3. Phagocytosis is defined as the process of
engulfment of solid particulate material by
the cell.
Phagocytosis is chiefly a defensive reaction against infection
and invasion of the body by foreign substances (antigens).
4. The white blood cells protects the body by
ingesting harmful foreign particles, bacteria and
dead cells.
These cells helps in performing the process of
phagocytosis and known as Phagocytes.
There are 2 main type of phagocytic cells:
Neutrophils
macrophages
8. Opsonization refers to the process of
coating of bacteria by opsinins by which
bacteria become tasty to the phagocytes.
IgG opsonin and its corresponding
receptor on the surface of polymorphs and
monocytes is Fc fragment of
immunoglobulin.
C3b opsonin fragment of complement
and corresponding receptor for C3b on
the surface of phagocytic cells.
9.
10. The opsonized particle bound to the
surface of phagocyte is ready to be
engulfed.
This is done by formation of pseudopods
around the particle, enveloping it in a
phagocytic vacuole.
Pseudopods meet each other on opposite
side and fuse, this create an enclosed
chamber with the engulfed material.
11.
12. Once the bacteria is engulfed, the
lysosomes pour their enzymes into the
vesicles and also in interstitial space.
This process is called degranulation.
There are large number of enzymes
geared up for digesting bacteria.
Lysosomes of macrophages contain
lipases which digest the thick lipid
membranes possesed by certain bacteria.
13.
14. The neutrophils and macrophages contain
bactericidal agents which can kill most of
the bacteria.
The microorganism after killed by
antibacterial sustances are degraded by
hydrolytic enzymes,this mechanism fails to
kill & degrade some bacteria like tubercle
bacilli.
The antimicrobial agents act by either of
the following mechanism:
a) Oxygen dependent mechanism
15. It is important mechanism of microbicidal
killing is by the production of reactive oxygen
metabolites.
Increased oxygen consumption with an
increased formation of ROS- respiratory
burst
Increase in the activity of NADPH
phagosome oxidase.
NADPH- oxidase present in the cell
membrane of phagosome reduce oxygen to
superoxide ion.
16. Some agents released from the granules
of phagocytic cells do not require oxygen
for bactericidal activity.
These include lysosomal hydrolases ,
permeability increasing factors , defensins
and cationic proteins.