Histology

A thin section of lung tissue stained with hematoxylin and eosin. This individual suffers from emphysema.

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Histology (from the Greek Template:Polytonic) 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.

## Contents

* 1 Technical Procedure
* 1.1 Fixation
* 1.2 Processing
* 1.3 Embedding
* 1.4 Sectioning
* 1.5 Staining
* 2 Common Laboratory Stains
* 2.1 Alternative techniques
* 3 History
* 4 Histological classification of animal tissues
* 5 Related sciences
* 6 Artifacts
* 6.1 Pre-histology
* 6.2 Post-histology
* 7 References
* 8 See also
* 9 External links

## Technical Procedure[edit | edit source]

### Fixation[edit | edit source]

Main article: Fixation (histology)

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.

### Processing[edit | edit source]

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:

### Embedding[edit | edit source]

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.

### Sectioning[edit | edit source]

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.

### Staining[edit | edit source]

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.

## Common Laboratory Stains[edit | edit source]

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.CS1 maint: Multiple names: authors list (link)

The Nissl method and Golgi's method are useful in identifying neurons.

### Alternative techniques[edit | edit source]

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 epoxy resin. Very thin sections (less than 0.1 micrometers) are cut using diamond or glass knives. The sections are stained with electron dense stains (uranium and lead) so that they can be seen with the electron microscope.

## History[edit | edit source]

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 Santiago Ramon y Cajal. They had dueling interpretations of the neural structure of the brain based in differing interpretations of the same images.

## Histological classification of animal tissues[edit | edit source]

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 cells: 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 cells: reproductive cells, spermatozoa in men, oocytes 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, and
* Stem cells: cells able to turn into one or several of the above types.

Note that tissues from plant, fungus and microorganisms can also be examined histologically. Their structure is very different from animal tissue.

## Related sciences[edit | edit source]

* Cell biology is the study of living cells, their DNA, RNA and the proteins they express.
* Anatomy, is the study of organs visible by the naked eye; and
* Morphology, which studies entire organisms.

## Artifacts[edit | edit source]

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[edit | edit source]

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[edit | edit source]

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.

## References[edit | edit source]

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)

## See also[edit | edit source]

* Pathology
* Anatomical pathology
* Histopathology
* Biological staining
* Important publications in histology
* Geoffrey Bourne

## External links[edit | edit source]

* Histology Protocols
* Immunohistochemistry - In Situ Hybridization
* Histoweb
* SIU SOM Histology
* Visual Histology Atlas
* Histology Glossary
* Histology Group of Victoria Incorporated
* Histology Photomicrographs

* v
* t
* e

Proteins of epithelium

Lateral/cell-cell|

* Cell adhesion molecules: Adherens junction
* Cadherin
* Desmosome
* Desmoglein

* Ion channels: Gap junction/Connexon
* Connexin

* Cytoskeleton: Desmosome
* Desmoplakin
* Plakoglobin
* Tonofibril

* other membrane proteins: Tight junction
* Claudin
* Occludin
* MARVELD2

Basal/cell-matrix|

* Basal lamina
* Hemidesmosome/Tonofibril
* Focal adhesion
* Costamere

Apical|

* Cilia/Kinocilium
* Microvilli/Stereocilia (STRC)

* v
* t
* e

Connective tissues

Physiology|

* Soft tissue
* Fibrosis
* Scarring

Composition|

| Cells|

| Resident|

* Fibroblast
* Fibrocyte
* Reticular cell
* Tendon cell
* Adipocyte
* Melanocyte

|

Wandering cells|

* Mast cell
* Macrophage

Extracellular
matrix|

| Ground substance|

* Tissue fluid

|

Fibers|

* Collagen fibers
* Reticular fibers
* COL3A1
* Elastic fibers
* Elastin
* Fibrillin
* FBN1
* FBN2
* FBN3
* EMILIN1
* Elaunin

Types|

| Proper|

| Loose|

* Reticular
* Adipose
* Brown
* White

|

Dense|

* Dense irregular connective tissue
* Submucosa
* Dermis
* Dense regular connective tissue
* Ligament
* Tendon
* Aponeurosis

Embryonic|

* Mucoid
* Mesenchymal

Specialized|

* Cartilage
* Bone

* v
* t
* e

Muscle tissue

Smooth
muscle|

* Calmodulin
* Vascular smooth muscle

Striated
muscle|

| Skeletal
muscle|

| Costamere/
DAPC|

| Membrane/
extracellular|

| DAP:|

* Sarcoglycan
* SGCA
* SGCB
* SGCD
* SGCE
* SGCG
* SGCZ
* Dystroglycan

|

* Sarcospan
* Laminin, alpha 2

Intracellular|

* Dystrophin
* Dystrobrevin
* A
* B
* Syntrophin
* A
* B1
* B2
* G1
* G2
* Syncoilin
* Dysbindin
* Synemin/desmuslin

related:|

* NOS1
* Caveolin 3

Sarcomere/
(a, i, and h bands;
z and m lines)|

* Myofilament
* thin filament/actin
* thick filament/myosin
* elastic filament/titin
* nebulin

