What is Fixation in Histology?
Fixation is a crucial step in
histology that preserves biological tissues from decay, thereby maintaining their structure and composition for microscopic examination. The primary goal is to stabilize the tissues to prevent autolysis and putrefaction, allowing for accurate and detailed analysis.
Why is the Duration of Fixation Important?
The duration of fixation is critical as it directly affects the quality of tissue preservation. Insufficient fixation can result in
autolysis or decomposition of cellular components, while over-fixation can lead to excessive cross-linking of proteins, making tissues hard and brittle. Both extremes can compromise the integrity of histological findings.
Type of fixative: Different fixatives have varying penetration rates and degrees of tissue hardening.
Tissue size and thickness: Larger or thicker tissues require longer fixation times for complete penetration.
Temperature: Fixation at higher temperatures generally accelerates the process, while lower temperatures slow it down.
Agitation: Gentle shaking or stirring can enhance fixative penetration and reduce fixation time.
Formalin: Typically, 6-24 hours. Formalin is the most commonly used fixative and offers good tissue preservation with minimal shrinkage.
Glutaraldehyde: Generally, 2-4 hours. It's often used for electron microscopy due to its ability to preserve fine cellular details.
Bouin's solution: Usually, 4-12 hours. It is particularly effective for preserving soft and delicate tissues.
Loss of cellular detail
Distortion of tissue morphology
Autolysis and bacterial contamination
On the other hand, over-fixation can lead to:
Excessive hardening of tissues
Difficulty in sectioning
Masking of antigenic sites, affecting
immunohistochemistry results
Referring to established protocols for specific tissues and fixatives
Conducting pilot studies on small tissue samples
Consulting scientific literature and expert recommendations
Microwave fixation: This technique uses microwave energy to accelerate fixation, significantly reducing the time required.
Vacuum fixation: Applying a vacuum can help fixatives penetrate tissues more effectively.
Automated tissue processors: These devices automate the fixation process, ensuring consistent and optimal fixation times.
Conclusion
The duration of fixation is a pivotal aspect of histological preparation, directly impacting the quality and reliability of tissue analysis. By understanding the factors that influence fixation and adhering to recommended protocols, researchers and pathologists can ensure accurate and meaningful histological results.
