Fixation (Part 1) Flashcards
Step in tissue processing that involves preservation
FIXATION
Primary goal of fixation
To preserve tissues as close to the original as possible
Secondary goal of fixation
- Harden the tissue to facilitate easy cutting (into thin slices)
- Protect the tissue from trauma of further handling that might be caused by different reagents used in tissue processing
If processing lung specimen (which is thicker than other specimen), the required size is
1-2 cm
pH of fixatives
should be 6-8
The osmolality of fixative should be
Slightly hypertonic but practically, we use isotonic
Hypotonic fixative will cause
swelling
Hypetonic fixative will cause
Shrinking
Why do we not use concentrated solutions?
It will damage the tissue
Maximum effectiveness of fixative
20x the volume of the specimen
Ratio of fixative to tissue
15-20:1
When do preservation of tissue happens?
When the fixative penetrates the tissue
Penetration rate of formalin
1mm per hour
few fixatives used for Electron Microscopy; used 5-10x the volume of the specimen
Osmium tetroxide
Time and Duration of fixation
Should be 24-48 hours
Temperature for manual fixation
Room temp
Temp for Electro Microscopy and Histochemistry
0-4degC
Temp for autotechnicon
40degC *heat is applied to speed up the process
Factors to be considered when using the RIGHT fixative
- Urgency of the case
- Type of tissue to be processes
- Tissue structure to be studied
- Staining technique to be applied
- Type of section to be made
If urgent biopsy, this is used because it is a fast-acting fixative
Formalin
can be used to preserve brain tissues for the diagnosis of rabies
Carnoy’s solution and acetone
Cannot be used for kidney specimens
Bouin′s solution
The routine stain used in Histopath since it is compatible with many fixatives
H&E
An example of a fixative that can inhibit hematoxylin.
Osmium Tetroxide
