description about phagocytosis

1. Dr.TULIKA CHAUDHARY

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

5. *Polymorphonuclear
neutrophils helps in
engulfment of foreign
particles or bacteria
and kill them by
phagocytosis.

6.  Attachment stage (opsonisation)
 Engulfment stage
 Secretion stage (degranulation)
 Killing or degradation stage

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.

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.

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.

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.