wikademia>Eme: /* External links */

2010-04-03T22:07:21Z

External links

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	== External links ==		== External links ==
	~~{{commons cat\|Histology}}~~		* [http://www.ihcworld.com/protocol_database.htm Histology Protocols]
	*[http://www.ihcworld.com/protocol_database.htm Histology Protocols]		* [http://www.kumc.edu/instruction/medicine/anatomy/histoweb Histoweb]
	*[http://www.kumc.edu/instruction/medicine/anatomy/histoweb Histoweb]		* [http://www.siumed.edu/%7Edking2/index.htm SIU SOM Histology]
	*[http://www.siumed.edu/%7Edking2/index.htm SIU SOM Histology]		* [http://www.visualhistology.com/Visual_Histology_Atlas/ Visual Histology Atlas]
	*[http://www.visualhistology.com/Visual_Histology_Atlas/ Visual Histology Atlas]		* [http://www.histology-world.com/glossary/glossary1.htm Histology Glossary]
	*[http://www.histology-world.com/glossary/glossary1.htm Histology Glossary]		* [http://www.hgv.org.au Histology Group of Victoria Incorporated]
	*[http://www.hgv.org.au Histology Group of Victoria Incorporated]		* [http://www.histology-world.com/photoalbum/ Histology Photomicrographs]
	*[http://www.histology-world.com/photoalbum/ Histology Photomicrographs]		* [http://www.path.uiowa.edu/virtualslidebox Virtual Slidebox]
	*[http://www.path.uiowa.edu/virtualslidebox Virtual Slidebox]		* [http://www.lab.anhb.uwa.edu.au/mb140/ Blue Histology]
	*[http://www.lab.anhb.uwa.edu.au/mb140/ Blue Histology]		* [http://www.histologyfordummies.com Histology for Dummies (Spanish)]
	*[http://www.histologyfordummies.com Histology for Dummies (Spanish)]

	~~{{Epithelial tissue}}~~
	~~{{Connective tissue}}~~
	~~{{Muscle tissue}}~~
	~~{{Nervous tissue}}~~

	[[Category:Medical terms]]		[[Category:Medical terms]]

wikademia>Eme at 22:06, 3 April 2010

2010-04-03T22:06:42Z

← Older revision		Revision as of 22:06, 3 April 2010
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	~~{{Refimprove\|date=March 2009}}~~
	[[Image:Microscope with stained slide.jpg\|right\|thumb\|300px\|A stained histologic specimen, sandwiched between a glass [[microscope slide]] and coverslip, mounted on the stage of a light microscope.]]		[[Image:Microscope with stained slide.jpg\|right\|thumb\|300px\|A stained histologic specimen, sandwiched between a glass [[microscope slide]] and coverslip, mounted on the stage of a light microscope.]]
	[[Image:Emphysema H and E.jpg\|right\|300px\|thumb\|Microscopic view of a histologic specimen of human [[lung]] tissue stained with [[hematoxylin]] and [[eosin]].]]		[[Image:Emphysema H and E.jpg\|right\|300px\|thumb\|Microscopic view of a histologic specimen of human [[lung]] tissue stained with [[hematoxylin]] and [[eosin]].]]
	'''Histology''' ~~(compound of the [[Greek language\|Greek]] words: ''{{polytonic\|[[wiktionary:ἱστός\|ἱστός]]}}'' "tissue", and -''[[wiktionary:λογία\|λογία]]'' [[wiktionary:-logia\|-logia]])~~ is the study of the [[anatomy\|microscopic anatomy]] of [[cell (biology)\|cells]] and [[tissue (biology)\|tissues]] of [[plants]] and [[animals]]. It is performed by examining a thin slice (section) of tissue under a [[light microscope]] or [[electron 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]].		'''Histology''' is the study of the [[anatomy\|microscopic anatomy]] of [[cell (biology)\|cells]] and [[tissue (biology)\|tissues]] of [[plants]] and [[animals]]. It is performed by examining a thin slice (section) of tissue under a [[light microscope]] or [[electron 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\|board-certified]] as [[Pathologist]]s, are the personnel who perform histopathological examination and provide diagnostic information based on their observations.		''[[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\|board-certified]] as [[Pathologist]]s, are the personnel who perform histopathological examination and provide diagnostic information based on their observations.

