Fixatives for Nervous Tissue

Questions and Answers

Which fixative is specifically noted for its effective use in histochemistry and electron microscopy?

Glutaraldehyde (correct)

Cajol's Formol Ammonium Bromide

Baker's Formol Calcium

Mercuric Chloride

What is the primary purpose of using 5% sodium thiosulfate in the fixation process?

To remove excess iodine (correct)

To fix proteins in the tissue

To enhance tissue preservation

To accelerate dehydration of tissues

Which of the following is true about Baker's Formol Calcium?

It requires a longer fixation time than glutaraldehyde.

It is effective for preserving lipids. (correct)

It contains mercuric chloride as a key ingredient.

It is primarily used for nervous tissue fixation.

What is the typical fixation time range for glutaraldehyde?

½ - 2 hours Signup and view all the answers

Which component is crucial for removing excess iodine during the dezenkerization process?

Sodium thiosulfate Signup and view all the answers

In the context of fixatives, what role does alcoholic iodine serve?

It's a primary fixative for acid mucopolysaccharides. Signup and view all the answers

What is the primary benefit of using glutaraldehyde in histopathological preparations?

It provides optimal protein cross-linking. Signup and view all the answers

What combination is necessary for preparing the alcoholic iodine solution for fixation?

0.5% iodine in 96% alcohol Signup and view all the answers

What is a significant characteristic of Ethanol/Ethyl Alcohol as a dehydrating agent?

It is the best dehydrating agent for routine use. Signup and view all the answers

Which dehydrating agent is noted for causing less shrinkage and hardening?

Butanol/Butyl Alcohol Signup and view all the answers

What is the primary disadvantage of using Methanol/Methyl Alcohol?

It is a toxic dehydrating agent. Signup and view all the answers

Which of the following is true about Isopropanol/Isopropyl Alcohol?

It is used when good-grade ethyl alcohol is not available. Signup and view all the answers

Which characteristic makes Benzene effective for urgent biopsies?

It is rapid acting with a clearing time of 15-60 minutes. Signup and view all the answers

What indicates the purity requirement for Ethanol in tissue processing?

It should be at least 99.7% pure. Signup and view all the answers

What is a common characteristic of clearing agents like acetone and xylene?

They should not be toxic to the body. Signup and view all the answers

What kind of hazard should not be present in tissue processing agents?

They should not be a fire hazard. Signup and view all the answers

What is the primary purpose of direct staining?

To give color to the sections using dye solutions Signup and view all the answers

Which component is essential in the process of indirect staining?

Mordant Signup and view all the answers

What type of tissue affinity do acidic cellular components generally have?

Greater affinity for basic dyes Signup and view all the answers

What is a primary disadvantage of using carbon tetrachloride as a clearing agent?

It produces tissue hardening. Signup and view all the answers

What role does mordant play in tissue staining?

It enhances the staining reaction by linking dye and tissue Signup and view all the answers

What is the purpose of using two contrasting stains during microscopic examination?

To facilitate clearer identification of morphological details Signup and view all the answers

Which of the following best describes tetrahydrofuran (THF)?

It dehydrates and clears at the same time. Signup and view all the answers

What is one of the main uses for methyl benzoate and methyl salicylate?

As slow-acting clearing agents for double embedding techniques. Signup and view all the answers

What is silver nitrate primarily used for in histology?

For silver staining of nervous system components Signup and view all the answers

Which statement best represents the quality of clove oil as a clearing agent?

It can be adulterated, leading to inconsistent quality. Signup and view all the answers

How does impregnation relate to tissue staining methods?

It incorporates heavy metal salts in visible tissues Signup and view all the answers

What characterizes a tissue-dye complex formed by the mordant?

A colored 'lake' that enhances visibility Signup and view all the answers

What is a characteristic of the impregnation process in tissue processing?

It completely removes the clearing agent from tissues. Signup and view all the answers

Which of the following tissues is vacuum embedding recommended for?

Urgent biopsies and delicate tissues. Signup and view all the answers

Which property distinguishes carbon tetrachloride from benzene?

Carbon tetrachloride is NOT carcinogenic. Signup and view all the answers

Which is a notable property of clove oil in tissue processing?

It effectively removes aniline dyes. Signup and view all the answers

Which method is primarily used for overstating nuclei in tissue samples?

