Histotechnology Fixation and Dehydration

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Questions and Answers

What is the ideal location for fixation of a specimen after dissection?

  • At the site of removal (correct)
  • In a transport container
  • In a storage facility
  • In a laboratory setting

What should be done with specimens after dissection to ensure their integrity?

  • They should be fixed as soon as possible (correct)
  • They should be left out for observation
  • They can be stored at room temperature
  • They must be handled carelessly to avoid damage

What is a critical step after specimen dissection?

  • Transporting the specimen to a distant location
  • Fixation of the specimen should be delayed
  • Handling the specimen with care (correct)
  • Immediate disposal of the specimen

Why is it important to fix specimens promptly?

<p>To ensure accurate analysis and preservation (C)</p> Signup and view all the answers

What can occur if fixation is not properly handled after dissection?

<p>Damage to the specimen may occur (D)</p> Signup and view all the answers

What is a crucial requirement for reagents used in fixation?

<p>They must retain some chemical reactivity (B)</p> Signup and view all the answers

What is the primary purpose of using a liquid fixing agent like formaldehyde solution?

<p>To harden and preserve the tissue (A)</p> Signup and view all the answers

Why is it important for tissue components to retain chemical reactivity during fixation?

<p>To allow for specific staining techniques to be applied (A)</p> Signup and view all the answers

Which of the following best describes how formaldehyde solution interacts with tissue?

<p>It penetrates slowly, causing chemical and physical changes (A)</p> Signup and view all the answers

Which of the following can be considered unsuitable for fixation due to its properties?

<p>A reagent that alters tissue structure significantly (D)</p> Signup and view all the answers

What is a characteristic that fixation reagents must possess?

<p>They must be chemically reactive (D)</p> Signup and view all the answers

What happens to tissue after it is treated with a liquid fixing agent?

<p>It is permanently altered and preserved (D)</p> Signup and view all the answers

Which property of fixation reagents can directly impact staining results?

<p>Their retention of chemical reactivity (C)</p> Signup and view all the answers

Which step occurs immediately after applying a fixative like formaldehyde to tissue?

<p>Chemical and physical changes begin to occur (C)</p> Signup and view all the answers

Why is it important for a fixative to protect tissue during subsequent processing steps?

<p>To maintain the original form and structure of the tissue (B)</p> Signup and view all the answers

What is the primary purpose of using formalin in tissue preservation?

<p>To fix and preserve tissues for processing (C)</p> Signup and view all the answers

In what form is formalin typically used for tissue fixation?

<p>As a phosphate-buffered solution (B)</p> Signup and view all the answers

How long should specimens ideally remain in fixative?

<p>Long enough to ensure complete fixation (B)</p> Signup and view all the answers

What is one key characteristic of tissues that have been fixed in formalin?

<p>They remain structurally intact (A)</p> Signup and view all the answers

What should not be expected from specimens submerged in formalin?

<p>Immediate susceptibility to decay (A)</p> Signup and view all the answers

What is the primary purpose of substituting water with alcohol in the dehydration process?

<p>To preserve the structure of the specimen (B)</p> Signup and view all the answers

What is the correct concentration of ethanol used in the first step of the dehydration sequence for specimens up to 4mm thick?

<p>70% (D)</p> Signup and view all the answers

How long should a specimen be immersed in 100% ethanol during the dehydration process according to the typical sequence?

<p>15 minutes (B)</p> Signup and view all the answers

What is the order of the ethanol concentrations in the dehydration sequence for specimens not more than 4mm thick?

<p>70%, 90%, 100%, 100% (C)</p> Signup and view all the answers

Which concentration of ethanol is used for the second step in the dehydration process?

<p>90% (A)</p> Signup and view all the answers

What is the outcome after using ethanol for 45 minutes at 100% concentration?

<p>A tiny residue of tightly bound water is left. (B)</p> Signup and view all the answers

How long should ethanol be applied to effectively remove tightly bound water?

<p>45 minutes (D)</p> Signup and view all the answers

What concentration of ethanol was used for the removal of tightly bound molecular water?

<p>100% (A)</p> Signup and view all the answers

After using ethanol for 30 minutes, what state is the remaining water in the specimen?

<p>A mixture of bound and free water remains. (B)</p> Signup and view all the answers

What should be expected after treating a specimen with ethanol for a prolonged period?

