HTL 4312 Histotechnology Review: Fixation, Processing, Microtomy, Staining, and Microscopy

Comprehensive practice flashcards covering fixation mechanisms, troubleshooting tissue processing, microtome angles, H&E staining formulations, and microscopy principles from HTL 4312.

What macroscopic and microscopic issues indicate incomplete or improper fixation?

Tissue appears raw/pink macroscopically, exhibits distorted cell morphology due to autolysis, appears under-stained or difficult to stain, and develops nuclear bubbling.

What indicates reagent contamination during clearing, and what corrective action must be taken?

If xylene appears contaminated or milky, it indicates the alcohols contain water; reagents must be rotated, the absolute alcohol replaced, and xylene replaced.

What visual criteria define a properly stained routine H&E slide?

Nuclei are blue/purple (stained by hematoxylin), cytoplasm displays three distinct shades of pink (stained by eosin), and nuclei are clearly distinguishable from cytoplasm.

What are the primary purposes of tissue fixation?

Fixation prevents autolysis and putrefaction, preserves tissue morphology in a life-like condition, stabilizes proteins, and renders tissue components insoluble.

What are the ideal characteristics of a histological fixative?

It brings out differences in the refractive indexes of tissue components without altering the refractive index, does not shrink or swell tissue, does not distort tissue components, and inactivates or kills bacteria.

How do coagulant and non-coagulant fixatives differ in their mechanism and reaction speed?

Coagulants denature proteins to form a sponge-like mesh network and are fast acting, whereas non-coagulants act slowly and stabilize tissue by forming crosslinks.

What defines additive fixatives versus non-additive fixatives?

Additive fixatives chemically link to or add themselves to tissue components, whereas non-additive fixatives act by displacing water within the tissue.

According to the fixative classification flowchart, which chemical agents are classified as additive coagulants?

Mercuric chloride, chromic acid, picric acid, and zinc salt.

Which fixatives are classified as additive non-coagulants?

Formaldehyde, glutaraldehyde, glyoxal, osmium tetroxide, potassium dichromate, and acetic acid (for cytoplasm).

Which fixatives are classified as non-additive coagulants?

Alcohols, acetone, and acetic acid (for nuclei).

What causes formalin pigment, how is it prevented, and how can it be removed from sections?

Cause: Formalin-containing fixatives in an acidic environment with $\text{pH} < 6.0$. Prevention: Using a buffered solution. Removal: Treating sections with saturated picric acid/alcohol.

What causes mercury pigment, how can it be prevented, and how is it removed prior to staining?

Cause: Mercury-containing fixatives. Prevention: Cannot be prevented. Removal: Treating tissue sections before staining with iodine, sodium thiosulfate, and a water rinse.

What causes chromate salts and how are they managed in tissue sections?

Cause: Dichromate fixatives. Prevention/Removal: Washing tissue thoroughly in running water (cannot be completely removed). Treatment: Treating with $1\%\,\text{HCl}$ in $70\%\,\text{alcohol}$ to reduce pigment levels.

What reagents are utilized for tissue dehydration and what is the primary purpose of this step?

Reagents include alcohols (ETOH, methanol, isopropanol, butanol, or acetone) to remove water from tissue and prepare it for the clearing stage.

What reagents serve as clearing agents and why must dehydration precede xylene clearing?

Reagents include xylene (routine), benzene, toluene, chloroform, or limonene derivatives. Dehydration must precede clearing because xylene is miscible with ETOH but immiscible with water.

What is the function of paraffin during the infiltration/impregnation step?

Paraffin penetrates tissue to provide internal rigidity and structural support, preparing the block for embedding and microtomy.

What are three universal solvents used in tissue processing, and why are they rarely employed routinely?

Dioxane, tertiary butanol, and tetrahydrofuran; they dehydrate and clear simultaneously but are rarely used because their slow diffusion rate can distort tissue morphology.

How does under-dehydration differ from over-dehydration in gross tissue appearance?

Under-dehydrated tissue is mushy, whereas over-dehydrated tissue is dry, friable, and prone to breaking.

What angle is designated between the paraffin block face and the lower bevel of the microtome blade in this diagram?

The clearance angle, which routinely measures between $3^\circ$ and $8^\circ$.

In the microtome knife profile diagram, which angle extends past the cutting facet?

The wedge angle, which routinely measures between $15^\circ$ and $18^\circ$.

What is the defined degree measurement for the bevel angle of a microtome blade?

$27^\circ\text{ to }32^\circ$ (the rake angle has no specified degree measurement).

