fixation Flashcards
First and most critical step in HTP
fixation
process that preserves tissues from decay, thereby preventing autolysis or putrefaction
fixation
improves ____ makes cell ___ to the effects of chemicals used in processing and improves ___ ___
staining, resistant, microscopic examination
fixatives employed prevent autolysis by inactivating ___ enzymes
lysosomal
fixatives have ___ effect that protect tissue from pathogen
bactericidal
Primary goal of fixation
preserve the morphologic and chemical integrity of the cells
second goal
to harden and protect tissue from the trauma so that it is easier to cut and process for microscopy
Fixation can be done using chemical solutions known as ___
fixatives
physical methods include:
eating, microwaving, cryo-preservation, freezants such as liquified CO2 or liquified nitrogen or freon gas
CO2 fixes at what temperature?
-7C
Liquid nitrogen
-180C
freon
-20C
Specimens should be transferred to fixative quickly <__ hour after surgery?
1
volume of solution : specimen
20:1 or 10:1
prolonged fixation may result in loss of ____ ____
immunohistochemical antigenicity
main factors involved in fixation
volume
20:1 - fixative volume to tissue
main factors involved in fixation
hydrogen ion concentration
best if in 6-8 level
common buffer
phosphate or bicarbonate
factor in fixation
thickness of section
- EM = __ - __mm
- LM = __mm
- 1-2 mm for
- 2mm
factor in fixation
osmolality
recommended solution
isotonic solution
factors in fixation
temperature
- tissue processors ____C
- electron microscopy ____C used for ____
- Refrigeration ___C
- 40C
- 0C - 4C, histochemistry
factors in fixation
concentration
As ___ as possible concentration of solution
formalin ideal concentration ___
glutaraldehyde concentration ___
lowest
10%
3%
factors in fixation
duration of fixation
formalin fixation duration - __ hours
formalin is washed out after __ hours
2-6 hours
24 hours
factors in fixation
time interval
.
characteristics of a good fixative
cheap
stable
safe to handle
kills the cell quickly to minimize distortion of cell constituents
characteristics of a good fixative pt.2
inhibits bacterial decomposition and autolysis
minimum shrinkage of tissues
permits rapid and even penetration of tissues
hardens tissue for easier cutting
isotonic
makes cellular components soluble to hypotonic solutions
permits subsequent application for staining procedures
washing out agents
tap water - used to remove excess ___, ___, and ___
chromates, formalin, and osmic acid
washing out agents
50-70% alcohol washes out ___
picric acid (Bouin’s solution)
washing out agents
alcoholic iodine removes excess ___
mercuric fixatives
failure to arrest early autolysis of cell
insufficient fixative
removal of substances soluble in fixing agent
wrong choice of fixative
presence of artifact pigments on tissue section
incomplete washing of fixative
tissues are soft and feather-like in consistency
incomplete fixation
loss or inactivation of enzymes
wrong choice of fixative
shrinkage and swelling of cells and tissue structure
overfixation
tissue blocks are brittle and hard
prolonged fixation
fixation artifact
well-known artifact that is produced under acid condition
formalin pigment
artifact
may be found in surgical specimens particularly in liver. associated with intense eosinophilic staining at the center
crush artifact