<p>Reduction of free water but tightly bound water remains. (D)</p> Signup and view all the answers

Flashcards

Specimen Fixation

The process of preserving a biological specimen to prevent decay or decomposition.

Ideal Fixation Site

The best location for fixing a specimen is at the point of removal, such as an operating room.

Specimen Handling

Careful treatment of the biological specimen to maintain its integrity.

Timely Fixation

Fixing the specimen promptly after removal to prevent damage.

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Tissue Fixation

The process of preserving tissue using a chemical solution, hardening it and protecting it from further processing.

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Limited Fixation Reagents

A small set of chemicals used to preserve tissue samples, requiring specific properties to keep tissue reactive for staining.

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Tissue Reactivity

The ability of tissue components to undergo chemical reactions, which is crucial for staining.

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Fixative

A chemical solution that hardens and preserves tissue

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Fixation

The process of preserving tissues by stopping decomposition and making them suitable for staining and analysis.

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Formalin

A specific type of liquid fixing agent.

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Chemical Changes

Altering the tissue's structure at a molecular level during preservation.

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Staining Techniques

Methods used to highlight specific components in tissues using colored reagents.

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Physical Changes

Changes in the tissue's physical properties (e.g., hardening) due to the fixative.

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Formalin fixative

A common solution used to preserve tissues for later paraffin sectioning.

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Paraffin sections

Thin slices of tissue used for microscopic examination.

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Tissue preservation

The process of keeping tissues in a stable state for analysis.

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Fixative solution

A substance used for preserving tissues.

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Phosphate-buffered formalin

A buffered formalin solution used to preserve tissue samples.

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Specimen

A sample of tissue or biological material for examination or analysis.

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Ethanol Treatment (30 min)

A 100% ethanol solution is used for 30 minutes to remove water.

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Ethanol Treatment (45 min)

A 100% ethanol solution is used for 45 minutes to remove water.

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Removing Water Residue

The process is designed to remove almost all loosely-attached water from the specimen.

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Specimen Dehydration

A process where water in a specimen is gradually replaced with alcohol for preservation.

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Dehydration Sequence (4mm)

A step-by-step process using ethanol (alcohol) solutions of increasing concentrations (70%, 90%, 100%) to replace water in a specimen. Each step takes 15 minutes.

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Ethanol Percentage

Different concentrations of ethanol (alcohol) are used in the dehydration process.

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Ethanol Duration

Each ethanol solution step in the dehydration process is applied for 15 minutes.

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Specimen Thickness

The dehydration process is optimized for specimens less than or equal to 4mm thick.

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Study Notes

Histotechnology: Fixation and Dehydration

  • Specimen Acquisition: Fresh tissue specimens originate from various sources. They can be easily damaged during removal, so careful handling and prompt fixation are crucial. Ideal fixation occurs at the site of removal (e.g., operating theater) or immediately following.

Fixation

  • Purpose: Tissue specimens are placed in a liquid fixing agent (fixative) like formalin to cause chemical and physical changes hardening and preserving the tissue, protecting it from subsequent processing.

  • Fixative Selection: Only a limited number of reagents can be used for fixation, because the fixative must possess specific properties to be suitable. These properties ensure tissue preservation and chemical reactivity for subsequent staining procedures.

  • Formalin: Formalin (a phosphate-buffered solution) is the most commonly used fixative for paraffin sections.

  • Fixation Time: Specimens typically require between 6 to 24 hours of fixation to allow the fixative to penetrate all tissue components, and the chemical reactions to reach equilibrium.

Dehydration

  • Purpose: Melted paraffin wax is hydrophobic (water-resistant), so any water present must be removed from the specimen before infiltration with wax.

  • Method: Dehydration is commonly achieved by immersing the specimen in a series of increasing concentrations of ethanol (alcohol) solutions until pure, water-free alcohol is reached.

  • Ethanol's Properties: Ethanol is miscible with water. This ensures the water in the specimen is replaced progressively by the alcohol.

  • Dehydration Sequence: A common dehydration sequence for specimens not exceeding 4mm thick involves specific ethanol concentrations and time durations (e.g., 15 minutes in 70% ethanol, 90%, and later stages at 100% with increasing durations). This process aims to remove almost all of the water from the specimen.

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