Lec 15: Dehydration

Why?

To remove water from tissues, and to replace with other solution

Tissues contain much "free" water which does not mix well with the paraffin used later in the procedure. Thus it must undergo alcohol dehydration

Materials are to be embedded in paraffin to facilitate microtomy and Paraffin was insoluble in water (hydrophobic) interfere microtomy

Most of the stains are used as alcoholic solutions, present of water might interfere staining process

Techniques

specimens are dehydrated in a graded ethanol series from water through 10%-20%-50%-95%-100% ethanol

To prevent large outflow of water can damage the morphology of the cells and tissues

Duration of dehydration

Tissue blocks 1 mm thick should receive up to 30 minutes in each alcohol

blocks 5 mm thick require up to 90 minutes or longer in each change

Types of dehydrating agents

Ethanol, Methanol, Acetone, butyl alcohol

Procedures

1) 50 % ethanol

2) 70 % ethanol

3) 95 % ethanol

4) 100 % ethanol

Partial dehydration: avoid loosing too much lipid from specimen