Phagocytosis
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Phagocytosis is the process by which phagocytes engulf and destroy foreign particles. The key steps are: 1) margination and diapedesis bring phagocytes to the infection site, 2) chemotaxis guides them to pathogens, 3) opsonins coat pathogens for attachment to phagocytes, 4) pseudopods engulf the pathogen into a phagosome, 5) the phagosome fuses with lysosomes to form a phagolysosome, where 6) lysosomal enzymes degrade the pathogen.
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Phagocytosis
- 2. Scheme • Definition • Phagocyte – cell types • Steps of phagocytosis • Summary
- 3. Phagocytosis • Phagein = "to devour", kytos = "cell“, osis = “process” (from Ancient Greek) • Phagocytosis is the process of engulfment and destruction of solid particles such as bacteria, dead tissue and foreign particles by the cells.
- 4. Phagocytes • The cells performing phagocytosis are called phagocytes. The cell types are • Neutrophils • Monocytes and • Macrophages
- 5. Steps 1. Margination 2. Diapedesis 3. Chemotaxis 4. Opsonization → attachment stage 5. Engulfment stage 6. Secretion (degranulation) stage 7. Degradation stage
- 6. Margination
- 7. Diapedesis
- 8. Chemotaxis
- 9. Chemotaxis Potent chemotactic substances or chemokines are • Leukotriene B4 (LT-B4) • C5a, C3a • Cytokines
- 10. • Opsonization refers to the process of coating of bacteria by the opsonins. • The opsonin coated bacteria gets attached to the surface of phagocyte through the opsonin receptors. • The principal opsonins are IgG opsonin and C3b opsonin. Opsonization → Attachment stage
- 13. Degranulation stage • Release of lysosomal enzymes into the vesicles
- 14. Degradation stage • Oxygen dependent bactericidal mechanism mediated by oxidizing agents. • Oxygen independent bactericidal mechanism mediated by lysosomal enzymes.
- 16. SUMMARY 1. Margination 2. Diapedesis 3. Chemotaxis 4. Opsonization → attachment stage 5. Engulfment stage 6. Secretion (degranulation) stage 7. Degradation stage
- 17. THANK YOU
- 19. Engulfment • Formation of cytoplasmic pseudopods by the phagocytes around the bacteria. • The bacteria is endocytosed and is contained in a vesicle thus forming a phagosome • The phagosome fuses with nearby lysosome to form phagolysosome.
Editor's Notes
- is the process by which a cell—often a phagocyte or a protist—engulfs a solid particle to form an internal vesicleknown as a phagosome Phagocytosis was first noted by Canadian physician William Osler,[1] and later studied by Élie Metchnikoff.
- EOSINOPHILS, PLATELETS – MILDLY PHAGOCYTIC
- THE SUBST K/A CHEMOKINES RELEASED BY THE INJURED TISSUE CELLS ATTRACT THE PHAGOCYTES TOWARDS THEM THEREBY INCREASING THE CONCENTRATION OF PHAGOCYTES IN THE AREA OF TISSUE DAMAGE
- Chemo = chemical; Taxis = a motion or orientation of a cell, organism, or part in response to an external stimulus After extravasating from the blood, leukocytes migrate toward sites of infection or injury along a chemical gradient by a process called chemotaxis
- Draw and show – similar to next pic – without pseudopodia NOTE Opsonization – is only the attachment of opsin . Attachment of opsonin coated bacteria to the phagocyte is attachment stage
- Fig showing magnified surface of a neutrophil
- Release of lysosomal enzymes into the vesicles and in the interstitial space
- In the next class, we ll see what happens to the bacterial breakdown products or antigens – humoral n cell mediated immunity
- PHAGOC PIC FROM DV BOOK