Microtechniques

Def: Preparation of histologic sections from tissues for microscopic examination >> The ideal micro-technique that preserves structural relations between cells as in living tissue

 

Paraffin Technique for L.M >> Fresh small tissue samples [1cm] are obtained >> Steps: 1-Fixation: in formalin → Preserve tissue structure 2-Dehydration: in ascending grades of alcohol [50%, 70%, 90% then in 100%] → Removes all water. 3-Clearing: Alcohol is removed in chemical solvents [xylol] → Tissue becomes translucent 4-Infiltration: Tissue is placed in melted paraffin until it becomes completely infiltrated 5-Embedding: Paraffin-infiltrated tissue is placed in a small container with melted paraffin and allowed to harden. 6-Trimming: Paraffin block is trimmed to expose the tissue for sectioning on a microtome. 7-Sectioning: The trimmed hard paraffin block is fixed on a holder and cut into thin sections [3-10 µm] by sharp metal knife in a device called [Microtome]

Advantages of Paraffin Technique >> Rapid technique >> Gives serial sections for research >> Gives thin section easily stained 

Disadvantages: >> Xylol dissolves fat content, so cannot be demonstrated >> The heat destroys enzymes of the cell, so cannot demonstrate chemical components

 N.B: Microtechniques for preparation of a tissue sample for electron microscopic examination differ in some points: 1. Tissue samples are smaller 2. Fixation: in Formalin + Glutaraldehyde 3. Embedding: in Epoxy resin to give harder tissue 4. Sectioning: Very thin sections < 1 µm by glass or diamond knife