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Match the following steps in histology with their descriptions:
Match the following steps in histology with their descriptions:
Fixation = Preserve the tissue and prevent structural change. Embedding = Supporting medium for tissue Sectioning = Cutting the tissue into thin slices Staining = Adding color to the tissue for examination
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Formalin = A mixture of formaldehyde gas and water Formaldehyde = A gas used in fixation Fixation = Preserving tissue from decay Autolysis = Breakdown of tissue by its own enzymes
Match the following materials with their uses:
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10% N.B.Formalin = Most common fixative in histology Methyl alcohol = Added to formaldehyde to make formalin Neutral buffer = Added to formalin to make it suitable for fixation Water = Used to dilute 100% formalin
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Match the following tasks with the role of an MLA in Histology/Cytology:
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Match the following types of cytology specimens with their descriptions:
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Study Notes
Histology
- The main function of a histology department is to prepare slides of tissue from various sources for pathologists to examine.
- Preparation of histological sections involves:
- Preservation of tissue through fixation to prevent structural changes.
- Embedding the tissue in a supporting medium.
- Sectioning the tissue.
- Staining the tissue.
Fixation
- Fixation is a critical step in histological section preparation to preserve tissue from decay.
- The most common fixative is 10% neutral buffered formalin.
- 10% neutral buffered formalin is cheap and penetrates tissue rapidly to preserve the natural state.
- Formalin is made by mixing 40% formaldehyde with 100ml of water.
Factors Affecting Fixation
- Temperature: Increasing the temperature of fixation increases the rate of diffusion of the fixative into the tissue and speeds up the rate of chemical reaction.
- Time: The longer the fixation, the better in most cases.
- Penetration rate: Depends on the fixative.
- Specimen dimensions: Optimal thickness is 1-4 mm.
Alternative Fixatives
- Bouin's solution: Contains picric acid.
- Zenker's fixative: Contains mercuric chloride.
- Glutaraldehyde: Used for electron microscopy.
- Alcohols: Good for cytology.
Gross Description
- The initial step in examining a clinical specimen.
- Produces two end products: a written document and a set of tissue blocks.
- The success of the final histological diagnosis depends on the skill of the professional performing the gross description.
Tissue Processing
- Dehydration: Removes water from the tissue using a series of alcohols (70%, 95%, 100%).
- Clearing: Uses an intermediate solvent to remove ethanol from the tissue.
- Wax infiltration: Infiltrates the tissue with a suitable histological wax.
Embedding
- Places the tissue in a mold with liquid embedding material, which is then hardened.
- Creates a stable block that can be cut into thin sections.
Microtomy
- Cuts sections of the tissue imbedded in the wax block using a microtome.
- Produces a series of ribbons at a thickness of 3-5 um.
Labelling Slides
- Labels slides with the same information as the block:
- Year
- S (if surgical specimen)
- Lab number
- Specimen number
- Sub number
Staining
- Most common stain is Hematoxylin and Eosin (H&E).
- Removes wax from the sections using a wax solvent.
- Hydrates the sections using descending alcohols and water.
- Stains the sections with H&E.
Permanent Mounting
- Dehydrates the slides with ascending alcohols and xylene.
- Covers the slides with a mountant and a glass coverslip.
- Removes excess mounting fluid using xylene.
Frozen Sections
- A rapid alternative to embedding in paraffin wax.
- Uses a cryostat to prepare and stain the tissue.
- Tissue is unfixed.
Cytology
- Definition: The study of cells in terms of structure, function, and chemistry.
- Objectives:
- Define cytology.
- List the three types of cytology specimens.
- Describe the different types of procedures used in cytology.
- Describe the most common stain used in cytology.
Types of Cytology Specimens
- Gynaecological: Cervical cancer demonstrates distinct pre-cancerous cellular changes.
- Non-gynaecological: Obtained from respiratory, urinary, or gastrointestinal systems.
- Fine needle aspirations: Obtained from various sites using a fine needle.
Stains Used in Cytology
- Papanicolaou stain: Used for gynecologic cytology and fixed non-gynecological samples.
- Romanowsky-type stain: Used for air-dried gynecologic preparations.
Specimen Preparation
- Methods:
- Cytocentrifugation preparation (Cytospin).
- ThinPrep preparation: Mainly used for cervical smears.
- Cell block preparation: Captures remaining specimen in the centrifuge tube.
Role of a Medical Laboratory Assistant (MLA) in Histology/Cytology
- Prepares specimens for histology and cytology.
- Labels tissue cassettes and slides.
- Performs routine tissue processor maintenance and reagent changes.
- Files and retrieves stained slides and paraffin blocks.
- Assists in the cutting room.
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Description
Learn the basics of histology, including the study of tissue, preparation of histological sections, and the role of the histology department.