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What is a characteristic feature of formaldehyde as a fixative?
Which fixative is ideal for tissues containing iron pigments?
What is a major downfall of using 10% Formol-saline as a fixative?
What is the typical fixation time required for formalin?
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Which of the following statements about formal-corrosive is true?
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What happens to the positivity of mucin to PAS after fixation with 10% Neutral Buffered Formalin?
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What is a common use for 10% Formol-saline?
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Why is formaldehyde considered an irritating fixative?
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Which aldehyde fixative is known for enhancing immunoperoxidase studies on tissues after post-fixation?
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What is a distinguishing characteristic of glutaraldehyde compared to formaldehyde?
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What is the main disadvantage of using mercuric chloride as a fixative?
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Which metallic fixative is particularly recommended for fixing the pituitary gland and blood-containing organs?
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What is the primary use of potassium dichromate in tissue fixation?
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For which type of tissues is Bouin's Solution particularly effective?
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What is a key factor that enhances the fixation process of tissues?
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Which fixative is known to destroy xenobiotic substances in tissues?
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Which metallic fixative is known for producing excellent results in glycogen demonstration?
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What characteristic does trichloroacetic acid exhibit when used as a fixative?
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What is one of the main applications of microwave fixation?
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What effect does using glacial acetic acid have on tissues?
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What describes the fixation process of Carnoy's Fluid?
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What is the primary purpose of fixation in histotechnology?
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Which type of fixation incorporates the chemical constituent of the fixative into the tissue?
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Which of the following is NOT a factor involved in fixation?
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What effect do fixatives have on tissue during processing?
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Which of the following characteristics is essential for a good fixative?
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Which type of fixative is designed to preserve specific cell parts and their microscopic structures?
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What is an important practical consideration for fixation related to duration?
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Which of the following fixatives is classified as a non-additive fixative?
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What is the result of a fixative acting as a mordant?
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What is a typical mechanism behind additive fixation?
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Which of these is an additive fixative?
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What is an effect of using poor fixation techniques in histotechnology?
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In the context of fixation types, what does physical fixation involve?
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Study Notes
Histotechnology Overview
- Histotechnology aids pathologists in diagnosing diseases through high-quality tissue sections.
- Fresh tissues are primarily examined for immediate evaluation, preservation, staining, and long-term storage.
Tissue Processing Steps
- Fixation: Preserves tissue integrity and morphology.
- Dehydration, Clearing, Infiltration, Embedding, Trimming, Section-cutting, Staining, Mounting, Labeling.
Fixation Importance
- First and fundamental step in histotechnology.
- Ensures quality tissue for diagnosis; prevents degeneration and distortion.
- Stabilizes proteins to maintain cellular structure.
Fixation Mechanisms
- Additive fixation incorporates fixative into tissue, forming cross-links (e.g., Formalin, Mercury).
- Non-additive fixation alters tissue without incorporation, mainly through dehydration (e.g., Alcohol).
Factors Affecting Fixation
- Hydrogen ion concentration influences fixation efficacy.
- Temperature and section thickness can affect the outcome.
- Osmolality, concentration, and duration are critical for optimal fixation.
Practical Considerations in Fixation
- Speed and penetration are essential for effective fixation.
- The volume of fixative and fixation duration affects tissue quality.
Effects of Fixatives
- Harden and ease handling of soft tissues.
- Make cells resistant to solutions that cause damage.
- Inhibit bacterial decomposition and improve optical differentiation for staining.
Characteristics of Good Fixatives
- Cost-effective, stable, and safe for handling.
- Must rapidly kill cells and minimize tissue shrinkage while ensuring penetration.
Types of Fixation
- Physical Fixation: Heating, Microwave, Freezing.
- Chemical Fixation: Classified by composition and action.
Fixatives by Composition
- Simple Fixatives: E.g., Formaldehyde, Alcohol.
- Compound Fixatives: E.g., Picric Acid, Mercuric Chloride, Osmium Tetroxide.
Fixatives by Action
- Micro-anatomical Fixatives: Preserve overall tissue structure without altering intercellular relationships.
- Cytological Fixatives: Focus on specific cell structures, including nuclear and cytoplasmic components.
Aldehyde Fixatives
- Formaldehyde: Commonly used as 4% solution (10% formalin) with a fixation time of 24 hours. Preserves fats and does not over-harden tissues.
