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2014-05-13 Tissue Processing
Histology is the study of the microscopic structure of tissues.  The study of pathological cells is known as Histopathology.  By identifying morphological changes in tissues, it is possible to see characteristics of certain diseases.

Steps in Tissue Processing:
1. Fixation
2. Embedding
    * Dehydration
    * Clearing
==>>2a. Tissue Microarray
3. Sectioning
4. Mounting
5. Dewaxing

-To preserve tissue archetecture, tissue must first be fixed.  
-Chemical reagents are used to hold tissue components in their normal places during the subsequent processing. -They also prevent tissue from rotting and auto-digestion by leaked lysosomes.  
-Fixatives have binding sites to form cross links between adjacent tissue proteins (this is how they preserve tissue).  
-Microbes bind to spare binding sites and are deactivated, this is how tissues are portected from microbial attach.  
-Fixative only proseve proteins.

-Embedding tissues provides them with physical support so tissue can be sectioned thinly.
-The process involves hardening the tissues by replacing the water with resin or wax.
-Neither was nor resin are miscible with water however, so water is gradually replaced with alcohol in the process called dehydration.
-Once tissue has been dehydrated, it can then go through a process called clearing.
-As wax and resin are not miscible with alcohol either, the alcohol is replaced with a organic substance called xylene and the tissue goes transparent.
-Finally the solvent is replaced with hot molten wax (58.C) with is cooled to harden.
-The dehydration process can damage and alter tissue.
-The clearing process dissolves alcohol and lipids as well.