What microtomy defects are caused by a dull blade versus a blade with physical defects?

A dull blade prevents ribbon formation, lifts sections off the block upon return strokes, and causes chatter; blade edge defects cause linear scrapes and scratches across the tissue.

What are the chemical properties, charge, and target affinity of hematoxylin?

Hematoxylin is basic (cationic/positively charged) and acidophilic; it stains anionic cellular components such as the nucleus blue/purple once oxidized to hematein.

What are the chemical properties, optimal pH range, and staining target of eosin?

Eosin is acidic (anionic/negatively charged) and basophilic; it stains positively charged cytoplasmic structures at an optimal $\text{pH}$ of $4.6\text{ to }5$, requiring no mordant.

Which anatomical components correspond to the three shades of pink produced by eosin?

Dark pink corresponds to red blood cells; middle/bubblegum pink corresponds to muscle and epithelial cells; light/baby pink corresponds to collagen.

How do stains and dyes differ by definition, and which histological reagents exemplify each?

A stain acts at the surface-level and requires a mordant (e.g., hematoxylin), whereas a dye is absorbed directly by tissue without requiring a mordant (e.g., eosin).

What is the operational distinction between a decolorizer and a differentiator?

A decolorizer removes color or excess color, whereas a differentiator specifically removes excess stain.

What is the chemical function of blueing, and why is tap water preferred over deionized water?

Blueing shifts hematoxylin from reddish to crisp blue/purple; tap water is preferred over DI water because inherent mineral impurities facilitate the blueing reaction.

What are the constituents, type, and characteristics of Harris hematoxylin?

Constituents: absolute ETOH (preservative), ammonium aluminum sulfate (mordant), distilled water (stabilizer), and sodium iodate (oxidizer). Type: progressive and regressive. Characteristics: most routine formulation with excellent nuclear staining.

What unique ingredients are present in Mayer's hematoxylin and what staining method does it use?

Mayer's hematoxylin contains citric acid and chloral hydrate (for $\text{pH}$ control), distilled water (solvent), sodium iodate (oxidizer), and ammonium or potassium aluminum sulfate (mordant); it is used progressively.

What distinguishing stabilizer is used in Gill's hematoxylin formulation?

Ethylene glycol (along with distilled water, sodium iodate, aluminum sulfate mordant, and glacial acetic acid).

Why are Erlich and Delafield hematoxylins not recommended for routine histopathology?

Both formulations require an extended natural oxidation period of $3\text{ to }6\text{ months}$; Delafield contains $\text{HCl}$ with no chemical oxidizer, while Erlich contains $95\%\,\text{ETOH}$ and glacial acetic acid.

What distinguishes iron hematoxylins from alum hematoxylins, and what is the key ingredient in Verhoeff's hematoxylin?

Iron hematoxylins (such as Weigert and Verhoeff's) resist acid extraction, unlike alum hematoxylins; Verhoeff's distinguishing mordant ingredient is Lugol's iodine.

What is a histological 'lake', and what reagent serves as a blue substitute for hematoxylin?

A lake is a complex formed by a mordant and a dye ($\text{Mordant} + \text{Dye} = \text{Lake}$); Celestine blue serves as an alternative to hematoxylin.

What are the 13 sequential steps in routine H&E staining?

1. Heat slides, 2. Deparaffinize with xylene, 3. Hydrate with decreasing alcohols, 4. Hematoxylin, 5. Rinse, 6. Differentiate (if regressive), 7. Blueing, 8. Rinse, 9. 95% ethanol, 10. Eosin, 11. Differentiate and dehydrate with increasing alcohols (if progressive), 12. Clear with xylene, 13. Coverslip.

What are the standard objective lens magnifications found on a routine light microscope?

$4\times$, $10\times$, $40\times$, $60\times$, and $100\times$ (used dry or with immersion oil).

How do the aperture/condenser and iris diaphragm regulate illumination in a compound light microscope?

The aperture/condenser concentrates and focuses light upward through the specimen into the objectives, whereas the diaphragm/iris modulates the intensity and diameter of the projected cone of light.

What specific histology specimens or targets are visualized using polarizing, phase-contrast, dark-field, and fluorescence microscopes?

Polarizing: birefringent materials, crystals, and urates; Phase-contrast: unstained tissue and refractive index shifts; Dark-field: unstained microorganisms and autoradiographic silver grains; Fluorescence: autofluorescent collagen, IHC fluorophores, and bacteria under UV light.