- 10% Formol Saline: Ideal for post-mortem tissues, preserves enzymes, and tends to shrink tissues.
- 10% Neutral Buffered Formalin: Best for iron-containing tissues and requires no post-treatment.
- Formal-Corrosive: Recommended for routine examination; excellent penetration and staining quality.
Cytological Fixatives
- Nuclear Fixative: Preserves nuclear structures with glacial acetic acid.
- Cytoplasmic Fixative: Preserves cytoplasmic structures without acetic acid.
- Histochemical Fixative: Maintains chemical constituents of cells and tissues.### Aldehyde Fixatives
- Alcohol Formalin (Gendre’s): Rapid fixation used for sputum; partial lysis of RBC, poor preservation of iron pigments.
- Glutaraldehyde: Composed of two formaldehyde residues; stable, preserves plasma proteins, recommended for enzyme histochemistry, and electron microscopy; slower tissue penetration, may increase brittleness.
- Glutaraldehyde is buffered with osmium tetroxide for better electron microscopy results; varying fixation times based on tissue size.
Metallic Fixatives
- Mercuric Chloride: Common secondary fixative; poor penetration but rapid tissue hardening; produces black precipitates; excellent for trichrome staining, particularly in renal and connective tissues.
- Zenker’s Fluid: Contains mercuric chloride and acetic acid; effective for small tissues like liver and spleen.
- Helly’s Solution: Great for pituitary and bone marrow, preserves cytoplasmic granules.
- Heidenhain’s Susa Solution: Ideal for tumor biopsies; fixation time ranges from 3-12 hours.
- B-5 Fixative: Commonly used for bone marrow biopsies.
Chromate Fixatives
- Chromic Acid: Strong oxidizing agent used as a protein precipitant, preserves carbohydrates.
- Potassium Dichromate: Preserves lipids and mitochondria; used at pH 4.5-5.2.
- Regard’s (Muller’s) Fluid: Recommended for chromatin and mitotic figures; fixates poorly, darkens over time.
- Orth’s Fluid: Preserves myelin better; useful for degenerative processes and bacteria.
Lead Fixatives
- Lead Fixatives: Used as a 4% solution of basic lead acetate; effective for acid mucopolysaccharides and connective tissue mucin.
Picric Acid Fixatives
- Picric Acid: Saturated solution that dyes tissues; excellent for glycogen, not suitable for frozen sections.
- Bouin’s Solution: Recommended for embryos and pituitary biopsies; preserves delicate structures effectively.
Glacial Acetic Acid
- Used with other fixatives; precipitates nucleoprotein; induces tissue swelling; not for cytoplasmic fixation.
Alcohol Fixatives
- Ethanol: Concentrations of 70-100%; simple fixative for blood and tissue films; can lyse RBC.
- Isopropyl Alcohol: Used for touch preparations and special staining procedures.
- Carnoy’s Fluid: Rapid (5 hours) and effective for chromosome fixation.
Osmic Acid Fixatives
- Osmium Tetroxide: Strong oxidizing solution fixes lipids; yields brilliant nuclear staining for ultrathin sectioning.
- Flemming’s Solution: Commonly used for nuclear preparation; poor penetration, forms artifact pigments.
Other Fixatives
- Heat Fixation: Rapid method for bacterial smears; produces significant shrinkage.
- Secondary Fixation: Aids in demonstrating specific substances; improves tissue preservation.
Washing-Out Procedures
- Essential post-fixation to remove excess fixatives, using specific methods for different fixative types.
Factors Affecting Fixation
- Retarding Factors: Tissue size, the presence of mucus, fat, or blood, and cold temperatures.
- Enhancing Factors: Agitation and specific tissue thickness.
Fixation Artifacts
- Acid conditions may create artifacts; buffered formalin reduces these issues.
Microwave Technique
- Physical method to accelerate fixation; effective for neurochemical preservation; reduces fixation time significantly; limitations include shallow penetration and effects on protein cross-linking.
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Description
This quiz covers the fundamental concepts of histotechnology, including the art and science of producing quality tissue sections. It discusses the importance of tissue processing and the reasons for examining fresh tissues. Gain insight into this essential field that aids in disease diagnosis.
