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Related Flashcards
Cards In This Set
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What is the purpose of dehyration? What happens if a specimen is left too long in the dehydrating agent?
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To remove only the FREE water; if left too long, bound water gets removed as well and the tissue gets too hard.
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What are some examples of dehydrating agents?
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Ethanol, methanol, isopropanol, acetone, universal agents
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What are some examples of clearing agents?
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Xylene, Benzene, Chloroform, natural agents (essential oils, limonene)
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What is the approximate melting point of paraffin? What is the temp of the melting bath?
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56 - 58 degrees; few degrees higher (SMH used 60)
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What are some examples of decalcifying agents?
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Nitric acid, formic acid, HCl, EDTA
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When would you use an aqueous mounting medium?
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Used for fat stains (Oil Red O); impermanent; doesn't harden
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List some changes that occur when tissues are not fixed fast enough?
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Eosinophilia, cellular swelling, glycogen disappears, microvilli & cilia lost, desquamation, nuclear changes/disintegration, autolysis, putrefaction
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What is the difference between an additive fixative & a non-additive fixative? Give examples of each.
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Additive: the fixative binds to the protein rendering it insoluble; (FDOG: formalin, dichromates, osmium tetroxide, glutaraldehyde)
Non-additive: the fixative does not bind to the protein! (acetone and alcohols) |
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What is the difference between a coagulant fixative & a non-coagulant fixative? Give examples of each.
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A coagulant fixes the tissue into an OPEN network which allows for easy penetration/subsequent processing; Examples: alcohol, picric acid, chromium, mercuric chloride
A non-coagulant fixes the tissue into a dense gel; Examples FDOG: formalin, dichromates, osmium tetroxide, glutaraldehyde |
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What % of formaldehyde is present in 100% formalin? What % formalin is used as a "working solution" in the lab?
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37% formaldehyde in 100% formalin.
We use a 1:10 (10%) working solution; this would contain 3.7% formaldehyde. |
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How can paraformaldehyde precipitate formation be removed/reversed? How can it be prevented?
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Reverse with heat, or prevent by adding methanol.
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How can formalin pigment be removed? What types of tissues would it be seen in?
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Remove by adding alcoholic picric acid
Seen in bloody tissues. |
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What are the 2 steps of formaldehyde fixation? (organic chem!)
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Hemiacetal formation & methylene bridge formation
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Which fixatives make lipids insoluble?
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Potassium dichromate and osmium tetroxide
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Why is acetic acid added to some fixatives?
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It precipitates nucleic acids to improve nuclear detail
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