List the disadvantages of using formalin as a fixative. - ️️1. rate of formalin fixation
is slow, complete fixation takes several days. (adequate in 8hrs)
2. may cause dermatitis in some workers
3. unbuffered formalin in solutions can produce precipitates in tissues (esp. blood-rich
tx)
4....
MEDL 310 - SIMPLE & COMPOUND
FIXATIVES
List the disadvantages of using formalin as a fixative. - ✔️✔️1. rate of formalin fixation
is slow, complete fixation takes several days. (adequate in 8hrs)
2. may cause dermatitis in some workers
3. unbuffered formalin in solutions can produce precipitates in tissues (esp. blood-rich
tx)
4. concentrated formaldehyde can polymerize, forming paraformaldehyde, reducing
working strength of solution and any formalin solution prepared from it.
What solution would remove the precipitate formed by fixation with mercuric chloride? -
✔️✔️alcoholic iodine
state the percent concentration of concentrated formaldehyde. - ✔️✔️40% w/v
State the working strength of formalin solutions. - ✔️✔️10% w/v
Is formalin a coagulating or non-coagulating fixative? - ✔️✔️noncoagulating
State the pH ranges at which formalin can be used. - ✔️✔️7 - 7.5 or 8-9
List the advantages of using formalin as a fixative. - ✔️✔️1. penetration rate is fast, but
fixation rate is slow due to the time needed to form cross-linkages.
2. allows less shrinkage of tissues in subsequent processing steps
3. results in hardening of tissue, but doesnt overharden
4. inexpensive
5. solutions are relatively stable, especially if buffered.
6. Many staining methods can be performed after fixation
7. tissues may be processed in many different ways after fixation, even frozen sections.
When will formalin precipitate form? - ✔️✔️if the solution of formalin becomes acidic
What solutions will remove a formalin precipitate? - ✔️✔️alcoholic picric acid or 2%
ammonia in 80% alcohol
What is the molecular formula for formalin? - ✔️✔️H2CO
What is the fixative volume to tissue volume for formalin and most other fixatives? -
✔️✔️Fixative volume should be 15-20 times the volume of the tissue.
, Is mercuric chloride a coagulating or non-coagulating fixative? - ✔️✔️coagulating
Name the precipitate formed when using mercuric chloride-containing fixatives. -
✔️✔️mercury precipitate
What is the molecular formula for mercuric chloride? - ✔️✔️HgCl2
What is the molecular formula for potassium dichromate? - ✔️✔️K2Cr2O7
In what fixative solutions is potassium dichromate used? - ✔️✔️compound fixatives -
eg Zenker's, Hellys
Is acetic acid a precipitating or non-precipitating fixative? - ✔️✔️precipitating
List the advantages of using acetic acid. - ✔️✔️precipitation of nucleoproteins, tissue
swelling to counteract shrinkage of other fixing agents in compound fixatives.
List the disadvantages of using acetic acid. - ✔️✔️- destroys Golgi apparatus and
mitochondria
- Can cause considerable tissue swelling if used alone
Is picric acid a coagulating or noncoagulating fixative? - ✔️✔️coagulating
List the pros and cons of using picric acid. - ✔️✔️Pros: enhances tissue staining, and
the yellow coloration provided makes small biopsies easy to find or ID. Enhances
glycogen preservation. Yellow color easily removed during dehydration.
Cons: causes or allows considerable shrinkage to the tissues, cannot wash in water or
the protein picrates formed will be solubilized.
What is the molecular formula for picric acid? - ✔️✔️C6H2(NO2)3OH
Is ethanol a precipitating or nonprecipitating fixative? - ✔️✔️precipitating
What is the molecular formula for ethanol? - ✔️✔️CH3CH2OH
State the common uses for ethanol as a fixing reagent. - ✔️✔️used to precipitate
glycogen, and for enzyme demonstration
How may aldehyde groups does glutaraldehyde have? - ✔️✔️two
Is glutaraldehyde a coagulating or noncoagulating fixative? - ✔️✔️noncoagulating
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