- The anatomical study of the microscopic structure of animal and plant tissues.
- The microscopic structure of tissue.
histologically his'to·log'i·cal·ly adv.
histologist his·tol'o·gist n.
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The study of the structure and chemical composition of tissues of animals and plants as related to their function. The primary aim is to understand how tissues are organized at all structural levels, including the molecular and macromolecular, the entire cell and intercellular substances, and the tissues and organs.
The four tissues of the animal body include cells and intercellular substances. They are (1) epithelium, in which the cells are generally closely applied to each other and separated by very little intercellular substance; (2) connective tissue, in which the cells are usually separated by greater amounts of intercellular substance, which may indeed form the great bulk of the tissue; (3) muscular tissue, whose cells are primarily concerned with contractility; and (4) nervous tissue, whose components are concerned primarily with rapid conduction of impulses. See also Connective tissue; Epithelium; Muscular system; Nervous system (vertebrate).
The major fields of histological studies are morphological descriptions; developmental studies; histo- and cytophysiology; histo- and cytochemistry; and (5) fine (or submicroscopic) structure.
Microanatomy, which is the microscopic study of normal tissue and organs at the cellular level.
For more information on histology, visit Britannica.com.
One who specializes in histology.
The histology examination showed how the cells were affected by the introduction of the medication.
Histology (from the Greek ἱστός) is the study of tissue sectioned as a thin slice, using a microtome. It can be described as microscopic anatomy. The photographing of stained cells is called histography. Histology is an essential tool of biology.
Histopathology, the microscopic study of diseased tissue, is an important tool of anatomical pathology since accurate diagnosis of cancer and other diseases usually requires histopathological examination of samples.
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.
Fixatives are used to preserve the tissue, the structures of the cell, and the cell organelles found in the individual cells (eg. nucleus, rough endoplasmic reticulum, mitochondria, and a lot more). The tissues are mechanically and biochemically stabilized in a fixative. The most common fixative is neutral buffered formalin (10% formaldehyde in Phosphate buffered saline (PBS)). It is important to consider that a fixative should not be too toxic to its handler, and it should not damage the tissue being preserved.
The most common technique is wax processing. The samples are immersed in multiple baths of progressively more concentrated ethanol to dehydrate the tissue, followed by a clearing agent such as, xylene or Histoclear, and finally hot molten paraffin wax (impregnation). During this 12 to 16 hour process, paraffin wax will replace the xylene:
Soft, moist tissues are turned into a hard paraffin block, which is then placed in a mold containing more molten wax (embedded) and allowed to cool and harden.
Embedding can also be accomplished using frozen, non-fixed tissue in a freezing medium. This freezing medium is liquid at room temperature but when cooled will solidify. Non-fixed tissue allows for procedures such as in-situ hybridizations for specific mRNA that would have been destroyed during the fixing process. It also allows for very short turnaround where that is needed, as with a patient currently undergoing surgery.
The tissue is then sectioned into very thin (2 - 8 micrometer) sections using a microtome. These slices, usually thinner than the average cell, are then placed on a glass slide for staining.
Frozen tissue embedded in a freezing medium is cut on a microtome in a cooled machine called a cryostat.
Routine staining:This is done to give contrast to the tissue being examined, as without staining it is very difficult to see differences in cell morphology. Hematoxylin and eosin (abbreviated 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 which 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 can be combined with this, such as nonradioactive in situ hybridization 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 images.
| 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 | 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 | N/A | Bright Red | Pink | Elastic fibres - Dark Brown
Mast cells granules - purple Smooth Muscle - Light Blue |
| Periodic acid-Schiff stain (PAS) | Basement Membrane, Localising carbohydrates | Blue | N/A | N/A | Pink | Glycogen and other Carbohydrates - Magenta |
Table sourced from Michael H. Ross, Wojciech Pawlina, (2006). Histology: A Text and Atlas. Hagerstwon, MD: Lippincott Williams & Wilkins. ISBN 0-7817-5056-3.
The Nissl method and Golgi's method are useful in identifying neurons.
Alternative techniques include cryosection. The tissue is frozen and cut
using a cryostat. 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
In the 19th century, histology was an academic discipline in its own right. The 1906 Nobel
Prize in Physiology or Medicine was awarded to the histologists, Camillo Golgi and
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).
Note that tissues from plant, fungus and microorganisms can also be examined histologically. Their structure is very different from animal tissue.
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:
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.
Artifacts can result from tissue processing. Processing commonly lead 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 Bouin's fixative to fix a section.
1. Merck Source (2002). Dorland's Medical Dictionary. Retrieved 2005-01-26.
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)
| Histology: epithelial tissue | |
|---|---|
| Types | Columnar (simple, stratified) - Cuboidal (simple, stratified) - Pseudostratified/Respiratory - Squamous (simple, stratified) - Transitional - Olfactory |
| Features | Lateral/cell-cell: Tight junction - Adherens junction - Desmosome - Gap
junction Basal/cell-matrix: Basal lamina - Hemidesmosome - Focal adhesion Apical: Cilia - Microvilli - Stereocilia |
| Histology: connective tissue | |
|---|---|
| Classification | proper (loose/areolar, dense, adipose brown and white, reticular) embryonic (mucous, mesenchymal) specialized (cartilage, bone, blood) |
| Extracellular matrix | ground substance (tissue fluid) fibers (collagen, reticular fiber, elastic fibers) |
| Cells | resident (fibroblast, adipocyte, chondroblast, osteoblast), wandering cell |
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Dansk (Danish)
n. - histologi, vævslære
Nederlands (Dutch)
weefselleer
Français (French)
n. - histologie
Deutsch (German)
n. - Histologie (Lehre von den Körpergeweben)
Ελληνική (Greek)
n. - (ιατρ.) ιστολογία
Português (Portuguese)
n. - histologia (f) (Med.)
Español (Spanish)
n. - histología
Svenska (Swedish)
n. - histologi (läran om kroppens vävnader)
中文(简体) (Chinese (Simplified))
组织学
中文(繁體) (Chinese (Traditional))
n. - 組織學
العربيه (Arabic)
(الاسم) علم الانسجه, علم يبحث في الانسجه العضويه, مؤلف في علم الانسجه, البنيه النسيجيه
עברית (Hebrew)
n. - תורת ריקמות-הגוף, תורת מבנה הרקמות
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