Eosin-Methylene Blue (EMB) method Signup and view all the answers

What is a primary advantage of using the Hematoxylin-eosin method?

It is the most common method for microanatomical studies. Signup and view all the answers

Which component is critical in fixing tissue samples for staining?

Zenker's fluid Signup and view all the answers

Which staining method is recommended for sections needing resistance to strong alkaline or acid solutions?

Alcoholic Pinacyanol method Signup and view all the answers

What is the purpose of coating slides with dilute celloidin solutions?

To firmly attach sections to the slides Signup and view all the answers

Which reagent is critical in demonstrating tissue components containing glycogen?

Thionine Signup and view all the answers

What problem should be avoided when staining with cellulose nitrate?

Clearing stained sections with absolute alcohol Signup and view all the answers

What is the main focus of rapid metachromatic staining of frozen sections?

To differentiate among tissue components clearly Signup and view all the answers

Study Notes

Special Formalin Fixatives

0.5% iodine in 70% ethanol (alcoholic iodine): Used for 5-10 minutes followed by water and 5% sodium thiosulfate to remove excess iodine.
Cajol's Formol Ammonium Bromide: Effective fixative for nervous tissue (like astrocytes), requires washing in running water after decolorization.
Baker's Formol Calcium: Preserves lipids; most formalin fixatives damage lipids.
Addition of Iodine: Saturated iodine solution in 96% alcohol is used in later stages to decolorize iodine with absolute alcohol.

Glutaraldehyde

Fixation Time: Ranges from ½ to 2 hours; optimal for histochemistry and electron microscopy.
Composition: Contains two formaldehyde residues linked by three carbon chains, is effective for protein cross-linking.
Solution Concentration: 2.5% for small fragments; 4% for larger tissues.

Mercuric Chloride Fixatives

Should not harden tissues excessively and must retain stain.
Safety Considerations: Non-toxic and non-carcinogenic; useful in preserving tissue structure without brittleness.

Alcohol Fixatives

Ethanol (Ethyl Alcohol): Most effective, fast-acting dehydrating agent; should be at least 99.7% pure.
Methanol (Methyl Alcohol): Toxic, used for blood and tissue films.
Butanol (Butyl Alcohol): A slow dehydrating agent that produces less shrinkage.
Isopropanol (Isopropyl Alcohol): Alternative when high-grade ethyl alcohol is unavailable.

Clearing Agents

Benzene: Rapid-acting; used for urgent biopsies, clears alcohol without excessive brittleness.
Carbon Tetrachloride: Dangerous upon inhalation, produces hardening but cheaper alternative to chloroform.
Clove Oil: Expensive, unsuitable for routine use, removes aniline dyes and makes tissues brittle.
Tetrahydrofuran (THF): Dehydrates and clears simultaneously; miscible in water and paraffin.
Methyl Benzoate/Salicylate: Slow-acting clearing agents used for double embedding techniques.

Impregnation

Definition: Clearing agent removed, filling tissue to aid in diagnosis and morphology.
Techniques: Autotechnicon/Elliot-Bench Type Tissue Processor facilitates all steps.
Vacuüm Embedding: Recommended for urgent biopsies and delicate tissues by applying negative pressure.

Methods of Staining

Direct Staining: Color given using aqueous or alcoholic dye solutions (e.g., Methylene blue, Eosin).
Indirect Staining: Enhanced by mordants to promote dye attachment, e.g., Hematoxylin (basic) and Eosin (acid).
Silver Staining: Utilizes silver nitrate for impregnating nervous tissue.

Common Staining Techniques

Hematoxylin-Eosin Method: A key method for microanatomical studies; requires fixing in Zenker's fluid.
Colloidonization: Coats slides with dilute celloidin solutions to firmly attach sections.
Eye Dropper Method: Rapid metachromatic staining of frozen sections either on wet slides or solidified sections.

Final Notes

Preparation for Acidic vs Basic Dyes: Acidic tissues have greater affinity for basic dyes, and vice versa.
Care with Celloidin: Soluble in absolute alcohol, should be avoided during the dehydration and clearing of stained sections.

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Description

This quiz explores special fixatives such as 0.5% iodine in ethanol and formalin ammonium bromide used for preserving nervous tissue. Understand the application and effectiveness of these reagents in histology. Ideal for students studying biology and histopathology.