PAGE 1 Flashcards
first and most critical step in tissue processing
FIXATION
fixing or preserving fresh tissue for examination
FIXATION
should be done immediately to preserve cellular and tissue morphology
FIXATION
2 PURPOSES OF FIXATION
- PRESERVATION
2. PROTECTION
PRIMARY PURPOSE OF FIXATION
PRESERVATION
SECONDARY PURPOSE OF FIXATION
PROTECTION
capable of forming cross-links between proteins
FIXATIVE AGENTS
stabilizes tissue components making them insoluble to lysosomal enzymes
CROSS-LINKS
TYPES OF FIXATIVE
- ADDITIVE
2. NON-ADDITIVE
becomes part of the cross-link itself
ADDITIVE
facilitates the removal of water in order for cross-links to form
NON-ADDITIVE
capable of inactivating lysosomes
DEHYDRANT FIXATIVE
FIXATION IS RETARDED BY
- Increase in size and thickness
- Presence of mucus
- Presence of fats
- Presence of blood
- Decrease in temperature
FIXATION IS ENHANCED BY
✓ Decrease in size and thickness
✓ Presence of agitation
✓ Presence of heat
FACTORS TO BE CONSIDERED IN FIXATION
- pH
- TEMPERATURE
- SIZE AND THICKNESS
- OSMOLALITY
- CONCENTRATION
- VOLUME
pH FOR FIXATION
6 TO 8
TEMPERATURE FOR ROUTINE MANUAL
ROOM TEMPERATURE (20 to 22oC)
TEMPERATURE FOR ROUTINE AUTOMATED
40 oC
TEMPERATURE FOR ELECTRON MICROSCOPY
0 to 4oC
TEMPERATURE OF FORMALIN FOR VERY URGENT BIOSPSIES
60 oC
TEMPERATURE OF FORMALIN FOR DIAGNOSIS OF TUBERCULOSIS
100 oC
TEMPERATURE FOR DNA
65 oC
TEMPERATURE OF RNA
45 oC
SIZE AND THICKNESS FOR LIGHT MICROSCOPY
2cm2 by 0.4cm thick
