Misplaced Pages

#82917

64-402: There are four basic types of animal tissues: muscle tissue , nervous tissue , connective tissue , and epithelial tissue . 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 ). For plants, the study of their tissues falls under

128-409: A tear gas agent. Oxidation and ammoxidation also target the methyl groups, affording dicarboxylic acids and the dinitriles. Electrophiles attack the aromatic ring, leading to chloro- and nitroxylenes. Xylene is flammable but of modest acute toxicity, with LD 50 ranges from 200 to 5000 mg/kg for animals. Oral LD 50 for rats is 4300 mg/kg. The principal mechanism of detoxification

192-414: A harder medium both as a support and to allow the cutting of thin tissue slices. 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. For light microscopy, paraffin wax is the most frequently used embedding material. Paraffin is immiscible with water,

256-557: A knife mounted in a microtome is used to cut tissue sections (typically between 5-15 micrometers thick) which are mounted on a glass microscope slide . For transmission electron microscopy (TEM), a diamond or glass knife mounted in an ultramicrotome is used to cut between 50 and 150 nanometer thick tissue sections. 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

320-420: A material used for endodontics (root-canal treatments). In the petroleum industry, xylene is also a frequent component of paraffin solvents, used when the tubing becomes clogged with paraffin wax. Xylene is used in the laboratory to make baths with dry ice to cool reaction vessels, and as a solvent to remove synthetic immersion oil from the microscope objective in light microscopy . In histology , xylene

384-648: A microscope. Other advanced techniques, such as nonradioactive in situ hybridization, can be combined with immunochemistry 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. For electron microscopy heavy metals are typically used to stain tissue sections. Uranyl acetate and lead citrate are commonly used to impart contrast to tissue in

448-451: A mixture of the xylenes plus ethylbenzene . The four compounds have identical molecular formulas C 8 H 10 . Typically the four compounds are produced together by various catalytic reforming and pyrolysis methods. Xylenes are an important petrochemical produced by catalytic reforming and also by coal carbonisation in the manufacture of coke fuel . They also occur in crude oil in concentrations of about 0.5–1%, depending on

512-549: 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. The 1906 Nobel Prize in Physiology or Medicine was awarded to histologists Camillo Golgi and Santiago Ramon y Cajal . They had conflicting interpretations of

576-581: A rhythmic fashion for the whole life of the organism. Hence it has special features. There are three types of muscle tissue in invertebrates that are based on their pattern of striation : transversely striated, obliquely striated, and smooth muscle. In arthropods there is no smooth muscle. The transversely striated type is the most similar to the skeletal muscle in vertebrates. Xylene In organic chemistry , xylene or xylol (from Greek ξύλον (xylon)  'wood'; IUPAC name : dimethylbenzene ) are any of three organic compounds with

640-462: A solvent in printing , rubber , and leather industries. It is a common component of ink, rubber , and adhesives . In thinning paints and varnishes , it can be substituted for toluene where slower drying is desired, and thus is used by conservators of art objects in solubility testing. Similarly it is a cleaning agent , e.g., for steel , silicon wafers , and integrated circuits . In dentistry, xylene can be used to dissolve gutta percha ,

704-463: A specific chemical is the Perls' Prussian blue reaction, used to demonstrate iron deposits in diseases like hemochromatosis . The Nissl method for Nissl substance and Golgi's method (and related silver stains ) are useful in identifying neurons are other examples of more specific stains. In historadiography , a slide (sometimes stained histochemically) is X-rayed. More commonly, autoradiography

SECTION 10

#1732783448083

768-405: A variety of alcohols. The azeotrope with water consists of 60% xylenes and boils at 94.5 °C. As with many alkylbenzene compounds, xylenes form complexes with various halocarbons . The complexes of different isomers often have dramatically different properties from each other. p -Xylene is the principal precursor to terephthalic acid and dimethyl terephthalate , both monomers used in

832-414: Is miscible with the wax, finally melted paraffin wax is added to replace the xylene and infiltrate the tissue. In most histology, or histopathology laboratories the dehydration, clearing, and wax infiltration are carried out in tissue processors which automate this process. Once infiltrated in paraffin, tissues are oriented in molds which are filled with wax; once positioned, the wax is cooled, solidifying

