Histopathology Fixation Techniques

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the primary purpose of fixation in histopathology?

To facilitate the growth of microorganisms

To enhance the color of tissues

To stimulate enzymatic activity in cells

To preserve tissue morphology and prevent degradation (correct)

Which of the following is NOT a function of a fixative?

Facilitate staining process

Preserve cell in a living state

Prevent autolysis

Enhance tissue respiration (correct)

Which type of fixative is most commonly used in routine histopathology labs?

Acid coagulation fixative

Dehydrating coagulation fixative

Physical fixative

Chemical fixative (correct)

What does a coagulation fixative primarily disrupt in order to maintain tissue morphology?

Proteins Signup and view all the answers

How do dehydrating coagulation fixatives affect protein structure?

They disrupt the tertiary structure of proteins Signup and view all the answers

Which coagulation fixative specifically coagulates nucleic acids?

Acetic acid Signup and view all the answers

What type of fixative primarily uses heat or freezing methods?

Physical fixative Signup and view all the answers

Which characteristic is common among all types of chemical fixatives?

They maintain adequate morphological preservation Signup and view all the answers

What pH level does picric acid create when dissolved in water?

pH 2.0 Signup and view all the answers

What is the primary function of neutral buffered formalin (NBF) in histopathology?

To fix tissues by forming bonds between proteins Signup and view all the answers

What is a common consequence of prolonged fixation in acidic formalin?

Formation of formalin pigment Signup and view all the answers

Which type of formalin is most commonly used in histopathology labs due to its better tissue preservation?

Neutral buffered formalin Signup and view all the answers

Which of the following is a safety measure when using formaldehyde?

Wear PPE such as gloves and goggles Signup and view all the answers

What effect does formaldehyde have on proteins and nucleic acids?

Forms cross-links between them Signup and view all the answers

What is the typical concentration of formaldehyde in 10% neutral buffered formalin?

4% formaldehyde Signup and view all the answers

Which statement about the use of formalin in histopathology is true?

Formalin can cause respiratory irritation Signup and view all the answers

Study Notes

Fixation in Histopathology

Fixation preserves tissue by hardening it and preventing the loss of tissue molecules.
Appropriate tissue fixation is crucial for all histology tests.
Without fixation, tissues degrade, and analysis becomes impossible.
Fixation maintains clear and consistent morphological features.

Function of Fixatives

Prevent autolysis (enzyme breakdown of tissue).
Prevent putrefaction (microorganism breakdown of tissue).
Preserve cells in a live-like state.
Protect tissue from damage during processing.
Aid in staining processes.
Minimize diffusion of soluble molecules.

Types of Fixatives

Physical fixatives:
- Use heat, microwave, or freeze-drying.
- Not routinely used in practical histopathology.
Chemical fixatives:
- Most frequently used in histopathology labs.
- Involve using liquid fixatives.

Chemical Fixatives: Categories

Coagulant fixatives:
- Use organic or non-organic solutions to coagulate proteins, making them insoluble.
- Cellular architecture mainly maintained by lipoproteins and collagen.
- Protein coagulation maintains tissue histomorphology at the light microscope level..

Coagulation Fixatives: Subtypes

Dehydrating coagulant fixatives:
- Remove water from the tissue by breaking down hydrophobic bonds in the protein structure.
- Disruption of tertiary protein structure (denaturation) which changes their physical properties and potentially renders them insoluble.
- Examples: ethanol, methanol.
Acid coagulant fixatives:
- Use acids like picric acid and acetic acid to disrupt electrostatic and hydrogen bonds.
- Can insert lipophilic anions into hydrophilic regions.
- Disrupt the tertiary structures of proteins.
- Acetic acid coagulates nucleic acids but not proteins and added to other fixatives to prevent nucleic acid loss.

Cross-Linking Fixatives

Several chemicals are selected for their potential to form cross-links between proteins and within nucleic acids and proteins.

Formaldehyde

10% neutral buffered formalin (NBF): The most common fixative in diagnostic pathology.
Pure formaldehyde, a vapor, when dissolved in water creates formalin (37-40% formaldehyde solution)
- The typical 10% formalin used in tissue fixation only has approximately 4% weight-to-volume formaldehyde.
Formaldehyde is effective in preserving tissue morphology, preventing degradation, and maintaining cellular structure by forming bonds.
Suitable with stains like H&E, IHC, and ISH.
Types of Formalin:
- Acidic formalin: pH below 7 (typically 4-5).
  - Less frequently used.
  - Prolonged fixation can lead to formalin pigment, especially in blood-rich tissue.
  - May impact staining quality.
- Neutral buffered formalin (NBF): neutral pH (typically 7.0).
  - Minimizes pigment formation and improves tissue preservation.
  - Compatible with a range of histological and molecular techniques.
Safety Precautions (Formalin)
- All formalin types are carcinogenic, respiratory irritants, and skin sensitizers.
- Use proper ventilation, personal protective equipment (PPE), and store in sealed containers.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz explores the essential role of fixation in histopathology, focusing on its function, types, and categories of fixatives. Learn how fixation preserves tissues and prevents degradation, ensuring accurate histological analysis. Test your understanding of both physical and chemical fixatives used in laboratory settings.