Histological Techniques

Histology is the study of the cellular organization of body tissues and organs. The structure of cells and tissues can be distinguished at two levels. The fine structure is that which can be distinguished at the level of light microscopy (a magnification of 1000 x or less). Electron microscopes are generally employed to study ultrastructure B the detailed structure of the cell cytoplasm, organelles and membranes that is not discernable with a light microscope. Cell structure is most commonly studied in slices of the tissue, called sections, that are thin enough to allow transmission of light or an electron beam. There are many methods of sectioning tissues, and sometimes particular tissues require special techniques. The method most widely employed is called the paraffin method.

THE PARAFFIN METHOD all histological procedures can be divided into a similar series of steps. For the paraffin method these steps are as follows: I. Tissue resection II. Fixation iii. Dehydration IV. Infiltration and embedding in paraffin V. Sectioning with a microtome VI. Mounting on microscope slides VII. Clearing and staining VIII. Preparation of permanent mounts

Once the tissue is removed from the patient, it has to be immediately fixed by putting it into adequate amount of 10% formaldehyde (10% formalin) before sending it to the pathologist. The purposes of fixation are: prevent autolysis and putrefaction (bacterial decomposition). Preserve tissue details as nearly as possible to living state. Hardening the tissue by coagulating proteins. Renders the tissue receptive to subsequent staining. Prevent damage during subsequent procedure.

The tissue is processed by putting it into different chemicals The tissue is processed by putting it into different chemicals. It is then impregnated (embedded) in paraffin, sectioned (cut) into thin slices, & is finally stained.

The stains can be hematoxylin/eosin stain or special stains such as PAS, immunohistochemistry, etc... The hematoxylin/eosin stain is usually abbreviated as h&e stain. The H&E stain is routinely used. It gives the nucleus a blue color & the cytoplasm & the extracellular matrix a pinkish color.