Histopathologic Techniques Quiz

Study Notes

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.

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.

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.

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.

Chromic Acid: Effective in preserving carbohydrates.
Potassium Dichromate: Preserves mitochondria.
Regaud’s (Muller’s) Fluid: Demonstrates various cellular structures; used for 12-48 hours.

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.

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.