Questions and Answers
What is the best general tissue fixative?
What is the working solution concentration of Neutral Buffered Formalin?
10%
Formaldehyde is a good fixative for immunohistochemical staining.
False
What particular structures does Glutaraldehyde preserve?
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Which fixative is recommended for urgent biopsy specimens?
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Methyl Alcohol is primarily used for fixing __________ and blood smears.
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Match the following fixatives with their uses:
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Ethyl Alcohol can be mixed with chromic acid and potassium dichromate.
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What are Carnoy's Fixative advantages?
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Which fixative is known for preserving carbohydrates?
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Gendre’s solution is an improvement upon ___________ solution.
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Which fixative is ideal for fixing chromosomes?
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What can happen if you use too high a concentration of formaldehyde?
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Study Notes
Aldehyde Fixatives
- Formaldehyde (Formalin): Pure stock at 40%, working solution generally at 10%; best for tissue preservation, prevents autolysis, and maintains morphology.
- Neutral Buffered Formalin (10%): Common choice for general tissue fixation; advantages include cost-effectiveness, tissue penetration, and compatibility with stains; disadvantages include mucosa irritation and potential staining issues.
- 10% Formal-Saline: Combination of formaldehyde and sodium chloride; ideal for CNS and general tissues; preserves microanatomical structures with minimal distortion.
- Glutaraldehyde (2%; Cold and buffered): Slower diffusion than formaldehyde; excellent for cytoplasmic/nuclear detail, stable in CNS tissues; not suitable for immunohistochemistry due to protein alteration.
- Karnovsky’s Fixative: Contains paraformaldehyde and glutaraldehyde; used for electron and light microscopy with resin embedding.
Alcoholic Fixatives
- Methyl Alcohol (100%): Fixes bone marrow and blood smears; dehydrates and fixes simultaneously.
- Isopropyl Alcohol (95%): Used for touch preparations.
- Ethyl Alcohol (70-100%): Simple fixative; used in histochemistry but can lyse RBCs at low concentrations and cause glycogen polarization.
- Carnoy’s Fixative: Rapid fixation (1-3 hours); preserves glycogen and Nissl granules; not suitable for large tissues due to excessive hardening.
- Clarke’s Solution: For frozen sections and smears; acts efficiently within 3-4 hours.
Metallic Fixatives
- Mercuric Chloride: A secondary fixative that penetrates slowly and hardens tissue, often requiring decolorization.
- Zenker’s Solution: Recommended for trichrome staining; excellent for congested tissues but not suitable for frozen sections.
- Lillie’s B-5 Fixative: Combines formaldehyde and mercuric chloride; rapid structural stabilization, used for bone marrow biopsies.
Oxidizing Agents
- Osmium Tetroxide: Used for EM; fixes fats and maintains cytoplasmic structures, but expensive and irritating.
- Flemming's Solutions: Common for nuclear structures; one variant excludes acetic acid for cytoplasmic fixation.
Chromate Fixatives
- Chromic Acid: Effective in preserving carbohydrates.
- Potassium Dichromate: Preserves mitochondria.
- Regaud’s (Muller’s) Fluid: Demonstrates various cellular structures; used for 12-48 hours.
Picric Acid Fixatives
- Bouin’s Solution: Good for embryos and pituitary biopsies; can cause RBC hemolysis but excellent for glycogen demonstration.
- Hollande’s Solution: Suitable for gastro-intestinal and endocrine tissues; has decalcifying properties.
Other Fixatives
- Glacial Acetic Acid: Preserves DNA by precipitating nuclei; important for chromosomal studies.
- Michel’s Solution: A transport medium, not a fixative; unsuitable for certain cytometry applications or immunofluorescence.
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Description
Test your knowledge on histopathologic techniques with a focus on aldehyde fixatives such as formaldehyde. This quiz examines the properties and applications of various fixatives in histology. Perfect for students and professionals in the field of pathology.
