Fixation Flashcards
What are the methods of fixation?
- Heat
- Freezing
- Chemically
These methods are used to preserve biological tissues for examination.
What is the purpose of fixation?
- Stabilize proteins
- Protect tissue from subsequent damage
- Harden the tissue
- Preserve life-like state of tissue
Fixation is crucial for maintaining the integrity of biological samples.
How does fixation work?
- Prevents autolysis (enzyme degradation)
- Prevents putrefaction (bacterial decomposition)
- Stabilizes proteins
- Increases visibility and contrast (RI = 1.54)
The refractive index (RI) indicates how light interacts with the tissue.
What are the qualities of an ideal fixative?
- Rapid penetration
- Kills tissue quickly
- Hardens tissue slightly for easier cutting
- Non-toxic
An ideal fixative minimizes damage to the tissue while preserving its structure.
What are major fixatives used in tissue preservation?
- Aldehyde
- Alcohols
- Mercurials
- Oxidizing agents
- Picrate’s
Each fixative has unique properties and applications in histology.
What is the fixative of choice for most applications?
NBF (Neutral Buffered Formalin)
NBF is widely used due to its effectiveness and compatibility with various staining techniques.
What factors affect fixation?
- Temperature
- Size
- Volume (20:1)
- Time
- Fixation of choice
- Penetration
- Storage
- pH
- Osmolality
These factors influence the quality and effectiveness of the fixation process.
What are sources of error in fixation?
- Insufficient fixation
- Improper ratio of fixative to tissue
- Poor penetration (wrong fixative used)
- Tissue not suspended (not exposed from all sides)
- Insufficient time in fixative (mushy)
Errors during fixation can lead to compromised tissue integrity and artifacts.
What are common artifacts that can occur during fixation?
- Protein precipitation
- Autolysis / desquamation
- Putrefaction
- Diffusion / substance loss
- Shrinkage
- Distortion
- Excess hardening
- Formalin pigment (brown)
- Mercuric pigment (brown)
Artifacts can significantly impact the interpretation of histological samples.
What is the difference between coagulant and non-coagulant fixatives?
Coagulant: harsh denaturation of proteins, better penetration, forms a meshwork due to shrinkage
Non-Coagulant: gentler denaturation, preferred, additive fixation
The choice between coagulant and non-coagulant fixatives can affect tissue morphology.
What are additive vs non-additive fixatives?
Additive: chemically links to the tissue; common feature of all primary fixing agents except ethanol
Non-Additive: does not combine with tissue; coagulates proteins by dehydrating them
Understanding the mechanism of each type of fixative is crucial for selecting the appropriate one for specific applications.
Fill in the blank: The only fixative that acts as a non-additive fixative is _______.
Ethanol
Ethanol’s unique properties make it different from other fixatives.
