Phagocytic cells in brain -
Ans. is 'c' i.e., MicrogliaMicroglia are the major phagocytic cells in the brain.Phagocvtosis Phagocytosis and release of enzymes by neutrophils and macrophages are responsible for eliminating injurious agents.o Phagocytosis involves the following three steps.1. Recognition and attachmentPhagocytosis of microbes and dead cells is initiated by recognition of paicles by receptors expressed on leukocyte surface.These receptors are Mannose receptors and scavenger receptors.These receptors bind a variety of microbes.2. EnglulfmentBinding of a paicle to phagocytic leukocyte receptors initiates the process of active phagocytosis of the paicles.During engulment, extension of the cytoplasm, i.e., pseudopods flow around the paicle to be engulfed. Eventually, this results in complete enclosure of the paicle within a phagosome created by the plasma membrane.Membrane of this phagocytic vacuole (Phagosome) fuses with the membrane of lysosome to form phagolysosome resulting in discharge of lysosomal granule's content into phagosome.During this process neutrophils and macrophages become progressively degranulated.Phagocytosis is dependent on polymerization of actin (similar to chemotoxis that is also dependent on polymerisation of actin).3. Killing and degradationKillingMicrobial killing is accomplished largely by oxygen-depending mechanism, i.e., due to generation of reactive oxygen species.The generation of reactive oxygen species is due to rapid activation on an oxidase - NADPH oxidase. Reactive oxygen species cause membrane damage, cytoskeletal damage and DNA damage.Bacterial killing can also occur by oxygen-independent mechanisms, through action of substances in leukocyte granules -3 Bacterial permeability increasign protein (BPI), lysozyme, lactoferrin, major basic protein and defensin.DegradationAfter killing, acid hydrolases, which are normally stored in lysosomes, degrade the microbes within phagolysosome.
Oligodendrocytes
Macrophages
Microglia
Astrocytes