The histology (from ancient Greek ἱστός histos , German , tissue ' and -logie , gr. Λόγος logos , teaching') or Histology is the science of the biological tissues . As "the study of the formation and structure of plant and animal tissues in relation to specific functions" it is a branch of medicine and biology . In a broader sense, histology describes the microscopic anatomy . The histopathology is the science of the diseased tissue changes.
Tissue samples are examined in histology. For this purpose, micrometer-thin , colored tissue sections are produced and assessed using a light microscope . The electron microscopic examination of much thinner sections (0.01–0.5 µm) is mainly a research area.
The tissue examinations in medicine serve various purposes: early diagnosis of tumors (e.g. gastric biopsy), classification of tumors (benign / malignant), detection of metabolic diseases and parasitic, bacterial, inflammatory diseases, help in choosing a therapy and much more. One speaks of morphological diagnostics, since the findings are based on the appearance and the coloring behavior of the tissue structures.
Samples for histological work include surgical specimens (e.g. stomach, intestines, kidneys), sample excisions (e.g. birthmarks, tendons, cysts) and biopsies (e.g. stomach, intestinal, breast tissue biopsies). With the help of modern technology, fine-tissue diagnoses can be made on tiny pieces of tissue (1–2 mm). These micro-invasive methods are gentle on the patient and are often carried out during preventive examinations.
Development of dyeing techniques
Marcello Malpighi (1628–1694) was one of the first to examine animal organs and plants under the microscope. Henri Louis Duhamel du Monceau (1700–1782) found that animal bones can be colored with madder from the madder plant (Rubia tinctorum). The development of staining methods was decisive for the further development of histology, since the natural preparations were largely colorless and the optical density of the tissue structures to be examined usually does not differ much. In 1838 Christian Gottfried Ehrenberg used carmine for staining and microscopic observation of protists (who were then called infusoria ). In 1849 Heinrich Göppert and Ferdinand Julius Cohn studied the protoplasmic flow in plant cells using the dyes madder and carmine. Around 1855 the anatomist Joseph von Gerlach further developed the histological staining techniques. He described the staining of cell nuclei in animal cells using carmine.
In 1863 Heinrich Wilhelm Waldeyer used an extract of the bloodwood tree ( Haematoxylum campechianum ) for the hematoxylin staining of nerve cells. Another important step was the use of aniline dyes by Paul Ehrlich ; he perfected these possibilities in the years 1879 to 1894.
Origin of histology
Xavier Bichat (1771–1802) is considered the founder of histology , who described 21 types of tissue in the human body without the microscope, which was already well known in the 17th century. The development of histopathology is attributed to Johannes Müller (1801-1858), who in 1838 published a book on the nature and structural properties of cancer. Rudolf Virchow (1821–1902) is referred to as the father of histopathology .
The term histology was paraphrased in 1819 by the anatomist Franz Josef Carl Mayer (1787–1865) and viewed as a branch of anatomy . In 1830, Vincent Jaques Louis Chevalier (1770–1841) and his son Charles Louis Chevalier (1804–1859) coined the term microtome for tissue cutting devices. Her company had been manufacturing scientific instruments in Paris since 1765.
Slides can be completely digitized in so-called Whole Slide Images (WSI) . These WSIs can then be shared with colleagues, evaluated by algorithms or, for example, hosted on the web for teaching purposes. An example of such a project is Pathorama , preci.cloud or Cytomine.
Before the fine tissue details of a patient sample or an experiment can be examined, the tissue must undergo extensive processing. These methods are summarized as a histological technique and are mostly carried out in the histological laboratory by biomedical analysts or (V) MTAs .
Tissue processing in the histodiagnostic laboratory includes:
- Fixation to stabilize the tissue (main fixant: 4% neutral buffered formaldehyde solution)
- macroscopic assessment, cutting of the meaningful tissue areas. Medical activity in pathology and part of the diagnostic process.
- Drainage and impregnation of the fabric with liquid paraffin
- Blocking the tissue in paraffin: a paraffin block is made that contains the tissue.
- In modern histology laboratories, the pieces of tissue are placed in so-called "embedding cassettes". In these, the tissue sample goes through dehydration and waxing. The cassette then serves as a pad base and can thus be clamped into the so-called quick - release frame with which most microtomes today are fitted.
- Production of 2–5 µm thick sections on the microtome
- Drawing up the sections on (coated) glass slides
- histological staining techniques
The processing of formaldehyde-fixed, paraffin-embedded tissue, including hematoxylin-eosin staining, is the worldwide routine method of pathology and takes an average of one to two days from sample acceptance to diagnosis . In contrast to the clinical-chemical laboratory, many work steps have to be carried out by hand. Creating sections on the microtome in particular requires great skill.
Rapid section examination
In some operations, the surgeon needs information about the removed tissue during the operation so that he can proceed further. In this case, part of the sample can be processed as a quick section within about ten minutes:
- Tissue stabilization by freezing (approx. −20 ° C), depending on the type of tissue
- Prepare a 5–10 µm thick section with a cryostat microtome
- Drawing up the section on a coated glass slide
- Staining by means of rapid HE staining, Paragon staining or another rapid staining
- microscopic diagnosis
Staining methods of histology
There are a myriad of different histological stains that have been developed over the past 120 years. Most of it comes from the first 30 years of the last century. A manageable number of stains has established itself in the modern histological laboratory. The hematoxylin-eosin stain (HE stain) comes first as routine and overview staining. Computer-controlled staining machines are mostly used for this. In addition, so-called special staining (mostly by hand) is carried out for certain questions .
