Histopathology
From Freepedia
Histopathology is a field of pathology which specialises in the microscopic study of diseased tissue. It is an important tool of anatomical pathology and is used for accurate diagnosis of tumors and other diseases.
Histopathological examination of tissues starts with surgery, biopsy or autopsy. The tissue is removed, and then placed in a fixative which stabilizes the tissues to prevent decay. The most common fixative is formalin (10% formaldehyde in water).
The tissue is then prepared for viewing under a microscope. The samples are immersed in multiple baths of progressively more concentrated ethanol, to dehydrate the tissue, followed by toluene, and finally hot liquid paraffin. During this 12 to 16 hour process, paraffin will replace the water in the tissue, turning soft, moist tissues into a hard paraffin block. This process is known as embedding.
The process of embedding then allows the sectioning of tissues into very thin (5 - 7 micrometer) sections using a microtome. The microtome slices the tissue ready for microscopic examination. The slices are thinner than the average cell, and are layered on a glass slide for staining.
Because a slice of tissue is very thin (5 to 7 micrometers) it is almost completely transparent with very little visible detail. To see the tissue under a microscope, the sections are stained with one or more pigments.
Hematoxylin and eosin are among the most commonly used stains in histopathology. Hematoxylin is used to color nuclei blue, while eosin is used to color the cytoplasm pink. Other compounds used to color tissue sections include saffron, silver salts and artificial dyes. The science of tissue staining is called histochemistry.
Recently, antibodies are used to stain specific proteins: this is called immunohistochemistry. This technique has greatly increased the ability to identify categories of cells under a microscope. Other advanced techniques include in situ hybridization to identify specific DNA or RNA molecules, and confocal microscopy. Digital cameras are increasingly used to capture histopathological images.
