Histology

Histology (from gr histos " tissue" and logos " doctrine "), even histology, is the science of biological tissues. The histology is therefore a branch of medicine or biology and here again the branch of anatomy or pathology.

The histologist examined tissue samples. These micrometer- thin, stained tissue sections are prepared and evaluated under the microscope. One speaks of morphological diagnostics as the basis of the appearance and the dyeing characteristics of tissue structures of the findings will be created. For sample material at the histological work includes surgical specimens (eg, stomach, intestine, kidney ), biopsies (eg, birthmarks, tendons, cysts ) and biopsies (eg, stomach, colon, breast tissue biopsies ). With the help of modern technology can already be on tiny pieces of tissue (1-2 mm) Create histological diagnoses. These micro-invasive methods are gentle on the patient and are often performed at screening.

The electron microscopic examination of tissue also falls primarily within the research area. Here 0.01-0.5 micron thick sections are prepared and examined with a high resolution electron microscope.

The tasks of the histopathology include the early diagnosis of tumors ( eg gastric biopsy), tumor classification ( gut-/bösartig ), detection of metabolic diseases, parasitic, bacterial, inflammatory diseases, assistance for choice of therapy and much more.

History

Henri Louis Duhamel du Monceau noted that animal bones with the dye from the madder Färberkrappflanze ( Rubia tinctorum ) can stain. Even Christian Gottfried Ehrenberg in 1838 Carmine used for staining and microscopic observation of Infusorientierchen (or protists ). Then in 1849 studied Heinrich Ferdinand Julius Cohn Goeppert and by means of dyes madder and carmine the protoplasmic streaming in plant cells. One who further developed the histological staining techniques, was about the year 1855 the anatomist Joseph von Gerlach. He describes the staining of cell nuclei in animal cells by Carmine. Heinrich Wilhelm Waldeyer will use in 1863 by means of an extract of the Bloodwood tree ( Haematoxylum campechianum ) the hematoxylin for nerve cells. Another important step was the use of aniline dyes by Paul Ehrlich; he is perfecting these opportunities in the years 1879-1894.

As the founder of histology to Marie François Xavier Bichat (1771-1802), who described 21 types of tissue in the human body without a microscope. The emergence of the histopathology ascribed to Johannes Peter Müller (1801-1858), who in 1838 published a book on the nature and structure properties of cancer. As a father of histopathology is called Rudolf Virchow ( 1821-1902 ). The term histology was in 1819 by the anatomist Franz Josef Carl Mayer ( 1787-1865 ) defined and considered as a branch of anatomy. In 1830, influenced Vincent Jaques Louis Chevalier ( 1770-1841 ) and his son Charles Louis Chevalier ( 1804-1859 ), whose company produced scientific instruments in Paris since 1765, the term microtome for tissue cutting devices.

Histological technique

Before a pathologist / biologist can examine the histological details of a patient sample / an experiment, the tissue of a detailed processing needs to be undergone. These methods are summarized as histological techniques and are implemented in the histological laboratory mostly from biomedical analysts or (V ) MTAs.

Tissue processing in histodiagnostischen laboratory includes:

• Fixation for stabilization of the tissue ( Hauptfixans: 4 % neutral buffered formaldehyde solution)
• Macroscopic inspection, cutting the meaningful fabric districts. In pathology, medical work and for the diagnostic process belonging.
• Dewatering and impregnation of the tissue with liquid paraffin
• Einblocken the tissue in paraffin: a paraffin cube is prepared which contains the tissue.
• In modern Histologielaboren the Gewebsstückchen be placed in so-called " Embedding ". In these, the tissue sample through the drain and Einparaffinierung. After the cartridge is used as a block pad and can be clamped as in the so-called quick-release frame to which most of today's microtomes are provided.
• Production of 2-5 microns thick sections on the microtome
• Mounting the sections on (coated ) glass slides
• Histological staining techniques

The processing of formaldehyde - fixed, paraffin - embedded tissue, including the hematoxylin- eosin staining represents the global routine method of Pathology and takes an average of one to two days from sample receipt to reporting. In contrast to the clinical chemistry laboratory many steps are carried out by hand. In particular, the section on the microtome production requires great skill.

