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MODULE
Tissue Processing
Histology and Cytology
7
TISSUE PROCESSING
Notes
7
...
This describes the steps required to take animal and human tissues from fixation
to the state where it is completely infiltrated with a suitable wax i
...
paraffin wax
and can be embedded and ready for section cutting on microtome
...
Aim: To process the fixed tissue into a form in which it can be made into thin
microscopic sections
...
Dehydration: It is the process of removing water from tissues
...
Dehydration is usually complete
when less then 3-4% of water remains in the tissues
...
Permeability of tissues
2
...
Temperature
4
...
The most commonly used dehydrant is ethyl alcohol
...
Concentration of first alcohol bath depends on the
fixative and size and type of the tissue, e
...
delicate tissue needs lower
concentration of alcohol and smaller interval between two strengths of alcohol
...
After about 40 tissues have passed through the first change of alcohol,
it is discarded and all the other changes are brought one step lower
...
Usually tissues are kept in each solution for 40 to 60 minutes
...
Anhydrous CuSO4
removes water from alcohol as it in turn removes it from tissues
...
Therefore,
it acts as an indicator for the presence of water
...
Rapid dehydration
2
...
Blue colouration of CuSO4 indicates that both alcohol and CuSO4 should
be changed
...
It is used for complete dehydration
...
Advantages
z
Rapid action
z
Easily removed by most clearing agents
z
Less expensive
Disadvantages
z
Highly volatile
z
Causes shrinkage and brittleness of tissues
z
Dissolves lipid more than ethanol
Clearing – Clearing is a process which leaves the tissues clear and transparent
...
If the refractive index of the clearing agent is similar to the protein
of tissue the tissue becomes transparent
...
Thus clearing serves two purposes
MODULE
Histology and Cytology
1
...
Acts as solvent for the mounting media which renders the tissues transparent
and improves the refractive index, making microscopic examination easier
...
Two changes of one hour
each are given to get the end point
...
It is not preferred for brain tissue