Clearing Flashcards
Although dehydrated issue is now essentially water free it still cannot be infiltrated because _ are largely immiscible
Wax and ethanol
Is the process whereby alcohol or a dehydrating agent is removed from the tissue and replaced with a substance that will dissolve the wax in which issue is to be impregnated
clearing (de alcoholization)
Substance that will dissolve the wax with which the tissue is to be impregnated
Paraffin
Medium on which the tissue is to be mounted
Canada balsam
Aside from removing alcohol, a cleaning agent must also be miscible with
Canada balsam and other resins that are used for mounting sections
This stage in the process is called “clearing” because many (but not all) clearing agents impart an ___ or ___ to the tissue due to their relatively high refractive index
Optical clarity or transparency
Another important role of the clearing agent
remove a substantial amount of fat from the tissue
The most commonly used clearing agent for removing a substantial amount of fat from the tissue which otherwise presents a barrier to wax infiltration.
Xylene
used when the tissue is to be cleared directly from water, as in a frozen section.
Glycerin and gum syrup
A good clearing agent should be miscible with ___ to promote rapid removal of the dehydrating agent from the tissue.
Alcohol
A good clearing agent should be miscible with, and easily removed by ____ and/or by ____to facilitate impregnation and mounting of sections.
Melted paraffin wax, mounting medium
A good clearing agent should not produce excessive __, ___ or ___ of tissue
shrinkage, hardening or damage
A good clearing agent should not dissolve out
Aniline dyes
A good clearing agent should not _ in a water bath
Evaporate quickly
A good clearing agent should make tissues -
Transparent
Clearing fluids with a low boiling point are generally more readily replaced by
Melted paraffin
has a lower boiling point than xylene in fact takes longer than the latter to clear.
Chloroform
also affects the speed of penetration of the clearing agent.
Viscosity
Prolonged exposure to most clearing agents causes the tissue to become ___ and therefore more difficult to cut.
Brittle
a colorless clearing agent that is most commonly used in histology laboratories.
Xylene
Clearing time for xylene/xylol is usually
1/2-1 hour
xylene/xylol is generally suitable for most routine histologic processing schedules of ___ hours, and when the tissue block size is ___ mm.
<24hours, <5 mm
is reasonably cost effective and works well for short-term clearing of small tissue blocks.
Xylene
is one of the routinely used chemical in histology and pathology laboratories because of its vital role in the paraffin wax tissue processing method.
Xylene
xylene It is mostly used as ____ during tissue processing and as a ___ during staining
clearing agent, dewaxing agent
several toxicities believed to be caused by intermediate products of xylene metabolism such as ___ have been reported.
methyl benzaldehyde
Xylene is the most rapid clearing agent, suitable for urgent biopsies which it clears within
15 -30 minutes (advantage)
xylene is miscible with ___ and __.
absolute alcohol and paraffin. (advantage)
xylene does not extract out
aniline dyes. (advantage)
For mounting procedures, xylene does not dissolve ___ and can m therefore, be used for ___ sections.
celloidin, celloidin sections. (advantage)
it makes tissue transparent
xylene (advantage)
It evaporates quickly in ____ oven and can, therefore, be readily replaced by wax during impregnation and embedding.
paraffin oven (advantage), xylene
it is cheap
xylene (advantage)
it is highly inflammable and should be appropriately stored
xylene disadvantage
if used longer than ___ it makes tissues excessively hard and brittle
3 hours, xylene (disadvantage)
xylene causes considerable hardening and shrinkage of tissues; hence, is not suitable for ___ and ___
(disadvantage) nervous issues and lymph nodes
Xylene becomes milky when an _______ is immersed in it.
incompletely dehydrated tissue
may irritate eyes, nose and respiratory tract. It can be absorbed through the skin and cause dermatitis. At high concentrations, it is toxic and narcotic.
xylene disadvantage
Keep container tightly closed to prevent xylene from ___ and entering the ____.
subliming, entering the atmosphere.
Only _____ tools may be used to handle xylene.
non sparking
Store xylene in a
flammable liquid storage cabinet.
is better at preserving tissue structure and is more tolerant of small amounts of water left behind in the tissues than xylene.
toluene
more expensive than xylene and more toxic, so it is less commonly used.
toluene
may be used as a substitute for xylene or benzene for clearing both during embedding and mounting processes.
toluene
Time recommended for clearing for toluene
1-2 hours
it acts fairly rapidly and is recommended for routine purposes.
toluene (advantage)
Tissues do not become excessively hard and brittle even if left for 24 hours.
toluene (advantage)
clears overnight
toluene (advantage)
it is not carcinogenic
toluene advantage
toluene is slower than ___ and ___ (disadvantage)
xylene and benzene (disadvantage)
toulene tends to ___ in a partially filled vessel
acidify (disadvantage)
Highly concentrated solutions will emit fumes that are toxic upon prolonged exposure.
toulene (disadvantage)
it is more expensive
toluene (disadvantage)
preferred by some as clearing agent in the embedding process of tissues because it penetrates and clears tissues rapidly.
benzene
used to be a popular routine clearing agent until recently when its highly carcinogenic properties were recognized.
benzene
Its use for clearing purposes is therefore strongly discouraged.
benzene
It is rapid acting, hence is recommended for urgent biopsies (15-60 minutes) and routine purposes.
benzene (advantage)
volatilizes rapidly in paraffin oven and is therefore easily eliminated from the tissue.
benzene (advantage)
Benzene is miscible with
Absolute alcohol
causes minimum shrinkage
benzene (advantage)
benzene is highly _
Flammable
If a section is left in benzene for a long time, considerable ____ may be observed. Hence, tissues should be transferred to paraffin wax as soon as possible.
Tissue shrinkage
Excessive exposure to benzene may be extremely toxic to man and may become carcinogenic or it may damage the bone marrow resulting in ____
Aplastic anemia
If ever benzene is to be used for clearing, the laboratory should be _____.
Well ventilated
when used for clearing of tissues during the embedding process, is slower in action than xylene, but causes less brittleness.
Chloroform
Thicker tissue blocks, even those up to I cm. in thickness, can be processed.
chloroflorm
tissues placed in ___ do not become translucent.
chloroform
It is recommended for routine work
Chloroform
Chloroform is miscible with
absolute alcohol.
It is recommended for tough tissues (e.g. skin, fibroid and decalcified tissues) for nervous tissues, lymph nodes and embryos because it causes minimum shrinkage and hardening of tissues.
Chloroform
