Please enable JavaScript.

Coggle requires JavaScript to display documents.

Lec 14: Fixation (Characteristic of a good fixative (Does not alter…

- - - - May cause protein clot
      - Can alter the tissues
      - Infrequently used
  - - - Good for enzyme related works; does not denature proteins and enzymes
      - Preserve cells and tissues
      - Suitable for histochemical studies
      - Rapid processing - can provide immediate diagnostic information to a surgeon in the operating room
    - - requires special equipment (cryotome) for sectioning
      - usually produces thicker sections (8+ micrometers) resulting in loss of resolution
      - produces greater distortion of tissue in cutting
      - tissue degrades with thawing (become soft)
  - - - thinner sections (2 – 8+ micrometers)
    - - loss of fat and most enzyme and protein function
      - antibody binding sites (epitopes) lost
    - - Perfusion
        
        involves the delivery of fixative through the circulatory system of living tissue, by direct injection into a major artery
      - Immersion
        
        Successful fixation by immersion requires very small samples
    - - 10% Formalin
        
        cross-link membrane proteins by forming covalent bonds (hardens it)
        
        Advantages: It penetrates rapidly, causes little distortion, does not destroy any of the cellular constituents and can be followed by almost all staining methods
        
        Disadvantages: It hardens the tissues very slowly. However, it does not protect them from the shrinking agents employed in embedding and sectioning
      - Osmium
        
        Advantages: preserves the cell in a form closer to the living than any other fixativ
        
        Disadvantages: it penetrates poorly and cannot be followed by many stains.
        
        standard fixative for electron microscopy.
        
        also used as a stain because it blackens fat and various lipid-containing