Frozen section analysis

For some operations, the surgeon needs during surgery information on the removed tissue for its further course of action. In this case, a portion of the sample is used within about 10 minutes as a frozen section:

• Tissue stabilization by freezing ( about -20 ° C), depending on the type of tissue
• Producing a 5-10 microns thick cut with a cryostat microtome
• Raising the cut on a coated glass slide
• Dyeing by means of quick - HE staining, Paragon staining or other quick staining
• Microscopic findings

Staining of histology

There are a myriad of different histological stains that have been developed over the last 120 years. The majority comes from the first 30 years of the last century. In modern Histolabor a manageable number of colorations has prevailed. First, the hematoxylin -eosin staining ( HE staining ) is as routine and Overview staining. For computer-controlled stainer are mostly used. In addition, so-called special stains (mostly by hand) carried out for certain issues.

The Färbetheorie of biological stains usually is due to the reaction capacity of certain tissue structures to certain dyes. It classifies the cell structures and tissue based on the staining behavior of the dyes in basophilic, acidophilic and neutrophilic structures.

• Basophils structures such as the nucleus, ribosomes and rough endoplasmic reticulum, they contain acid groups and therefore are stained with basic dyes on (hematoxylin, hematoxylin, Azokarmin, methylene blue, toluidine blue ). A basic dye is chemically a substance that can release anions or cations absorb. It therefore behaves as a reducing agent, such as an electron donor and is oxidized in a chemical reaction thereby.
• Acidophilic structures are approximately the cytoplasm, collagen fibers, these are basic and therefore are stained with acidic dyes such as eosin, aniline blue, picric acid, acid fuchsin.
• Neutrophils structures of the cell are stained by either basic or acid dyes by. There are mainly lipophilic constituents.
• Argyrophilic structures bind silver ions bind argentaffine structures and reduce silver ions to elemental silver.
• The nucleus can be stained by nucleophilic dyes. Most of them are basic, or DNA-binding dyes that bind to nucleic acids.

Analyzed to the dyeing process histochemically a complicated picture of physico-chemical processes, consisting of physical processes such as diffusion, electroadsorption and Grenzflächenadsorption, from the above described chemical processes with respect to charge distribution in the dye molecule (see also Lewis acid - base concept ) and indicated the histological structures.

The main binding force is the ionic bond (acid dyes are bound to basic proteins ). For histochemical methods, a dye only ( Perjodacid - Schiff reaction eg Prussian blue reaction ) developed by the reaction with a fabric ingredient. Further, there are enzyme-histochemical methods, in which the activity of cellular enzymes causes a color development.

This classic Histology is complemented since the 1980s by immunohistochemistry. Here the detection is based on " cell properties " on an antigen- antibody reaction. In a multi - step technique, the reaction is visualized by a color reaction at the site of the antigen ( protein).

Since the 1990s, the in situ hybridization attention during histological diagnosis. This is based on the detection of specific nucleotide sequences of the double-stranded DNA melting and of spontaneous deposition of individual strands (DNA or RNA). The nucleic acid sequences are represented by means of probes. Are these probes labeled with fluorochromes, it is called fluorescence in situ hybridization ( FISH).

With these methods, a new section of Histodiagnostik has begun.

Conventional staining methods are:

• Azan staining ( Azokarmin G- aniline blue ): Nuclei red, reddish cytoplasm, collagen and reticular fibers blue, red muscle fibers
• Prussian blue reaction: detection of trivalent iron ions in the tissue
• Heidenhain 's iron hematoxylin ( EH )
• Giemsa staining: differentiating blood cells staining
• Golgi staining: silver single neurons with silver nitrate (so-called " black reaction" )
• Gram stain: gram- positive bacteria differentiation (blue) and gram- negative ( red)
• Hematoxylin -eosin staining ( HE): Nuclei, bacteria and lime blue; Cytoplasm reddish / bluish, collagen red
• Congo red staining: Presentation of amyloidosis amyloid deposits
• LFB ( Luxol fast blue / cresyl violet ): myelin sheaths turquoise blue, nuclei blue-violet
• New Metyhlenblau staining, NMB staining
• PAS reaction ( periodic acid - Schiff's reagent): neutral glycoconjugates ( mucilage ) magenta
• Reticulinfärbung by Gomori: silver; reticular fibers black
• Trichrome Masson - Goldner ( Eisenhämatoxilin / acid fuchsin / orange G / light green): differential staining of the connective tissue, cell nuclei blue-black, cytoplasm red, collagen green, light red muscles
• Van Gieson ( hematoxylin / picric acid / acid fuchsin ): cores black - brown, yellow- brown cytoplasm, collagen ( connective tissue) red, orange muscle
• Von Kossa staining: silver; calcifications black
• Ziehl- Neelsen staining: Acid-resistant bacteria (especially tuberculosis bacteria ) red

See also:

• Silver staining

Tissue types

• Connective and supporting tissue connective tissue
• Adipose tissue
• Bone tissue
• Cartilage tissue