Modules 11-17 Flashcards
9 steps that occur in the histopathological technique
Gross cutting Fixation Dehydration Clearing Infiltration Embedding Sectioning Staining Microscopic examination
4 main categories for instrument QC in the histopathology lab
Lubrication
Temperature
Cleaning
Maintenance
Biopsy
The removal of a small piece of living tissue from an organ or other part of the body for microscopic examination to confirm or establish a diagnosis, estimate prognosis, or follow the course of a disease
Curettage
Scraping of material from a cavity wall or other surface to obtain tissue for microscopic examination or remove tumor or other abnormal tissue
6 major sections of the pathway of a surgical specimen
Accessioning, processing, pathologist (gross + slides), additional requirements, reports, filing
Maximum size of tissue that can be processed in a cassette
2 x 3 x 0.3 cm
Fixative
A substance that alters tissue through the stabilization of protein, so that it is resistant to changes in subsequent treatments of the tissue
Preservative
A preservative will not swell, shrink or distort tissues, but it does not alter the tissue structure and therefore will not protect it from changes in subsequent treatments of the tissue
Autolysis
The breakdown of tissues by enzymes in the tissues that continue their metabolic actions once tissues are removed from the body
Putrefaction
The breakdown of tissues by bacterial action
7 functions of a fixative
Prevent autolysis Prevent putrefaction Stabilize tissue structure Lessen shrinkage and distortion of tissue on subsequent processing Change the refractive index of tissue Enhance staining Make tissue firmer
Additive fixative
Adds on to or chemically links to the tissue, changing the tissue by its addition
Nonadditive fixative
React with the tissue, but do not add onto or combine with the tissue in order to act on it
Coagulant fixative
Produce aggregation of protein molecules, granulation and precipitation
Result is the production of a meshwork through which other solutions can easily penetrate
Non-coagulant fixative
Form addition compounds with proteins
6 factors that affect fixation
Time, temperature, size, volume of fixative to tissue volume, pH, storage osmolality
What temperature can be used to speed fixation without significantly affecting the tissue?
45C
The optimal thickness for a tissue to be routinely processed
Less than 3mm
The optimal amount of fixative to be used in relation to the volume of tissue
15-20x the volume of the tissue
2 ways to transport unfixed tissue
Place biopsy on a piece of gauze dampened with saline, in a sealed container transported on ice. Or, place in container of Michel transport solution
2 storage fluids that may be used
Neutral buffered formalin or 70% alcohol
When should tissue be transferred to 70% ethanol?
When fixative other than formalin was used or if immunohistochemical studies are likely
When is no fixation of a specimen required?
Immunofluorescence, enzymes, some immunohistochemistry studies, and most methods using frozen sections
Postfixation
When a tissue which is already fixed, is fixed again, using another fixing agent that would enhance its staining properties
2 reagents that may be used to “postfix” a tissue
Bouin’s or osmium tetroxide
Is formalin a coagulating or noncoagulating fixative?
Noncoagulating
The pH ranges at which formalin may be used
pH 7-7.5 or pH 8-9
Advantages of using formalin as a fixative
Penetration rate is fast
Less shrinkage of tissue
Hardening of tissue
Inexpensive
Solutions are stable
Many routine, special, and histochemical staining methods may be performed after formalin fixation
After fixation, tissues may be processed in paraffin, celloidin, plastics, or used for frozen sections
Disadvantages of using formalin as a fixative
Rate of fixation is slow
May cause dermatitis
Unbuffered formalin in solutions can produce precipitates in tissue
Concentrated formaldehyde can polymerize forming paraformaldehyde, reducing the working strength of the formaldehyde solution
When will formalin precipitate form?
If the formalin solution becomes acidic
Solution used to remove formalin precipitate
Alcoholic picric acid or 2% ammonia in 80% alcohol
Is mercuric chloride a coagulating or noncoagulating fixative?
Coagulating
Which fixative causes a diffuse PAS reaction in tissues?
Glutaraldehyde
What is the best dehydrant?
Ethanol
What is the best substitute for ethanol as a dehydrant?
Isopropanol
Universal solvent
A solution that performs both dehydration and clearing steps of processing. eg. dioxane, tertiary butanol and tetrahydrofuran
Result of leaving tissue in dehydrating alcohols or clearing agents for extended periods of time
Tissue will be hard, shrunken, and difficult to section. Nothing can be done to fix this issue.
Infiltration
The use of a support media that will permeate all the tissue spaces and maintain the structural integrity of the tissue
Most commonly used infiltrant
Paraffin wax
Disadvantages of using a rotary tissue processor
Slow, fumes, carryover
The most common type of microtome in use in histopathology labs
Rotary microtome
Freeze-drying
Instantaneous freezing of tissues which stops all vital processed
3 steps in the freeze-drying technique
Quenching, drying, sectioning
