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- 1Properties of a good fixative1. Penetrate tissue quickly & evenly
2. kills cells quickly & evenly = prevents edge effects
3. not cause excessive shrinkage, swelling or hardening - inc dessection & drying - can distort the original tissue state
4. have long shelf life & easy storage
5. safe to use, low toxicity & inflammability
6. should not produce artefacts - 2What is Tissue ProcessingEmbedding specimens in medium harder than the tissue to support the cells & hold the tissue in place to cut with sectioning blade
Via substituting aqueous fixative with non-water miscible paraffin wax - 3Stages of tissue processing - dehydrationmost fixative are aqueous,
dehydrating agent removes free & bound water molecules
most common agent - 99.85% ethanol, others: acetone, methanol
tissues processed through rising gradient of ethanol up to 99% - 4Stages of tissue processing - ClearingClearing agent is miscible with paraffin wax - 2-3 changes required
replaces the alcohol,
acts as a link between the miscible dehydrating agent & the paraffin
hydrocarbon eg. xylene, toluene, chloroform, petroleum solvents - 5Stages of tissue processing - Infiltrationparaffin wax replaces the clearing agent & infiltrates the tissue,
mixture of polycrystalline straight chain hydrocarbons,
melting point 39-68oC,
Higher MP = harder the wax
soft tissue - low MP wax
hard tissue - high MP wax,
usually between 56-58oC - 6Stages of tissue processing -EmbeddingInfiltrated tissue encapsulated by paraffin wax to provide rigid support for microtomy,
paraffin wax must be clean, filtered, & held at 2-4C above MP,
once completed - tissue basket is transferred to heated reservoir or a free standing bath of paraffin wax,
tissues removed by heated forceps placed face down in a preheated filled mould of molten wax - 75 categories of histological specimensA B C D E
- 8Category A of histological specimenSpecimens only requiring transfer from container to tissue cassette
- 9Category A of histological specimenSpecimens only requiring transfer from container to tissue cassette
- 10Category B of histological specimenSpecimens requiring transfer but with standard sampling, counting, weighing, or slicing
- 11Category C of histological specimenSimple dissection required with sampling needing a low level of diagnostic assessment and/or preparation
- 12Category D of histological specimenDissection and sampling required, needing a modest level of assessment
- 13Category E of histological specimenSpecimens requiring complex dissection and sampling methods
- 14Anionic DyesCombine with a tissue cation
- 15Cationic DyesCombine to a tissue anion,
Eg. Methylene Blue
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- Flashcards on Revision Flashcards, created by sam.wats on 29/07/2014.
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