wikademia>Eme: from http://en.wikipedia.org/wiki/Histology

2009-11-21T19:55:19Z

from http://en.wikipedia.org/wiki/Histology

New page

{{Refimprove|date=March 2009}}
[[Image:Microscope with stained slide.jpg|right|thumb|300px|A stained histologic specimen, sandwiched between a glass [[microscope slide]] and coverslip, mounted on the stage of a light microscope.]]
[[Image:Emphysema H and E.jpg|right|300px|thumb|Microscopic view of a histologic specimen of human [[lung]] tissue stained with [[hematoxylin]] and [[eosin]].]]
'''Histology''' (compound of the [[Greek language|Greek]] words: ''{{polytonic|[[wiktionary:ἱστός|ἱστός]]}}'' "tissue", and -''[[wiktionary:λογία|λογία]]'' [[wiktionary:-logia|-logia]]) is the study of the [[anatomy|microscopic anatomy]] of [[cell (biology)|cells]] and [[tissue (biology)|tissues]] of [[plants]] and [[animals]]. It is performed by examining a thin slice (section) of tissue under a [[light microscope]] or [[electron 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|board-certified]] as [[Pathologist]]s, 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 Assistant|medical laboratory technicians]], or [[biomedical scientist]]s. Their field of study is called ''histotechnology.''

==Technical procedure==
===Fixation===
====Chemical Fixation with Formaldehyde or Other Chemicals ====
{{main|Fixation (histology)}}
Chemical fixatives are used to preserve tissue from degradation, and to maintain the structure of the cells inclusive of sub-cellular components such as cell organelles (e.g., nucleus, endoplasmic reticulum, mitochondria). The most common fixative for light microscopy is 10% neutral buffered formalin (4% [[formaldehyde]] in [[phosphate buffered saline]]). For electron microscopy, the most commonly used fixative is [[glutaraldehyde]], usually as a 2.5% solution in [[phosphate buffered saline]]. These fixatives preserve tissues or cells mainly by irreversibly cross-linking proteins. The main action of these aldehyde fixatives is to cross-link amino groups in proteins through the formation of CH<sub>2</sub> ([[methylene]]) linkage, in the case of formaldehyde, or by a C5H10 cross-links in the case of glutaraldehyde. This process, while preserving the structural integrity of the cells and tissue can damage the biological functionality of proteins, particularly [[enzymes]], and can also [[Denaturation (biochemistry)|denature]] them to a certain extent. This can be detrimental to certain histological techniques. Further fixatives are often used for electron microscopy such as [[osmium tetroxide]] or [[uranyl acetate]]

====Frozen Section Fixation ====
[[Frozen section]] is a rapid way to fix and mount histology sections. It is used in surgical removal of [[tumors]], and allow rapid determination of margin (that the tumor has been completely removed). It is done using a refrigeration device called a [[cryostat]]. The frozen tissue is sliced using a [[microtome]], and the frozen slices are mounted on a glass slide and stained the same way as other methods. It is a necessary way to fix tissue for certain stain such as antibody linked [[immunofluorescence]] staining.

=== Processing - Dehydration, Clearing and Infiltration===
The aim of Tissue Processing is to remove water from tissues and replace with a medium that solidifies to allow thin sections to be cut. Biological tissue must be supported in a hard matrix to allow sufficiently thin sections to be cut, typically 5 μm (micrometres; 1000 micrometres = 1 mm) thick for light microscopy and 80-100 nm (nanometre; 1,000,000 nanometres = 1 mm) thick for electron microscopy. For light microscopy, paraffin wax is most frequently used. Since it is immiscible with water, the main constituent of biological tissue, water must first be removed in the process of dehydration. Samples are transferred through baths of progressively more concentrated [[ethanol]] to remove the water, followed by a clearing agent, usually [[xylene]], to remove the alcohol, and finally molten [[paraffin wax]], the infiltration agent, which replaces the xylene.
Paraffin wax does not provide a sufficiently hard matrix for cutting very thin sections for electron microscopy. Instead, resins are used. Epoxy resins are the most commonly employed embedding media, but acrylic resins are also used, particularly where [[immunohistochemistry]] is required. Thicker sections (0.35μm to 5μm) of resin-embedded tissue can also be cut for light microscopy. Again, the immiscibility of most epoxy and acrylic resins with water necessitates the use of dehydration, usually with ethanol.

