Histology

Source: Wikipedia, the free encyclopedia.
"Histography" redirects here. For the study of history as a science, see Historiography.
Histologic specimen being placed on the stage of an optical microscope
hematoxylin and eosin
as seen under a microscope

Histology,[help 1] also known as microscopic anatomy or microanatomy,

cytology, the study of cells, modern usage places all of these topics under the field of histology.[5] In medicine, histopathology is the branch of histology that includes the microscopic identification and study of diseased tissue.[5][6] In the field of paleontology, the term paleohistology refers to the histology of fossil organisms.[7][8]

Biological tissues

Animal tissue classification

Main article: Anatomy § Animal tissues

There are four basic types of animal tissues:

epithelial tissue.[5][9] All animal tissues are considered to be subtypes of these four principal tissue types (for example, blood is classified as connective tissue, since the blood cells are suspended in an extracellular matrix, the plasma).[9]

Plant tissue classification

Histologic section of a plant stem (Alliaria petiolata)
Main article:
Plant Anatomy

For plants, the study of their tissues falls under the field of plant anatomy, with the following four main types:

Medical histology

pathologists
, perform histopathological examination and provide diagnostic information based on their observations.

Occupations

The field of histology that includes the preparation of tissues for microscopic examination is known as histotechnology. Job titles for the trained personnel who prepare histological specimens for examination are numerous and include histotechnicians, histotechnologists,[11] histology technicians and technologists, medical laboratory technicians, and biomedical scientists.

Sample preparation

Most histological samples need preparation before microscopic observation; these methods depend on the specimen and method of observation.[9]

Fixation

Main article: Fixation (histology)
bryozoan
.

Chemical

phosphate buffered saline).[13][12][9]

For electron microscopy, the most commonly used fixative is

phosphate buffered saline.[9] Other fixatives used for electron microscopy are osmium tetroxide or uranyl acetate.[9]

The main action of these

enzymes
.

Formalin fixation leads to degradation of mRNA, miRNA, and DNA as well as denaturation and modification of proteins in tissues. However, extraction and analysis of nucleic acids and proteins from formalin-fixed, paraffin-embedded tissues is possible using appropriate protocols.[14][15]

Selection and trimming

Items used for submitting specimens: (Biopsy) wrap, (biopsy) sponge, (tissue processing) cassette and (biopsy) bag.

Selection is the choice of relevant tissue in cases where it is not necessary to put the entire original tissue mass through further processing. The remainder may remain fixed in case it needs to be examined at a later time.

Trimming is the cutting of tissue samples in order to expose the relevant surfaces for later sectioning. It also creates tissue samples of appropriate size to fit into cassettes.[16]

Embedding

Tissues are embedded in a harder medium both as a support and to allow the cutting of thin tissue slices.[9][5] In general, water must first be removed from tissues (dehydration) and replaced with a medium that either solidifies directly, or with an intermediary fluid (clearing) that is miscible with the embedding media.[12]

Paraffin wax

Histologic sample being embedded in paraffin wax (Tissue is held at the bottom of a metal mold, and more molten paraffin is poured over it to fill it.)

For light microscopy,

miscible with the wax, finally melted paraffin wax is added to replace the xylene and infiltrate the tissue.[9] In most histology, or histopathology laboratories the dehydration, clearing, and wax infiltration are carried out in tissue processors which automate this process.[13] Once infiltrated in paraffin, tissues are oriented in molds which are filled with wax; once positioned, the wax is cooled, solidifying the block and tissue.[13][12]

Other materials

Paraffin wax does not always provide a sufficiently hard matrix for cutting very thin sections (which are especially important for electron microscopy).

celloidin, and other types of waxes.[12][17]

In electron microscopy epoxy resins are the most commonly employed embedding media,[9] but acrylic resins are also used, particularly where immunohistochemistry is required.

For tissues to be cut in a frozen state, tissues are placed in a water-based embedding medium. Pre-frozen tissues are placed into molds with the liquid embedding material, usually a water-based glycol, OCT, TBS, Cryogen, or resin, which is then frozen to form hardened blocks.

Sectioning

Main article: Microtome
Histologic sample being cut on a microtome

For light microscopy, a knife mounted in a microtome is used to cut tissue sections (typically between 5-15

ultramicrotome is used to cut between 50 and 150 nanometer thick tissue sections.[9]

A limited number of manufacturers are recognized for their production of microtomes, including vibrating microtomes commonly referred to as

vibratomes, primarily for research and clinical studies. Additionally, Leica Biosystems is known for its production of products related to light microscopy in the context of research and clinical studies.[18]

Staining

Main article: Staining

Biological tissue has little inherent contrast in either the light or electron microscope.

histochemistry is used.[9]

Light microscopy

Masson's trichrome staining on rat trachea

acidic dye, stains the cytoplasm and other tissues in different stains of pink.[9][12]

In contrast to H&E, which is used as a general stain, there are many techniques that more selectively stain cells, cellular components, and specific substances.

silver stains) are useful in identifying neurons are other examples of more specific stains.[12]

Historadiography

In

dark field microscopy
.

Immunohistochemistry

Main article: immunohistochemistry

Recently,

Fluorescence microscopy and confocal microscopy
are used to detect fluorescent signals with good intracellular detail.

Electron microscopy

Main article: Electron microscope § Sample preparation

For electron microscopy heavy metals are typically used to stain tissue sections.[9] Uranyl acetate and lead citrate are commonly used to impart contrast to tissue in the electron microscope.[9]

Specialized techniques

Cryosectioning

Main article: Frozen section procedure

Similar to the

tumors to allow rapid identification of tumor margins, as in Mohs surgery
, or determination of tumor malignancy, when a tumor is discovered incidentally during surgery.

