Histology (from the Greek ἱστός = 'tissue') is the study of the microscopic anatomy of cells and tissues of plants and animals. It is performed by examining a thin slice of tissue under a light microscope. The ability to visualize or differentially identify microscopic structures is frequently enhanced through the use of histological stains. Histology is an essential tool of biology and medicine.
Histopathology, the microscopic study of diseased tissue, is an important tool in anatomical pathology, since accurate diagnosis of cancer and other diseases usually requires histopathological examination of samples. Trained medical doctors, frequently board certified as Pathologists, are the personnel who perform histopathological examination and provide diagnostic information based on their observations.
The trained scientists who perform the preparation of histological sections are histotechnicians, histology technicians (HT), histology technologists (HTL), medical scientists, medical laboratory technicians, or biomedical scientists. Their field of study is called histotechnology.
Embedding can also be accomplished using frozen, non-fixed tissue in a water-based medium. Pre-frozen tissues are placed into moulds with the liquid embedding material, usually a water-based glycol or resin, which is then frozen to form hardened blocks.
Frozen tissue embedded in a freezing medium is cut on a microtome in a cooled machine called a cryostat.cell morphology. Hematoxylin and eosin (H&E) are the most commonly used stains in histology and histopathology. Hematoxylin colors nuclei blue; eosin colors the cytoplasm pink. To see the tissue under a microscope, the sections are stained with one or more pigments.
Special staining: There are hundreds of various other techniques that have been used to selectively stain cells and cellular components. Other compounds used to color tissue sections include safranin, oil red o, Congo red, fast green FCF, silver salts, and numerous natural and artificial dyes that were usually originated from the development dyes for the textile industry.
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.
Histology samples have often been examined by radioactive techniques. In historadiography a slide (sometimes stained histochemically) is X-rayed. More commonly, autoradiography is used to visualize the locations to which a radioactive substance has been transported within the body, such as cells in S phase (undergoing DNA replication) which incorporate tritiated thymidine, or sites to which radiolabeled nucleic acid probes bind in in situ hybridization. For autoradiography on a microscopic level, the slide is typically dipped into liquid nuclear tract emulsion, which dries to form the exposure film. Individual silver grains in the film are visualized with dark field microscopy.
Recently, antibodies are used to specifically visualize proteins, carbohydrates, and lipids: this is called immunohistochemistry, or when the stain is a fluorescent molecule, immunofluorescence. This technique has greatly increased the ability to identify categories of cells under a microscope. Other advanced techniques, such as nonradioactive in situ hybridization, can be combined with immunochemistry to identify specific DNA or RNA molecules with fluorescent probes or tags that can be used for immunofluorescence and enzyme-linked fluorescence amplification (especially alkaline phosphatase and tyramide signal amplification). Fluorescence microscopy and confocal microscopy are used to detect fluorescent signals with good intracellular detail. Digital cameras are increasingly used to capture histological and histopathological image
|Stain||Common use||Nucleus||Cytoplasm||Red blood cell (RBC)||Collagen fibers||Specifically stains|
|Haematoxylin||General staining when paired with eosin||Blue||N/A||N/A||N/A||Nucleic acids—blue Blue eER (ergastoplasm)—blue|
|Eosin||General staining when paired with haematoxylin||N/A||Pink||Orange/red||Pink||Elastic fibers—pink Reticular fibers—pink|
|Toluidine blue||General staining||Blue||Blue||Blue||Blue||Mast cells granules—purple|
|Masson's trichrome stain||Connective tissue||Black||Red/pink||Red||Blue/green||Cartilage—blue/green Muscle fibers—red|
|Mallory's trichrome stain||Connective tissue||Red||Pale red||Orange||Deep blue||Keratin—orange Cartilage—blue Bone matrix—deep blue Muscle fibers—red|
|Weigert's elastic stain||Elastic fibers||Blue/black||N/A||N/A||N/A||Elastic fibers—blue/black|
|Heidenhains'azan trichrome stain||Distinguishing cells from extracellular components||Red/purple||Pink||Red||Blue||Muscle fibers—red Cartilage—blue Bone matrix—blue|
|Silver stain||Reticular fibers, nerve fibers, fungi||N/A||N/A||N/A||Reticular fibers—brown/black Nerve fibers—brown/black|
|Wright's stain||Blood cells||Bluish/purple||Bluish/gray||Red/pink||N/A||Neutrophil granules—purple/pink Eosinophil granules—bright red/orange Basophil granules—deep purple/violet Platelet granules—red/purple|
|Orcein stain||Elastic fibres||Deep blue [or crazy red]||N/A||Bright red||Pink||Elastic fibres—dark brown Mast cells granules—purple Smooth muscle—light blue|
|Periodic acid-Schiff stain (PAS)||Basement membrane, localizing carbohydrates||Blue||N/A||N/A||Pink||Glycogen and other carbohydrates—magenta|
Table sourced fromMichael H. Ross, Wojciech Pawlina, (2006). Histology: A Text and Atlas. Hagerstown, MD: Lippincott Williams & Wilkins.
Note that tissues from plants, fungi, and microorganisms can also be examined histologically. Their structure is very different from animal tissues.
Artifacts are structures or features in tissue that interfere with normal histological examination. These are not always present in normal tissue and can come from outside sources. Artifacts interfere with histology by changing the tissues appearance and hiding structures. These can be divided into two categories:
2. Stedman's Medical Dictionaries (2005). Stedman's Online Medical Dictionary Retrieved 2005-01-26.
3. 4,000 online histology images (2007). (http://histology-online.com)