FIXATION

FIXATION

1. FUNCTION: preserving fresh tissue for examination

   • PRIMARY AIM: to preserve the morphologic and chemical integrity of the cell
   • SECONDARY AIM: to harden and protect the tissue

2. MECHANISMS

   • ADDITIVE FIXATION - chemical constituent is taken in and becomes part of the tissue (Ex. formalin, mercuric fixatives, osmium tetraoxide)
   • NON-ADDITIVE - removing bound water (ex. alcohol)

3. FACTORS INVOLVED

   • 1. Hydrogen ion concentration - satisfactory fixation = pH 6.8
   • 2. Temperature
     • Surgical spx - RT (22-25c); electron microscopy and some histochem - 0-4c
     • Formalin heated @60c - very urgent biopsy specimenS
       • Formalin heated @100c - for TB
   • 3. Thickness of section 4. Osmolality 5. Concentration 6. Duration of Fixation

4. GENERAL EFFECTS of fixatives

   • Tissue Hardenen - hardens soft and friable tissues
   • Cell Protector - resistant to damage
   • Bacetrial inhibiitor - prevents tissuedecay
   • Stain enhancer - acts as a mordant/accentuator
   • Optical differentiator - optical differentiation
   • INfection control - reduction of risk of infections