===Embedding===
After the tissues have been dehydrated, cleared and infiltrated with the embedding material they are ready for external embedding. During this process the tissue samples are placed into moulds along with liquid embedding material (such as agar, gelatine or wax) which is then hardened. This is achieved by cooling in the case of paraffin wax and heating in the case of the epoxy resins (curing). The acrylic resins are polymerised by heat, ultraviolet light or chemical catalysts. The hardened blocks containing the tissue samples are then ready to be sectioned.

Formalin-fixed, paraffin-embedded (FFPE) tissues may be stored indefinitely at room temperature, and nucleic acids (both DNA and RNA) may be recovered from them decades after fixation, making FFPE tissues an important resource for historical studies in medicine.

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, OCT, TBS, Cryogel or resin, which is then frozen to form hardened blocks.

===Sectioning===
For light microscopy, a glass knife mounted in a [[microtome]] is used to cut 10-[[micrometre|micrometer]]-thick tissue sections which are mounted on a glass [[microscope slide]]. For transmission electron microscopy, a diamond knife mounted in an [[ultramicrotome]] is used to cut 50-[[nanometre|nanometer]]-thick tissue sections which are mounted on a 3-[[millimeter]]-diameter copper grid. Then the mounted sections are treated with the appropriate [[staining (biology)|stain]].

Frozen tissue embedded in a freezing medium is cut on a microtome in a cooled machine called a [[cryostat]].

===[[Staining (biology)|Staining]]===
Biological tissue has little inherent contrast in either the light or electron microscope. Staining is employed to give both contrast to the tissue as well as highlighting particular features of interest. Where the underlying mechanistic chemistry of staining is understood, the term [[histochemistry]] is used. [[Hematoxylin]] and [[eosin]] (H&E) is the most commonly used light microscopical stain in histology and histopathology. Hematoxylin, a basic dye, stains [[cell nucleus|nuclei]] blue due to an affinity to nucleic acids in the cell nucleus; eosin, an acidic dye, stains the [[cytoplasm]] pink. Uranyl acetate and lead citrate are commonly used to impart contrast to tissue in the electron microscope.

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 [[dye]]s 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 camera]]s are increasingly used to capture histological and histopathological image

== Common laboratory stains ==

{| class="wikitable"
|-
! 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
|-
Fungi—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 from {{cite book |author=Michael H. Ross, Wojciech Pawlina, |title=Histology: A Text and Atlas |publisher=Lippincott Williams & Wilkins |location=Hagerstown, MD |year=2006 |pages= |isbn=0-7817-5056-3 |oclc= |doi=}}

The [[Nissl method]] and [[Golgi's method]] are useful in identifying [[neuron]]s.

===Alternative techniques===
Alternative techniques include [[frozen section procedure|cryosection]]. The tissue is frozen using a [[cryostat]], and cut. Tissue staining methods are similar to those of wax sections. Plastic embedding is commonly used in the preparation of material for electron microscopy. Tissues are embedded in [[epoxy]] resin. Very thin sections (less than 0.1 micrometer) are cut using diamond or glass knives. The sections are stained with electron dense stains (uranium and lead) so that they can possibly be seen with the [[electron microscope]].

==History==
In the 19th century, histology was an academic discipline in its own right. The 1906 [[Nobel Prize]] in Physiology or Medicine was awarded to histologists [[Camillo Golgi]] and [[Santiago Ramon y Cajal]]. They had dueling interpretations of the neural structure of the brain based in differing interpretations of the same images. Cajal won the prize for his correct theory and Golgi for the staining technique he invented to make it possible.

