Histopathology 714434 162046389 2007-10-03T16:53:33Z El C 92203 Reverted edits by [[Special:Contributions/92.80.186.246|92.80.186.246]] ([[User talk:92.80.186.246|talk]]) to last version by Ozmaweezer '''Histopathology''' (from the Greek ''histos'' (tissue) and ''pathos'' (suffering)) refers to the [[light microscope|microscopic]] examination of tissue in order to study the manifestations of disease. Specifically, in clinical medicine, [[histopathology]] refers to the examination of a [[biopsy]] or surgical specimen by a [[pathology|pathologist]], after the specimen has been processed and [[histological section]]s have been placed onto glass slides. This is the most important tool of the [[anatomical pathology|anatomical pathologist]] in routine clinical [[diagnosis]] of [[cancer]] and other [[disease]]s. ==Collection of tissues== Histopathological examination of tissues starts with [[surgery]], [[biopsy]] or [[autopsy]]. The tissue is removed, and then placed in a [[fixation (histology)|fixative]] which stabilizes the tissues to prevent decay. The most common fixative is [[formalin]] (10% [[formaldehyde]] in water). ==Preparation for histology== The tissue is then prepared using [[histology]] procedures for viewing under a [[microscope]]. Briefly, the samples are transferred to a cassette, a container designed to allow reagents to freely act on the tissue inside. This cassette is immersed in multiple baths of progressively more concentrated [[ethanol]], to dehydrate the tissue, followed by [[toluene]] or xylene, 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 sample miscible with paraffin, a type of wax. This process is known as '''tissue processing'''. The processed tissue is then taken out of the cassette and set in a mold. Through this process of '''embedding''', additional paraffin is added to create a paraffin block which is attached to the outside of the cassette. The process of embedding then allows the [[sectioning]] of tissues into very thin (2 - 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. To see the tissue under a microscope, the sections are stained with one or more pigments. The aim of staining is to reveal cellular components; counterstains are used to provide contrast. The most commonly used stain in histopathology is a combination of [[hematoxylin]] and [[eosin]]. Hematoxylin is used to stain [[cell nucleus|nuclei]] blue, while eosin stains [[cytoplasm]] and the extracellular connective tissue matrix pink. There are hundreds of various other techniques which have been used to selectively stain cells. Other compounds used to color tissue sections include [[safranin]], [[Oil Red O]], [[congo red]], [[Silver compounds|silver salts]] and artificial dyes. '''Histochemistry''' refers to the science of using chemical reactions between laboratory chemicals and components within tissue. A commonly performed histochemical technique is the Perls Prussian Blue reaction, used to demonstrate iron deposits in diseases like [[Hemochromatosis]]. Recently, [[antibody|antibodies]] have been used to stain particular [[protein]]s, [[lipid]]s and [[carbohydrate]]s. Called [[immunohistochemistry]], this technique has greatly increased the ability to specifically identify categories of cells under a microscope. Other advanced techniques include '''in situ hybridization''' to identify specific [[DNA]] or [[RNA]] molecules. Digital cameras are increasingly used to capture histopathological images. ==Interpretation== The histological slides are examined under a microscope by a [[pathology|pathologist]], a medically qualified specialist. The diagnosis is formulated as a '''pathology report''' describing the histological findings and the opinion of the pathologist. In the case of [[cancer]], this represents the '''tissue diagnosis''' required for most treatment protocols. ==See also== * [[Histology]] * [[Pathology]] * [[Anatomical pathology]] * [[Biopsy]] * [[Frozen section procedure]] * [[Medical technologist]] ==External links== *[http://www.immunoportal.com Immunohistochemistry - In Situ Hybridization] *[http://www.pathol.uzh.ch/histologiekurs/ Virtual Histology Course - University of Zurich] (German, English version in preparation) {{pathology}} [[Category:Anatomical pathology]] [[Category:Histopathology| ]] [[nl:Histopathologie]] [[pl:Histopatologia]] [[ru:Патогистология]] [[sr:Хистопатологија]] [[th:มิญชพยาธิวิทยา]]