge International A Level, topic 11.1.1
Phagocytosis
Phagocytosis is the first stage in the immune response that takes place in white blood cells called phagocytes.
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:
1) Detection of antigens
- Foreign antigens bind to specific receptors on the cell surface of phagocytes.
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.
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.
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.
Test yourself on Phagocytes
What are the steps involved in phagocytosis?
Which of the following statements about phagocytosis?
What structure is the pathogen sealed into when it is engulfed?