PRELIM: CH6 Fixation

Preserve morphologic and chemical integrity by halting autolysis and putrefaction

The primary purpose of fixation in histotechnology is to:

Autolysis due to lysosomal enzyme activity

Failure of timely fixation primarily leads to:

Fixative forms cross-links and becomes part of the tissue

Which statement best describes additive fixation?

Removing bound water and promoting new protein cross-links

Non-additive fixation stabilizes tissue mainly by:

It conveniently exposes all tissue surfaces to fixative

In routine practice, immersion fixation is commonly used because:

20:1 fixative:tissue ratio

Which is a correct practical rule for fixative volume?

Insufficient fixative volume relative to tissue

The most frequent histotechnology error in fixation is:

6–8 (near neutral)

Optimal pH for fixation to minimize ultrastructural damage is:

Formalin-heme pigment (acid formalin pigment)

Acidic formalin increases risk of which artifact?

Phosphate

A buffer commonly used to stabilize formalin pH is:

Increase fixation rate but may increase autolysis if excessive

Increasing temperature during fixation will:

0–4°C

For EM (electron microscopy), primary fixation is typically performed at:

≤4 mm

Typical tissue block thickness for good formalin penetration in LM (light microscopy) is:

2–3 mm/hour

A quoted rate for aldehyde fixative penetration is approximately:

Under-fixation of the interior with autolysis

Inadequate trimming of a large uterus before fixation primarily risks:

Slightly hypertonic solutions (400–450 mOsm)

Regarding osmolality, best results are often obtained using:

Formaldehyde 10%, glutaraldehyde 3%

Which fixative concentration pairing is standard?

Shrinkage and swelling artifacts

Over-fixation most likely causes:

Brittleness and hard blocks

Prolonged fixation commonly results in:

Delays promote autolysis and putrefaction

Time from tissue removal to fixation is critical because:

Stable, safe, rapid, and minimally distorting

A good fixative should ideally be:

Cross-linking proteins

Aldehyde fixatives act primarily by:

Oxidizing cross-linkers

Osmium tetroxide and potassium permanganate are:

Denature and precipitate proteins

Alcohol-based fixatives (e.g., ethanol, methanol) primarily:

Forming insoluble metallic precipitates (e.g., mercuric chloride)

Metallic fixatives act by:

10% neutral buffered formalin

A microanatomical fixative suitable for general tissue architecture is:

Glacial acetic acid

Nuclear fixatives typically contain:

Glacial acetic acid

Cytoplasmic fixatives must avoid:

Precipitant fixatives: ethanol or acetone

For preserving RNA quantitatively, the preferred fixatives are:

Improve demonstration of substances and act as a mordant for special stains

Secondary fixation is used to:

Potassium dichromate 2.5–3%

Post-chromatization commonly uses:

50–70% alcohol

Washing out picric acid (e.g., from Bouin’s) is best done with:

Alcoholic iodine

Removing excess mercuric fixative residues is best accomplished with:

Treat as potentially infectious

A critical handling precaution for fresh tissue is to:

Ice crystal artifacts form

Slow freezing of unfixed tissues near 0°C should be avoided because: