02 Fixation Flashcards
first step in histotechnology
fixation
chemical process by which biological tissues are preserved from decay
fixation
process of preserving cells and tissue constituents in a life-like manner
fixation
basic mechanism in fixation
(additive / non-additive)
cross linking fixatives
additive
basic mechanism in fixation
(additive / non-additive)
chemical constituent taken into the cell, forming molecular complexes and stabilizing proteins
additive
basic mechanism in fixation
(additive / non-additive)
formalin, mercury, osmium tetroxide
additive
basic mechanism in fixation
(additive / non-additive)
fixing agent is not incorporated into the tissue
non-additive
basic mechanism in fixation
(additive / non-additive)
alteration of tissue composition by removing bound water molecule at hydrogen bonds within protein molecules
non-additive
basic mechanism in fixation
(additive / non-additive)
stabilizes proteins by forming crosslinks after water molecule removal
non-additive
satisfactory fixation occurs at what pH level?
6-8
high acidity ___ (increases/decreases) effectiveness
decreases
what is the relationship of temperature to the diffusion into the tissue?
direct (increased temp = increased diffusion)
what is the relationship of diffusion into the tissue and rate of chemical reaction between the fixative and tissue elements?
direct
temperature of fixation of surgical specimens
room temp
the fixation of surgical specimens can be followed by further fixation at what temperature after fixating it at room temperature?
40-45C
temperature of fixation:
electron microscopy
0-4C
temperature of fixation:
mast cells for EM
room temp
T/F: nucleic acids easily react with fixatives at room temp
F (do not react)
chemical reactions are rapid at ___ (low/high) temp
what temp?
high
60-65C
the thickness of the section to be fixed should be ___
1-2mm for EM
2cm for light microscopy
the brain is usually suspended whole in ___ buffered formalin for ___ weeks to ensure fixation and some hardening prior to secitoning
10%
2-3
hypertonic solutions give rise to ___ ___
cell shrinkage
isotonic and hypotonic fixatives cause ___ and ___ ___
swelling
poor fixation
the best results is usually obtained using slightly ___ (osmolality) solutions
what mOsm?
hypertonic
400-450
give the concentration of fixatives:
formaldehyde
10%
give the concentration of fixatives:
glutaraldehyde
3%
presence of buffer causes polymerization of ___, with consequent ___ (increase/decrease) in its effective concentration
aldehyde
decrease
give the concentration of fixatives:
glutaraldehyde for immunoelectrochemistry
0.25%
primary fixation in buffered formalin is usually carried out for ___ hours during the day the specimen is obtained
2-6
___ fixation may cause shrinkage and hardening of the tissue and may severely inhibit enzyme activity and immunological reaction
prolonged fixation
the specimen should be placed in a fixative solution as soon as it is removed from the body to prevent ___ and ___
autolysis and putrefaction
the volume of fixative should be ___ times the volume of the tissue to be fixed
10-25
the maximum effectiveness of fixation is noted to be ___ times the tissue volume
20
fibrous organ take ___ (longer/shorter) than small or loosely textured tissues such as biopsies or scrapings
longer
fixation time can be cut down using ___, ___, ___, or ___
heat
vacuum
agitation
microwave
to maintain an adequate fixation time of 4-6 hours, the tissue size must be ___ square
2cm
T/F: refrigeration is used to slow down decomposition if the tissue that needs to be photographed and cannot be fixed immediately
T
classification of fixative:
made up only of one substance
simple fixative
classification of fixative:
two or more fixatives to obtain optimal combined effect
compound
aldehyde fixatives used (2)
formaldehyde
glutaraldehyde
rmmbr: these are simple fixatives!
metallic fixatives used (3)
mercuric chloride
chromate fixatives
lead fixatives
(M-C-L)
rmmbr: these are simple fixatives!
classification of fixative:
preserve specific parts and particular microscopic elements
cytologic fixatives