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Questions and Answers
What is the most popular histochemical technique for detecting free or conjugated carbohydrates?
PAS (Periodic Acid Schiff)
What color do nuclei appear as when stained with haematoxylin?
Globet cells are stained in pink with PAS histochemistry because of high content in __________.
mucopolysaccharides
Match the tissue necrosis pattern with its description:
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Acute inflammation is a non-specific response triggered in the surrounding tissue, designed to restore tissue to useful function.
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What is the purpose of impregnation and embedding media in histopathologic techniques?
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What are the four types of embedding media mentioned in the text?
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Over exposure of tissues to paraffin can cause tissue softening?
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What is the purpose of honing and stropping in histopathology tools maintenance? Badly nicked knives are sharpened to ensure optimal _____ of tissue blocks.
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Match the microtome types with their descriptions:
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What is the main purpose of staining in histopathology?
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Study Notes
Tissue Processing - Steps
- Impregnation/Infiltration: removing the clearing agent (xylene) completely and replacing it with a medium that fills all tissue cavities
- Purpose of impregnation: giving a firm consistency to the specimen, allowing easier handling and cutting of suitably thin sections without damage or distortion to the tissue and its cellular components
- Four types of embedding media: Paraffin wax, Celloidin, Gelatin, and Plastic
Paraffin Wax Impregnation
- Procedure: after clearing, the tissue is submerged in two or more changes of melted paraffin wax in an incubator/paraffin oven
- Temperature: between 55-60°C
- Laboratory temperature and wax melting points:
- 20-24°C: paraffin wax melting point of 54-58°C
- 15-18°C: paraffin wax melting point of 50-54°C
- Tissue characteristics and wax melting points:
- Hard tissues: wax with higher melting points
- Soft tissues: wax with lower melting points
Manual Impregnation by Paraffin Wax
- Procedure: multi-step process with 15-minute intervals
- Precautions in paraffin wax impregnation:
- Overexposure to paraffin can cause tissue hardening and shrinkage
- Overheated paraffin wax (above 60°C) can cause hardening and tissue shrinkage
- Paraffin wax must be pure, free from dust, water droplets, and other unwanted matter
- Alternative embedding media:
- Paraplast (melting point 56-57°C), more elastic and resilient than paraffin wax
- Embeddol (melting point 56-58°C), synthetic and less brittle than Paraplast
- Bioloid (semisynthetic wax used in embedding eyes)
- Ester wax (melting point 46-48°C), harder than paraffin wax, soluble in ethyl alcohol
- Carbowax (miscible with water)
Embedding
- Procedure: placing the tissue in a mold containing the embedding medium, allowing it to solidify
- Types of blocking-out molds:
- Consist of two L-shaped strips of heavy brass
- Compound embedding unit (series of interlocking plates on a flat metal/rubber base)
- Plastic embedding rings and base mold
- Disposable embedding molds (e.g. Peel-Away, plastic ice trays, paper boats)
Microtomy
- Definition: the process of trimming and cutting processed tissue into uniformly thin slices (sections) for microscope study
- Essential parts of a microtome:
- Block holder
- Knife carrier and knife
- Pawl, ratchet feed wheel, and adjustment screws
- Five kinds of microtomes:
- Rocking microtome (used for cutting sections of large blocks of paraffin-embedded tissues)
- Rotary microtome
- Sliding microtome (used for celloidin-embedded sections)
- Freezing microtome (used for unembedded frozen sections)
- Ultrathin microtome (used for cutting tissues in preparation for electron microscopy)
Microtome Knives
- Types:
- Plane concave knife
- Biconcave knife
- Plane wedge knife
- Honing and stropping:
- Reasons to sharpen the knife: jagged edges produce tears and striae in tissue sections
- Types of hones:
- Belgium yellow stone
- Arkansas stone
- Alumina stone
- Stropping procedure: uses a paddle strop with horse leather to remove burrs formed during honing and polish the cutting edge of the knife
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Description
Learn about the PAS staining technique used in histochemistry to detect carbohydrates in tissue samples. Understand how it works and its applications.
