Lecture 2 - From Specimen to Report I Flashcards
What is the purpose of a biopsy in histology?
A biopsy involves the removal of tissue for histological assessment, aiming to examine cellular structures for diagnostic purposes.
What are the three types of tissue degeneration?
Abnormal metabolism, autolysis (cellular degradation), and putrefaction (bacterial/fungal contamination) are the three types of tissue degeneration.
How does fixation prevent tissue degradation, and what are the characteristics of a good fixative?
Fixation blocks enzyme activity by chemicals or heat, aiming to kill cells evenly, penetrate tissues, prevent autolysis/putrefaction, and not add extraneous material or alter cell size.
Explain the mechanisms of fixation, specifically the cross-linking process.
Formaldehyde (HCHO) is a common fixative that forms methylene bridges between proteins, creating a gel matrix. This cross-linking is advantageous for preserving tissues.
What are the advantages and disadvantages of formaldehyde as a fixative?
Advantages include slow, reversible fixation and cost-effectiveness. Disadvantages include toxicity, potential carcinogenicity, and artefacts.
Name alternative fixatives and their specific applications.
Glutaraldehyde for electron microscopy, mercuric chloride for bright staining, osmium tetroxide for lipid fixation, alcohols for cytopathology, and acetic acid for preserving chromosome morphology.
What factors affect the fixation process, and why is fixation important?
Factors include temperature, specimen type, volume, concentration, and duration. Fixation preserves tissues for further processing and analysis.
What is the role of labeling and data entry in the histological process?
Labeling involves unique identification through barcodes, and data entry ensures accurate specimen information is recorded in the Laboratory Information Management System (LIMS).
How is tissue graded during grossing/cut up, and what does grade A signify?
Tissue is graded from A to E based on dissection needs. Grade A signifies no dissection is needed, and the sample is transferred intact into a processing cassette.
Why is decalcification necessary, and what are the agents used for decalcification?
Decalcification is needed for hard tissues like bones and teeth. Agents include acid decalcifiers and chelating agents, which remove calcium phosphate.
How is tissue processing achieved, and what are the three stages involved?
Tissue processing converts tissues into supported blocks for cutting thin sections. The three stages are dehydration, clearing, and impregnation with wax.
Describe the dehydration stage in tissue processing.
Dehydration involves replacing water in tissues with alcohol, using graded series such as 70%, 90%, and 100% ethanol.
What are the considerations in selecting a clearing agent, and name common clearing agents?
Considerations include speed, toxicity, flammability, and effect on tissues. Common clearing agents include xylene and hist-clear (limonene).
Explain the impregnation stage in tissue processing.
Impregnation includes multiple baths of molten wax to ensure complete penetration. The wax must match the hardness of tissues for smooth sectioning.
Why is tissue processing important, and how is it typically performed?
Tissue processing is vital for converting tissues into sections suitable for microscopy. It is often automated overnight, but manual processing may occur due to specific circumstances.
