Histology
Histology, also known as microscopic anatomy, deals with the study of cells as they are constituted in the various tissue types. Single cells, isolated from the fabric of tissue, are generally difficult to classify. However, when cells are examined in their normal configuration and relationship to neighboring cells, the tissues formed by those cells are readily identified. A microscope is required because cells are microscopic and so too are the identifying characteristics of tissues.
While the body is structured of a bewildering array of organs, the number of tissue types is limited. Tissue types include epithelium, connective tissue, muscle, nervous tissue, blood and reproductive tissue. These categories include more than one type of tissue. For instance, connective tissue encompasses bone, cartilage, tendons, ligament, and fibrous connective tissue. Another example: the catagory muscle includes skeletal, cardiac and smooth.
The term microscopic anatomy is descriptive in that it indicates that tissue structure must be examined with a compound microscope. Because light does not penetrate thick masses of tissues and because tissue detail is revealed only by staining, it is necessary to process tissue in a somewhat elaborate manner for proper evaluation. A small fragment of tissue is cut and fixed (preserved). The fixative is chosen to maximize the retention of tissue structure. Dehydration follows fixation. This step removes water so that the tissue may be infiltrated with paraffin or a combination of paraffin and other waxes in preparation for sectioning. Frequently an intermediate step is required between dehydration and paraffin to enhance proper infiltration. The tissue in its paraffin block is now mounted on a microtome which is similar to a meat slicer but it can make slices of tissue routinely at 0.0001-0.0004 in (3-10 æm) thick. The slices of tissue are then mounted on a glass slide, the paraffin is removed, the tissue is stained, water is removed and a permanent mounting medium of the refractive index of glass is applied. Finally, a thin cover slip of glass is placed over the biopsy section. The microscopic slide is now ready for examination.
Histopathology uses knowledge of histology to evaluate tissues that may be malignant (cancerous) or otherwise abnormal. A lump is biopsied by a physician. A trained pathologist, a medical doctor who specializes in diagnosis of disease, will examined the biopsy. The tissue may be either normal or it may display varying degrees of pathological change. The histological diagnosis by the pathologist determines if further treatment is required. Physicians, because of time constraints, have devised short cuts that permit rapid examination of tissues. However, there is no short cut for microscopic examination of the biopsied tissue. Despite the explosion of biochemistry and molecular biology, pathologists still rely on microscopic examination of suspected malignant tissue.
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