Dr. Samah Kotb 2015 Histology Techniques CLS 322

 To understand what is Histology.  To understand the importance of Histology in medical field.  To recognize the normal microscopic features of all organs of human body.

 Histology is the science that tells about the normal microscopic feature of all the cells and tissues in the body.  Histology is the step before going to understand the pathology of diseased tissues.

To study the microscopic features of cells and tissues, the tissues are processed through various stages to be viewed under microscope, all these steps are called HISTOLOGICAL TECNIQUES OR PROCEDURES.

In the past manual methods were used; but histotechnology has now advanced to a paramedical science of automation and advanced techniques to help the pathologist in diagnosis. Histotechnologist should not only know what to do; but should also know the principle and the theory of what he or she is doing.

To Demonstrate such structures; the tissue must be prepared in such a way to allow microscopically observation and study of these different structures. This preparation includes the preservation of tissue materials, processing of tissue block, cutting and staining of thin sections.

1.Fixation2.Dehydration3.Embedding4.Cutting5.Staining These techniques are :

 Biological tissues must undergo a series of treatments to be observed with light and electron microscopes.  The process begins by stabilization of the tissue with chemical fixatives.  Next, the tissue is made rigid to allow sectioning.  Finally, it is stained to provide contrast for visualization in the microscope.

1.Fixation  Preserves cellular structure and maintains the distribution of organelles.  Formaldehyde the most commonly used chemical fixatives.

2.Dehydration The water is first extracted from the fragments by bathing them successively in a graded series of mixtures of ethanol and water, usually from 70% to 100% ethanol (dehydration).

 The liquid form of the embedding compound, for example, paraffin wax, replaces the intermediate solvent.  The liquid embedding medium is allowed to solidify, thereby providing rigidity to the tissue for sectioning. 3.Embedding

 The hard blocks containing the tissues are then placed in an instrument called a microtome and are sliced by the microtome's steel or glass blade into sections 1 to 10 micrometers thick. 4.Cutting

 To be studied microscopically sections must typically be stained or dyed because most tissues are colorless.  Methods of staining tissues have therefore been devised that not only make the various tissue components clear but also permit distinctions to be made between them. 5.Staining

There are various stains used to make histology slides, commonly used are the following: STAINTISSUES HaematoxylineStains nucleus of cell (blue) EosinStains cytoplasm of cell (pink) Masson’s trichome Stains connective tissue Wright’s stainStains blood cells Periodic acid Schiff(PAS) Stains basement membrane

Human body tissues are classified into four basic types. 1.Epithelial tissue 2.Connective tissue 3.Muscular tissue 4.Nervous tissue