Histopathology derive from the word histo and pathology. Histo means tissues while pathology indicates disease processes or changes. Before tissues are processed, they are pre-fixed in chemicals called fixatives. The specimens are sent in fixatives to the laboratory where they are registered and given histology number. This number is the laboratory number used for the processing of the specimen. Registered samples at Reception are transfered to the cut-up room for selection. Once part of the tissues are selected depending on the pathology presented, they are capped in tissue cassettes and transfered to the alcohol bath for processing starting from dehydration.
It is important to ensure that fixation is complete before tissue processing.
The aim of tissue processing is to embed the tissue in a solid medium firm to give support to the tissue to enable thin section to be cut and also soft to allow microtome blade to cut the sections. And the most embedding medium used in histopathology laboratory is paraffin wax.
DEHYDRATION
This is the first stage in tissue processing after proper fixation, it involves the removal of water from tissue, grades of alcohol are used, the concentration ranges from 70% alcohol to absolute alcohol, and tissue pass from 70% to absolute alcohol, tissue must be completely dehydrated before going into the next stage which is clearing to ensure the clearing agent and wax penetrate the tissue completely.
CLEARING
This is the next stage after dehydration, it involves removal of absolute alcohol and the replacing the processing solvent called xylene, which is miscible with both absolute alcohol and paraffin wax.
IMPREGNATION
Also called called infiltration, it involves the process of replacing the the xylene with molten paraffin wax.
EMBEDDING
Embedding is the process of placing the tissue in a embedding mould containing molten paraffin wax and it become solid when it is cold. This form solid support for tissue during microtomy on the microtome machine, it is important to properly orientate the tissue during embedding to ensure complete representation of all part of the tissue in the cut sections.
Tuesday, July 28, 2009
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