TISSUE PRESERVATION IN HISTOLOGY
Preservation – the process of keeping the histological tissues’ integrity to avoid deterioration processes
like putrefaction and autolysis
Preservation can be done through various processes: physical (heating, freezing, and dehydration)
chemical (Fixation)
Fixation- The process of using chemical substance to preserve tissues to stop post mortem changes by
preserving the structures, shape, relationship and constituent of tissues and cells in as life like manner as
possible.
For good fixation;
i) Structures to be demonstrated must be taken born in mind.
ii) Tissues must be fixed as soon as possible.
iii) Amount of fixatives must be 15-20 times the size of the tissue.
Fixatives
Fixatives- chemical solutions used in preservation of tissues
Several fixatives are available and their choice depends on following factors
The type of tissue.
Urgency of investigation
Tissue structures required for demonstration and its side effects both to tissue and user.
Type of straining procedure
,Qualities of a good fixative:
1. It must kill the tissue cells quickly (to avoid further metabolism).
2. Must inhibit autolysis by inactivating enzymes.
3. Must stop Putrefaction (anti-bacterial).
4. Must render soluble substances of the cell insoluble.
5. Must penetrate the cell quickly and evenly.
6. Must harden the tissue and enable easy manipulation of Sgt tissue.
7. Must alter to varying degrees the refractive indices of different cell structures so that they are
made visible due to differentiation.
8. It must fortify the tissue against the harsh effects the solution used during processing.
9. It must have a good effect on strain.
10. Easy to prepare and not expensive in terms of cost
, Effects of fixatives:
a) Precipitation: Fixatives make soluble substances of the cells and tissues insoluble by precipitating
or coagulating the soluble proteins; this will it hard and therefore allow manipulation of soft
tissues
b) Inactivation of enzymes: Enzymes bring about metabolic activities within the cells and this may
interfere with the characteristics of the tissue structures, fixatives are therefore used to inactivate
them. The importance of fixation is to make sure that there is no change that takes place after
removal or death of tissue hence the need to stop the action of enzymes. When the cells die the
lysosomes rapture thus releasing lytic enzymes that digest the surrounding tissue, inactivation of
enzymes is important to avoid such effects.
c) Anti- bacterial: Like the enzymes bacteria can cause distortion of the tissue structures resulting of
the rotting of tissue. Bacteria that may be present as commensals, from the environment or may
have brought about disease may continue multiplying bringing certain changes in the tissue. The
fixatives have the ability to kill such bacterial cells.
d) Increase of refractive index: Certain fixatives increase or raise the refractive indices. This will allow
the various tissue structures to be clearly seen during microscopic examination.
e) Introduction of pigments: Certain fixatives when used can impart unwanted pigments onto
tissues; this may mask the tissue structures to be examined microscopically. The pigment could
be oxides as a result of chemical reactions between the fixatives and chemical constituents of
tissue or due to the colour of the fixative used.
f) Health hazards: Some fixatives can bring about harmful effects to the user. Formaldehyde for
example when handled carelessly may cause sinusitis and dermatitis, while Osmic acid fumes may
result in blindness if in contact with eye tissue.
g) Swelling: Some fixatives may make the tissue swell that may be mistaken to be an abnormality
during examination of tissue.
h) Shrinkage: A large number of tissues may shrink the tissue to an extent that wrong diagnosis may
be given, the tissue may be very normal but due to its shrunken state it look abnormal.
i) Mordanting effect: Certain fixatives will give improved preservation and staining of some tissue
structures, such fixatives may be used as secondary or after initial fixation in another fixative.
No fixative can have all the qualities hence need to have knowledge on several fixatives for proper
preservation in different histological tissues
Preservation – the process of keeping the histological tissues’ integrity to avoid deterioration processes
like putrefaction and autolysis
Preservation can be done through various processes: physical (heating, freezing, and dehydration)
chemical (Fixation)
Fixation- The process of using chemical substance to preserve tissues to stop post mortem changes by
preserving the structures, shape, relationship and constituent of tissues and cells in as life like manner as
possible.
For good fixation;
i) Structures to be demonstrated must be taken born in mind.
ii) Tissues must be fixed as soon as possible.
iii) Amount of fixatives must be 15-20 times the size of the tissue.
Fixatives
Fixatives- chemical solutions used in preservation of tissues
Several fixatives are available and their choice depends on following factors
The type of tissue.
Urgency of investigation
Tissue structures required for demonstration and its side effects both to tissue and user.
Type of straining procedure
,Qualities of a good fixative:
1. It must kill the tissue cells quickly (to avoid further metabolism).
2. Must inhibit autolysis by inactivating enzymes.
3. Must stop Putrefaction (anti-bacterial).
4. Must render soluble substances of the cell insoluble.
5. Must penetrate the cell quickly and evenly.
6. Must harden the tissue and enable easy manipulation of Sgt tissue.
7. Must alter to varying degrees the refractive indices of different cell structures so that they are
made visible due to differentiation.
8. It must fortify the tissue against the harsh effects the solution used during processing.
9. It must have a good effect on strain.
10. Easy to prepare and not expensive in terms of cost
, Effects of fixatives:
a) Precipitation: Fixatives make soluble substances of the cells and tissues insoluble by precipitating
or coagulating the soluble proteins; this will it hard and therefore allow manipulation of soft
tissues
b) Inactivation of enzymes: Enzymes bring about metabolic activities within the cells and this may
interfere with the characteristics of the tissue structures, fixatives are therefore used to inactivate
them. The importance of fixation is to make sure that there is no change that takes place after
removal or death of tissue hence the need to stop the action of enzymes. When the cells die the
lysosomes rapture thus releasing lytic enzymes that digest the surrounding tissue, inactivation of
enzymes is important to avoid such effects.
c) Anti- bacterial: Like the enzymes bacteria can cause distortion of the tissue structures resulting of
the rotting of tissue. Bacteria that may be present as commensals, from the environment or may
have brought about disease may continue multiplying bringing certain changes in the tissue. The
fixatives have the ability to kill such bacterial cells.
d) Increase of refractive index: Certain fixatives increase or raise the refractive indices. This will allow
the various tissue structures to be clearly seen during microscopic examination.
e) Introduction of pigments: Certain fixatives when used can impart unwanted pigments onto
tissues; this may mask the tissue structures to be examined microscopically. The pigment could
be oxides as a result of chemical reactions between the fixatives and chemical constituents of
tissue or due to the colour of the fixative used.
f) Health hazards: Some fixatives can bring about harmful effects to the user. Formaldehyde for
example when handled carelessly may cause sinusitis and dermatitis, while Osmic acid fumes may
result in blindness if in contact with eye tissue.
g) Swelling: Some fixatives may make the tissue swell that may be mistaken to be an abnormality
during examination of tissue.
h) Shrinkage: A large number of tissues may shrink the tissue to an extent that wrong diagnosis may
be given, the tissue may be very normal but due to its shrunken state it look abnormal.
i) Mordanting effect: Certain fixatives will give improved preservation and staining of some tissue
structures, such fixatives may be used as secondary or after initial fixation in another fixative.
No fixative can have all the qualities hence need to have knowledge on several fixatives for proper
preservation in different histological tissues
