Prepared by Reem Aldossari THE GENERAL VISCRA OF THE RAT Definition of Fixation In the fields of histology pathology and cell biology fixation is a chemical process by which ID: 284581
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Slide1
Fixation and Fixative
Prepared by : Reem AldossariSlide2
THE GENERAL VISCRA OF THE RATSlide3
Definition of Fixation
In the fields of
histology
,
pathology
, and
cell biology
,
fixation
is a
chemical process
by which
biological tissues
are
preserved
from
decay
, either through
autolysis
or
putrefaction
.
Fixation
terminates
any
ongoing biochemical reactions
, and may also increases the
mechanical strength
or
stability
of the treated tissues.Slide4
Purpose of fixation
The purpose of fixation is to preserve a sample of biological material (
tissue
or
cells
) as close to its natural state as possible in the process of preparing tissue for examination. To achieve this several conditions must usually be met.
The aims of fixation are
:
Prevent postmortem (PM) degeneration
Prevent autolysis. It is effective against hydrolytic enzymes
Stop the bacterial effect
Harden the tissues, as fixation causes coagulation of proteins
Fixation has a
mordanting
effect, facilitating subsequent staining of tissues.Slide5
Features of fixatives
First
, a fixative usually acts to
disable intrinsic
biomolecules
– particularly
proteolytic
enzymes
– which would otherwise
digest
or
damage
the sample.
Second
, a fixative will typically
protect
a sample from
extrinsic damage
. Fixatives are toxic to most common microorganisms (
bacteria in particular
) which might
exist
in a
tissue sample
or which
might otherwise
colonise
the fixed tissue
.
Finally
, fixatives often alter the cells or tissues on a
molecular level
to increase their
mechanical strength
or
stability
.
This increased
strength
and
rigidity
can help preserve the
morphology
(shape and structure) of the sample as it is processed for further analysis such as
Nuclear
Morphometry
System
.Slide6
Characteristics of a good fixative
It must kill the cell quickly without shrinkage or swelling
It must penetrate the tissue rapidly
It must inhibit bacterial decay and autolysis
Harden the tissue and render it insensitive to subsequent treatment as staining
It should allow tissue to be stored for long time
It should be simple to prepare and economical is use.Slide7
Preparation of fixatives:
Neutral buffered formalin 10%:
Tap water 900 ml
formalin (40%=100%) 100ml Slide8
Thank you
for your attention