896-491: Is a soft tissue , one of the four basic types of animal tissue . Muscle tissue gives skeletal muscles the ability to contract . Muscle is formed during embryonic development , in a process known as myogenesis . Muscle tissue contains special contractile proteins called actin and myosin which interact to cause movement. Among many other muscle proteins, present are two regulatory proteins , troponin and tropomyosin . Muscle tissue varies with function and location in

960-523: Is about 1.06 kg/liter. This can be contrasted with the density of adipose tissue (fat), which is 0.9196 kg/liter. This makes muscle tissue approximately 15% denser than fat tissue. Skeletal muscle is a highly oxygen-consuming tissue, and oxidative DNA damage that is induced by reactive oxygen species tends to accumulate with age . The oxidative DNA damage 8-OHdG accumulates in heart and skeletal muscle of both mouse and rat with age. Also, DNA double-strand breaks accumulate with age in

1024-436: Is arranged in regular, parallel bundles of myofibrils , which contain many contractile units known as sarcomeres , which give the tissue its striated (striped) appearance. Skeletal muscle is voluntary muscle, anchored by tendons or sometimes by aponeuroses to bones , and is used to effect skeletal movement such as locomotion and to maintain posture . Postural control is generally maintained as an unconscious reflex, but

1088-521: Is converted to isophthalic acid derivatives, which are components of alkyd resins . Generally, two kinds of reactions occur with xylenes: those involving the methyl groups and those involving the ring C–H bonds. Being benzylic and hence weakened, the C–H bonds of the methyl groups are susceptible to free-radical reactions, including halogenation to the corresponding xylene dichlorides (bis(chloromethyl)benzenes), while mono-bromination yields xylyl bromide ,

1152-456: Is divided along the embryo 's length into somites , corresponding to the segmentation of the body (most obviously seen in the vertebral column . Each somite has three divisions, sclerotome (which forms vertebrae ), dermatome (which forms skin), and myotome (which forms muscle). The myotome is divided into two sections, the epimere and hypomere, which form epaxial and hypaxial muscles , respectively. The only epaxial muscles in humans are

1216-408: Is found within the walls of blood vessels (such smooth muscle specifically being termed vascular smooth muscle ) such as in the tunica media layer of the large ( aorta ) and small arteries , arterioles and veins . Smooth muscle is also found in lymphatic vessels, the urinary bladder , uterus (termed uterine smooth muscle ), male and female reproductive tracts , the gastrointestinal tract ,

1280-403: Is involuntary, striated muscle that is found in the walls and the histological foundation of the heart , specifically the myocardium. The cardiac muscle cells , (also called cardiomyocytes or myocardiocytes), predominantly contain only one nucleus, although populations with two to four nuclei do exist. The myocardium is the muscle tissue of the heart and forms a thick middle layer between

1344-411: Is known for its production of products related to light microscopy in the context of research and clinical studies. Biological tissue has little inherent contrast in either the light or electron microscope. Staining is employed to give both contrast to the tissue as well as highlighting particular features of interest. When the stain is used to target a specific chemical component of the tissue (and not

SECTION 20

#1732783448083

1408-409: Is no smooth muscle. The transversely striated type is the most similar to the skeletal muscle in vertebrates. Vertebrate skeletal muscle tissue is an elongated, striated muscle tissue, with the fibres ranging from 3-8 micrometers in width and from 18 to 200 micrometers in breadth. In the uterine wall, during pregnancy, they enlarge in length from 70 to 500 micrometers. Skeletal striated muscle tissue

1472-454: Is non-striated and involuntary. Smooth muscle is found within the walls of organs and structures such as the esophagus , stomach , intestines , bronchi , uterus , urethra , bladder , blood vessels , and the arrector pili in the skin that control the erection of body hair. Skeletal muscle is broadly classified into two fiber types: type I (slow-twitch) and type II (fast-twitch). The density of mammalian skeletal muscle tissue

1536-927: Is oxidation to methylbenzoic acid and hydroxylation to hydroxylene. The main effect of inhaling xylene vapor is depression of the central nervous system (CNS), with symptoms such as headache, dizziness, nausea and vomiting. At an exposure of 100 ppm, one may experience nausea or a headache. At an exposure between 200 and 500 ppm, symptoms can include feeling "high", dizziness, weakness, irritability, vomiting, and slowed reaction time. The side effects of exposure to low concentrations of xylene ( < 200 ppm ) are reversible and do not cause permanent damage. Long-term exposure may lead to headaches, irritability, depression, insomnia, agitation, extreme tiredness, tremors, hearing loss, impaired concentration and short-term memory loss. A condition called chronic solvent-induced encephalopathy , commonly known as "organic-solvent syndrome" has been associated with xylene exposure. There

1600-478: Is possible using appropriate protocols. 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. Tissues are embedded in

1664-830: Is required for certain procedures such as antibody-linked immunofluorescence staining. Frozen sections are often prepared during surgical removal of 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 is a method of preparing extremely thin sections for transmission electron microscope (TEM) analysis. Tissues are commonly embedded in epoxy or other plastic resin. Very thin sections (less than 0.1 micrometer in thickness) are cut using diamond or glass knives on an ultramicrotome . Artifacts are structures or features in tissue that interfere with normal histological examination. Artifacts interfere with histology by changing

1728-407: Is the most widely used clearing agent. Xylene is used to remove paraffin from dried microscope slides prior to staining. After staining, microscope slides are put in xylene prior to mounting with a coverslip. In one large-scale application, para-xylene is converted to terephthalic acid . The major application of ortho-xylene is as a precursor to phthalate esters , used as plasticizer . Meta-xylene

1792-422: Is used in visualizing 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

1856-458: Is very little information available that isolates xylene from other solvent exposures in the examination of these effects. Hearing disorders have been also linked to xylene exposure, both from studies with experimental animals, as well as clinical studies. Xylene is also a skin irritant and strips the skin of its oils, making it more permeable to other chemicals. The use of impervious gloves and masks, along with respirators where appropriate,

1920-399: The erector spinae and small intervertebral muscles, and are innervated by the dorsal rami of the spinal nerves . All other muscles, including those of the limbs are hypaxial, and innervated by the ventral rami of the spinal nerves. During development, myoblasts (muscle progenitor cells) either remain in the somite to form muscles associated with the vertebral column or migrate out into

1984-440: The neurotransmitter acetylcholine . Smooth muscle is found in almost all organ systems such as hollow organs including the stomach , and bladder ; in tubular structures such as blood and lymph vessels , and bile ducts ; in sphincters such as in the uterus, and the eye. In addition, it plays an important role in the ducts of exocrine glands. It fulfills various tasks such as sealing orifices (e.g. pylorus, uterine os) or

Histology - Misplaced Pages Continue

2048-434: The respiratory tract , the arrector pili of skin , the ciliary muscle , and the iris of the eye . The structure and function is basically the same in smooth muscle cells in different organs, but the inducing stimuli differ substantially, in order to perform individual actions in the body at individual times. In addition, the glomeruli of the kidneys contain smooth muscle-like cells called mesangial cells . Cardiac muscle

2112-563: 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. 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

2176-596: The appearance of the flexed biceps resembles the back of a mouse. The same phenomenon occurred in Greek , in which μῦς, mȳs , means both "mouse" and "muscle". There are three types of muscle tissue in vertebrates: skeletal , cardiac , and smooth . Skeletal and cardiac muscle are types of striated muscle tissue . Smooth muscle is non-striated. There are three types of muscle tissue in invertebrates that are based on their pattern of striation: transversely striated, obliquely striated, and smooth muscle. In arthropods there

2240-526: The block and tissue. Paraffin wax does not always provide a sufficiently hard matrix for cutting very thin sections (which are especially important for electron microscopy). Paraffin wax may also be too soft in relation to the tissue, the heat of the melted wax may alter the tissue in undesirable ways, or the dehydrating or clearing chemicals may harm the tissue. Alternatives to paraffin wax include, epoxy , acrylic , agar , gelatin , celloidin , and other types of waxes. In electron microscopy epoxy resins are