==Histological classification of animal tissues==
There are four basic types of tissues: muscle tissue, nervous tissue, connective tissue, and epithelial tissue. All tissue types are subtypes of these four basic tissue types (for example, blood cells are classified as connective tissue, since they generally originate inside bone marrow).

*[[Epithelium]]: the lining of glands, bowel, skin and some organs like the liver, lung, kidney
*[[Endothelium]]: the lining of blood and lymphatic vessels
*[[Mesothelium]]: the lining of pleural and pericardial spaces
*[[Mesenchyme]]: the cells filling the spaces between the organs, including fat, muscle, bone, cartilage, and tendon cells
*[[Blood cell]]s: the red and white blood cells, including those found in lymph nodes and spleen
*[[Neurons]]: any of the conducting cells of the nervous system
*[[Germ cell]]s: reproductive cells ([[spermatozoa]] in men, [[oocyte]]s in women)
*[[Placenta]]: an organ characteristic of true mammals during pregnancy, joining mother and offspring, providing endocrine secretion and selective exchange of soluble, but not particulate, blood-borne substances through an apposition of uterine and trophoblastic vascularised parts
*[[Stem cell]]s: cells able to turn into one or several of the above types

Note that tissues from plants, fungi, and microorganisms can also be examined histologically. Their structure is very different from animal tissues.

==Related sciences==

*[[Cell biology]] is the study of living cells, their DNA and RNA and the proteins they express.
*[[Anatomy]] is the study of [[organ (anatomy)|organs]] visible by the naked eye.
*[[Morphology (biology)|Morphology]] studies entire organisms.

==Artifacts==

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:

====Pre-histology====
These are features and structures that have being introduced prior to the collection of the tissues. A common example of these include: ink from tattoos and freckles (melanin) in skin samples.

====Post-histology====
Artifacts can result from tissue processing. Processing commonly leads to changes like shrinkage, color changes in different tissues types and alterations of the structures in the tissue. Because these are caused in a laboratory the majority of post histology artifacts can be avoided or removed after being discovered. A common example is mercury pigment left behind after using [[Zenker's fixative]] to fix a section.

== See also ==
* [[Pathology]]
* [[Anatomical pathology]]
* [[Histopathology]]
* [[Staining (biology)|Biological staining]]
* [[Digital Pathology]]
* [[List of publications in biology#Histology|Important publications in histology]]
* [[Geoffrey Bourne (anatomist)|Geoffrey Bourne]]
* [[Laser capture microdissection]]

== References ==
1. Merck Source (2002). [[Dorland's Medical Dictionary]]. Retrieved 2005-01-26.

2. Stedman's Medical Dictionaries (2005). [http://stedmans.com/ Stedman's Online Medical Dictionary]. Retrieved 2005-01-26.

3. 4,000 online histology images (2007). (http://histology-online.com)

== External links ==
{{commons cat|Histology}}
*[http://www.ihcworld.com/protocol_database.htm Histology Protocols]
*[http://www.kumc.edu/instruction/medicine/anatomy/histoweb Histoweb]
*[http://www.siumed.edu/%7Edking2/index.htm SIU SOM Histology]
*[http://www.visualhistology.com/Visual_Histology_Atlas/ Visual Histology Atlas]
*[http://www.histology-world.com/glossary/glossary1.htm Histology Glossary]
*[http://www.hgv.org.au Histology Group of Victoria Incorporated]
*[http://www.histology-world.com/photoalbum/ Histology Photomicrographs]
*[http://www.path.uiowa.edu/virtualslidebox Virtual Slidebox]
*[http://www.lab.anhb.uwa.edu.au/mb140/ Blue Histology]
*[http://www.histologyfordummies.com Histology for Dummies (Spanish)]

{{Epithelial tissue}}
{{Connective tissue}}
{{Muscle tissue}}
{{Nervous tissue}}

[[Category:Medical terms]]
[[Category:Physiology]]
[[Category:Histology]]
[[Category:Subjects taught in medical school]]
[[Category:Greek loanwords]]

About histology - Revision history

wikademia>Eme: /* External links */

wikademia>Eme at 22:06, 3 April 2010

wikademia>Eme: from http://en.wikipedia.org/wiki/Histology