* Tropomyosin

* Troponin
* T
* C
* I

Connective tissue|

* Epimysium
* Fascicle
* Perimysium
* Endomysium
* Connective tissue in skeletal muscle

General|

* Neuromuscular junction
* Motor unit
* Muscle spindle
* Excitation–contraction coupling
* Sliding filament mechanism

Cardiac
muscle|

* Myocardium
* Intercalated disc
* Nebulette

Both|

| Fiber|

* Muscle fiber
* intrafusal
* extrafusal
* Myofibril
* Microfilament/Myofilament
* Sarcomere

|

Cells|

* Myoblast/Myocyte
* Myosatellite cell

Other|

* Desmin
* Sarcoplasm
* Sarcolemma
* T-tubule
* Sarcoplasmic reticulum

Other/
ungrouped|

* Myotilin
* Telethonin
* Dysferlin
* Fukutin
* Fukutin-related protein

* v
* t
* e

Nervous tissue

CNS|

| Tissue Types|

* Grey matter
* White matter
* Projection fibers
* Association fiber
* Commissural fiber
* Lemniscus
* Nerve tract
* Decussation
* Commissure
* Neuropil
* Meninges

|

Cell Types|

| Neuronal|

* Pyramidal
* Purkinje
* Granule
* Spindle
* Interneuron

|

Glial|

| insulating:|

* Myelination: Oligodendrocyte

|

other|

* Astrocyte
* Ependymal cells
* Tanycyte
* Microglia

PNS|

| General|

* Dorsal
* Root
* Ganglion
* Ramus
* Ventral
* Root
* Ramus
* Ramus communicans
* Gray
* White
* Autonomic ganglion (Preganglionic nerve fibers
* Postganglionic nerve fibers)
* Nerve fascicle
* Funiculus

|

Connective tissues|

* Epineurium
* Perineurium
* Endoneurium

Neuroglia|

* Myelination: Schwann cell
* Neurilemma
* Myelin incisure
* Node of Ranvier
* Internodal segment
* Satellite glial cell

Neurons/
nerve fibers|

| Parts|

| Soma|

* Axon hillock

|

Axon|

* Telodendron
* Axon terminals
* Axoplasm
* Axolemma
* Neurofibril/neurofilament

Dendrite|

*     * Nissl body
* Dendritic spine
* Apical dendrite/Basal dendrite

Types|

* Bipolar
* Unipolar
* Pseudounipolar
* Multipolar
* Interneuron
* Renshaw

Afferent nerve fiber/
Sensory neuron|

* GSA
* GVA
* SSA
* SVA
* fibers
* Ia or Aα
* Ib or Golgi or Aα
* II or Aβ and Aγ
* III or Aδ or fast pain
* IV or C or slow pain

Efferent nerve fiber/
Motor neuron|

* GSE
* GVE
* SVE
* Upper motor neuron
* Lower motor neuron
* α motorneuron
* β motorneuron
* γ motorneuron

Termination|

| Synapse|

* Electrical synapse/Gap junction
* Chemical synapse
* Synaptic vesicle
* Active zone
* Postsynaptic density
* Autapse
* Ribbon synapse
* Neuromuscular junction

|

Sensory receptors|

* Meissner's corpuscle
* Merkel nerve ending
* Pacinian corpuscle
* Ruffini ending
* Muscle spindle
* Free nerve ending
* Nociceptor
* Olfactory receptor neuron
* Photoreceptor cell
* Hair cell
* Taste bud

af:Histologie ar:علم الأنسجة an:Istolochía ast:Histoloxía bs:Histologija bg:Хистология ca:Histologia cs:Histologie da:Histologi de:Histologie et:Histoloogia el:Ιστολογία eo:Histologio eu:Histologia fa:بافت‌شناسی gl:Histoloxía hr:Histologija id:Histologi it:Istologia he:היסטולוגיה lb:Histologie lt:Histologija mk:Хистологија ms:Histologi nl:Histologie no:Histologi nn:Histologi simple:Histology sk:Histológia sr:Хистологија sh:Histologija fi:Kudosoppi sv:Histologi th:มิญชวิทยา uk:Гістологія

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