The staining theory of biological staining is mostly based on the ability of certain tissue structures to react to certain dyes. The cell structures and tissues are classified into basophilic , acidophilic and neutrophilic structures based on the coloring behavior of the dyes .
- Basophilic structures are the cell nucleus , the ribosomes and the rough endoplasmic reticulum ; they contain acid groups and are therefore stained with basic dyes ( hematoxylin , iron hematoxylin, azo carmine , methylene blue , toluidine blue ). From a chemical point of view, a basic dye is a substance that can split off anions or take up cations .
- Acidophilic structures are the cytoplasm , collagen fibers. These are basic and are therefore colored with acidic dyes such as eosin , aniline blue , picric acid and acid fuchsin .
- Neutrophil structures of the cell are not stained by either basic or acidic dyes. They are mainly lipophilic components.
- Argyrophilic structures bind silver ions, argent-affine structures bind and reduce silver ions to elemental silver.
- The nucleus can be stained with nucleophilic dyes. Mostly it is basic or DNA-binding dyes that bind to nucleic acids.
If the staining process was analyzed histochemically, a complex picture of physical-chemical processes emerged, consisting of physical processes such as diffusion , electroadsorption and interfacial adsorption , the chemical processes described above with regard to charge distributions in the dye molecule (see also Lewis acid-base concept ) and on the histological structures.
The main binding force is the ionic bond (acidic dyes are bound to basic proteins). In histochemical methods, a dye only develops through the reaction with a tissue component (e.g. Prussian blue reaction, periodic acid-Schiff reaction). There are also enzyme histochemical methods in which the activity of the cell's own enzymes causes color to develop .
This classic histochemistry has been supplemented by immunohistochemistry since the 1980s . Here, the detection of “cell properties” is based on an antigen-antibody reaction . In a multi-step technique, the reaction becomes visible through a color reaction at the location of the antigen (protein).
In-situ hybridization has been used in histological diagnostics since the 1990s . Here, the detection of certain nucleotide sequences is based on the melting of double-stranded DNA and the spontaneous attachment of single strands (DNA or RNA ). The nucleic acid sequences are displayed using probes . If these probes are marked with fluorochromes , one speaks of fluorescence in situ hybridization (FISH) .
With these methods a new section of histodiagnostics has begun.
Common staining methods are:
- Alcian blue staining : acidic polysaccharides and proteoglycans cyan
- Azan staining ( azo carmine G - aniline blue ): cell nuclei red, cytoplasm reddish, collagen and reticular fibers blue, muscle fibers red
- Prussian blue reaction : detection of trivalent iron ions in the tissue
- Dorner-Snyder stain : endospores
- Iron hematoxylin according to Heidenhain (EH)
- Elastica staining (Weigert staining, with resorcinol fuchsin / orcein): elastic fibers black-violet
- Giemsa stain : differentiating blood cell staining
- Gimenez stain : bacteria, especially rickettsiae, legionella, bartonella, coxiella
- Golgi color : silvering of individual neurons with silver nitrate (so-called "black reaction")
- Gram staining : bacterial differentiation into gram-positive (blue) and gram-negative (red)
- Hematoxylin-eosin stain (HE): cell nuclei, bacteria and calcium blue; Cytoplasm reddish / bluish, collagen red
- Congo red staining: representation of amyloid deposits amyloidosis
- LFB (Luxol Fast Blue / Cresyl violet): medullary sheaths turquoise blue, nuclei blue-violet
- May-Grünwald staining : cell nuclei, differentiating blood cell staining
- Moeller staining : endospores
- Neu-methylene blue staining, NMB staining
- Pappenheim staining : cell nuclei, differentiating blood cell staining
- PAS reaction : (periodic acid- Schiff's reagent ): neutral glycoconjugates (mucilage) magenta red
- Picro Sirius red stain : collagen
- Reticulin staining according to Gömöri: silver staining , reticular fibers black
- Schaeffer-Fulton staining : endospores
- Toluidine blue stains acidic molecules
- Trichrome stains , e.g. B. According to Masson-Goldner (iron hematoxylin / acid fuchsin / orange G / light green): differentiated staining of the connective tissue components, cell nuclei blue-black, cytoplasm red, collagen green, muscles light red
- Van Gieson staining (iron hematoxylin / picric acid / acid fuchsin): nuclei brown-black, cytoplasm yellow-brown, collagen (connective tissue) red, muscles orange
- Vanillin-HCl coloring colors tannins
- von Kossa coloring : silver coloring , calcifications black
- Wright staining : cell nuclei, differentiating blood cell staining
- Ziehl-Neelsen staining and Kinyoun staining : acid-fast bacteria (especially tuberculosis bacteria ) red
- Endospore staining
- Connective and supporting tissue
- Epithelial tissue
- Muscle tissue
- Nerve tissue
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- Centralize your research workflow | PreciCloud. Retrieved September 6, 2018 .