Histological Preparation and Observing Samples – Vocabulary

Vocabulary flashcards covering essential terms, fixatives, processing steps, stains, and common artefacts involved in histological preparation and sample observation.

Histological Preparation

Series of laboratory steps (fixation, embedding, sectioning, staining, mounting) used to create microscope slides from biological tissue.

Fixation

Chemical preservation of tissue that halts autolysis and putrefaction while maintaining structural integrity.

Embedding

Infiltrating fixed tissue with a supportive medium (usually paraffin wax) that hardens to permit thin sectioning.

Sectioning (Microtomy)

Cutting embedded tissue into very thin slices (3–10 µm) with a microtome for microscopic examination.

Staining

Applying dyes to sections so specific cellular or extracellular components become visible under light microscopy.

Mounting

Permanently attaching a stained section to a slide with a coverslip and mounting medium for preservation and viewing.

Autolysis

Self-digestion of tissue caused by endogenous enzymes when fixation is delayed or inadequate.

Putrefaction

Tissue decay produced by bacterial or fungal action; prevented by prompt fixation.

10 % Neutral Buffered Formalin (NBF)

Standard fixative containing 4 % formaldehyde buffered to neutral pH; gold standard in histopathology.

Glutaraldehyde

Dialdehyde fixative providing rapid, ultrastructural preservation; commonly used for electron microscopy.

Alcohol Fixatives

Methanol or ethanol solutions that fix by dehydration and protein precipitation; used widely in cytology.

Acetone Fixative

Organic solvent that rapidly dehydrates and precipitates proteins; favoured for frozen sections and immunostaining.

Cross-linking

Chemical bonding (often by aldehydes) between tissue proteins that stabilises structure during fixation.

Buffering

Use of phosphate, bicarbonate, or cacodylate solutions to keep fixatives at neutral pH and prevent acid artefacts.

Tissue-to-Fixative Ratio

Recommended volume proportion of ≥10 : 1 fixative to tissue to ensure adequate penetration.

Dehydration

Gradual replacement of tissue water with ascending alcohol concentrations after fixation.

Clearing

Substitution of alcohol with an organic solvent (e.g., xylene) that is miscible with paraffin wax and renders tissue transparent.

Xylene

Aromatic hydrocarbon used as the most common clearing agent prior to paraffin embedding.

Paraffin Wax

Solid hydrocarbon mixture that melts at 52–60 °C and provides external support during sectioning.

Vacuum Infiltration

Application of negative pressure to speed wax penetration while limiting heat-induced tissue damage.

Block Trimming

Removal of excess wax from the tissue block to create an ideal shape for microtomy and prevent dislodgement.

Microtome

Precision instrument that advances a wax block in controlled increments for reproducible thin sections.

Ribbon

Continuous strip of paraffin sections that adhere edge-to-edge after serial microtome cuts.

Water Bath Stretching

Placement of sections on warm water to eliminate wrinkles caused by wax compression during cutting.

Haematoxylin

Basic dye that, with a metal mordant, stains nuclei blue-purple by binding acidic nucleic acids.

Eosin

Acidic dye that stains cytoplasm, collagen, and extracellular proteins pink-red.

H&E Stain

Combination of haematoxylin and eosin; routine ‘gold-standard’ stain in diagnostic histology.

Periodic Acid-Schiff (PAS)

Special stain that colours carbohydrates, glycogen, and mucins magenta.

Masson’s Trichrome

Three-colour stain highlighting collagen (blue/green), muscle and cytoplasm (red/pink).

Giemsa Stain

Differential stain used on blood smears to visualise leukocytes and parasites; produces purple/blue hues.

Congo Red

Special stain that detects amyloid deposits, showing red colour and apple-green birefringence under polarised light.

Ziehl-Neelsen Stain

Acid-fast stain that identifies Mycobacteria by colouring them bright red against a blue background.

Prussian Blue

Histochemical stain that identifies ferric iron (hemosiderin) as bright blue granules.

Alcian Blue

Cationic dye that stains acidic mucins and glycosaminoglycans blue.

Silver Stains

Techniques using silver impregnation to visualise reticular fibres, basement membranes, and neuronal processes black.

De-waxing

Removal of paraffin with xylene before aqueous staining procedures.

DPX Mountant

Permanent resinous mounting medium composed of distrene, plasticiser, and xylene.

Formalin Pigment

Black-brown mercury-formaldehyde or acid formaldehyde heme precipitate formed in poorly buffered formalin.

Shrinkage Artefact

Reduction in tissue size caused by dehydration, leading to distorted morphology.

Overfixation

Excessively prolonged fixation that over-hardens tissue, complicating sectioning and interpretation.

Knife Marks

Parallel lines in sections resulting from a damaged or dirty microtome blade.

Chatter (Venetian Blind)

Rippled appearance in sections caused by vibration of the block during cutting.

Compression Folds

Wrinkles remaining in sections when wax cannot relax fully in the water bath.

Uneven Staining

Patchy colouration arising from inadequate washing, fixation, or inconsistent staining protocols.

Crystalline Precipitate

Microscopic crystals formed by dried stain that obscure tissue detail.

Air Bubble (Mounting Artefact)

Trapped air under the coverslip that distorts viewing and may displace tissue.