Ultramicrotomy

Transmission electron microscope
Main article: Ultramicrotomy

Ultramicrotomy is a method of preparing extremely thin sections for

ultramicrotome.[12]

Artifacts

Artifacts are structures or features in tissue that interfere with normal histological examination. Artifacts interfere with histology by changing the tissues appearance and hiding structures. Tissue processing artifacts can include pigments formed by fixatives,[12] shrinkage, washing out of cellular components, color changes in different tissues types and alterations of the structures in the tissue. An example is mercury pigment left behind after using Zenker's fixative to fix a section.[12] Formalin fixation can also leave a brown to black pigment under acidic conditions.[12]

History

Santiago Ramón y Cajal in his laboratory

In the 17th century the Italian Marcello Malpighi used microscopes to study tiny biological entities; some regard him as the founder of the fields of histology and microscopic pathology.[20][21] Malpighi analyzed several parts of the organs of bats, frogs and other animals under the microscope. While studying the structure of the lung, Malpighi noticed its membranous alveoli and the hair-like connections between veins and arteries, which he named capillaries. His discovery established how the oxygen breathed in enters the blood stream and serves the body.[22]

In the 19th century histology was an academic discipline in its own right. The French anatomist Xavier Bichat introduced the concept of tissue in anatomy in 1801,[23] and the term "histology" (German: Histologie), coined to denote the "study of tissues", first appeared in a book by Karl Meyer in 1819.[24][25][20] Bichat described twenty-one human tissues, which can be subsumed under the four categories currently accepted by histologists.[26] The usage of illustrations in histology, deemed as useless by Bichat, was promoted by Jean Cruveilhier.[27][when?]

In the early 1830s Purkynĕ invented a microtome with high precision.[25]

During the 19th century many

Benedikt Stilling (freezing).[25]

gum Arabic; Salomon Stricker (1834–1898), who advocated a mixture of wax and oil; and Andrew Pritchard (1804–1884) who, in 1832, used a gum/isinglass mixture. In the same year, Canada balsam appeared on the scene, and in 1869 Edwin Klebs (1834–1913) reported that he had for some years embedded his specimens in paraffin.[28]

The 1906

Santiago Ramon y Cajal. They had conflicting interpretations of the neural structure of the brain based on differing interpretations of the same images. Ramón y Cajal won the prize for his correct theory, and Golgi for the silver-staining technique that he invented to make it possible.[29]

Future directions

In vivo histology

There is interest in developing techniques for in vivo histology (predominantly using

MRI), which would enable doctors to non-invasively gather information about healthy and diseased tissues in living patients, rather than from fixed tissue samples.[30][31][32][33]

See also

Notes

  1. combining histo- + -logy to mean "study of tissue"; from the Greek words ἱστός (histós) "tissue", and -λογία (-logía
    ) "study of".

References

  1. ^ "Microanatomy definition and meaning". Collins English Dictionary.
  2. ^ "Histology | physiology". Encyclopedia Britannica. Retrieved 2018-10-29.
  3. ^ "DefinedTerm: Histology". Defined Term. Archived from the original on 2018-10-29. Retrieved 2018-10-29.
  4. ^ Maximow, Alexander A.; Bloom, William (1957). A textbook of Histology (Seventh ed.). Philadelphia: W. B. Saunders Company.
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  12. ^ a b c d e f g h i j k l m n o p q r s t Bancroft, John; Stevens, Alan, eds. (1982). The Theory and Practice of Histological Techniques (2nd ed.). Longman Group Limited.
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  23. ^ Bichat X (1801). "Considérations générales". Anatomie générale appliquée à la physiologie et à la médecine (in French). Paris: Chez Brosson, Gabon et Cie, Libraires, rue Pierre-Sarrazin, no. 7, et place de l'École de Médecine. pp. cvj–cxj.
  24. ^ Mayer AF (1819). Ueber Histologie und eine neue Eintheilung der Gewebe des menschlichen Körpers (in German). Bonn: Adolph Marcus.
  25. ^
    doi:10.13070/rs.en.2.1283 (inactive 1 November 2024). Archived from the original on 13 April 2021. Retrieved 3 May 2018.{{cite journal}}: CS1 maint: DOI inactive as of November 2024 (link
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    . Most of Bichat's twenty-one tissues can be subsumed under the four categories generally accepted by contemporary histologists; epithelium, connective tissue, muscle, and nerve. Four of Bichat's tissues fall under the heading of epithelium (epidermoid, mucous, serous, and synovial); six under connective tissue (dermoid, fibrous, fibrocartilaginous, cartilaginous, osseous, and cellular); two under muscle; and two under nerve — the distinction between nervous governing "animal" life and nervous governing "organic" life corresponds with that between the voluntary and involuntary nervous systems. The arteries and the veins, long sources of contention, are classified today as compound tissues. The absorbents and the exhalants (which Bichat thought to be open-ended vessels) have dropped out or been replaced by the lymphatics. His medullary system has no counterpart among the present-day tissues.
  27. ^ Meli DB (2017). Visualizing disease: the art and history of pathological illustrations. Chicago: The University of Chicago Press.[page needed]
  28. ^ Bock, Ortwin (2015-01-05). "A history of the development of histology up to the end of the nineteenth century". Research. Archived from the original on 2021-04-13. Retrieved 2018-05-03.
  29. ^ "The Nobel Prize in Physiology or Medicine 1906". NobelPrize.org.
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