2304-469: The body to form all other muscles. Myoblast migration is preceded by the formation of connective tissue frameworks, usually formed from the somatic lateral plate mesoderm . Myoblasts follow chemical signals to the appropriate locations, where they fuse into elongate skeletal muscle cells. The primary function of muscle tissue is contraction . The three types of muscle tissue (skeletal, cardiac and smooth) have significant differences. However, all three use

2368-402: The body. In vertebrates , the three types are: Skeletal muscle tissue consists of elongated, multinucleate muscle cells called muscle fibers , and is responsible for movements of the body. Other tissues in skeletal muscle include tendons and perimysium . Smooth and cardiac muscle contract involuntarily, without conscious intervention. These muscle types may be activated both through

2432-424: The case of glutaraldehyde. This process, while preserving the structural integrity of the cells and tissue can damage the biological functionality of proteins, particularly 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

2496-564: The contraction has occurred. The different muscle types vary in their response to neurotransmitters and hormones such as acetylcholine , noradrenaline , adrenaline , and nitric oxide depending on muscle type and the exact location of the muscle. Sub-categorization of muscle tissue is also possible, depending on among other things the content of myoglobin , mitochondria , and myosin ATPase etc. The word muscle comes from Latin musculus , diminutive of mus meaning mouse , because

2560-493: The electron microscope. Similar to the frozen section procedure employed in medicine, cryosectioning is a method to rapidly freeze, cut, and mount sections of tissue for histology. The tissue is usually sectioned on a cryostat or freezing microtome. The frozen sections are mounted on a glass slide and may be stained to enhance the contrast between different tissues. Unfixed frozen sections can be used for studies requiring enzyme localization in tissues and cells. Tissue fixation

2624-407: The exposure film. Individual silver grains in the film are visualized with dark field microscopy . Recently, antibodies have been used to specifically visualize proteins, carbohydrates, and lipids. This process 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

Histology - Misplaced Pages Continue

2688-576: The field of plant anatomy , with the following four main types: Histopathology is the branch of histology that includes the microscopic identification and study of diseased tissue. It is an important part of anatomical pathology and surgical pathology , as accurate diagnosis of cancer and other diseases often requires histopathological examination of tissue samples. Trained physicians, frequently licensed pathologists , perform histopathological examination and provide diagnostic information based on their observations. The field of histology that includes

2752-418: The formula (CH 3 ) 2 C 6 H 4 . They are derived from the substitution of two hydrogen atoms with methyl groups in a benzene ring; which hydrogens are substituted determines which of three structural isomers results. It is a colorless, flammable, slightly greasy liquid of great industrial value. The mixture is referred to as both xylene and, more precisely, xylenes. Mixed xylenes refers to

2816-647: The four categories currently accepted by histologists. The usage of illustrations in histology, deemed as useless by Bichat, was promoted by Jean Cruveilhier . In the early 1830s Purkynĕ invented a microtome with high precision. During the 19th century many fixation techniques were developed by Adolph Hannover (solutions of chromates and chromic acid ), Franz Schulze and Max Schultze ( osmic acid ), Alexander Butlerov ( formaldehyde ) and Benedikt Stilling ( freezing ). Mounting techniques were developed by Rudolf Heidenhain (1824–1898), who introduced gum Arabic ; Salomon Stricker (1834–1898), who advocated

2880-561: The general structure), the term histochemistry is used. Hematoxylin and eosin ( H&E stain ) is one of the most commonly used stains in histology to show the general structure of the tissue. Hematoxylin stains cell nuclei blue; eosin, an acidic dye, stains the cytoplasm and other tissues in different stains of pink. 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. A commonly performed histochemical technique that targets

2944-489: The highly valued p -xylene via the patented UOP- Isomar process or by transalkylation of xylene with itself or trimethylbenzene. These conversions are catalyzed by zeolites . ZSM-5 is used to facilitate some isomerization reactions leading to mass production of modern plastics. The physical properties of the isomers of xylene differ slightly. The melting point ranges from −47.87 °C (−54.17 °F) ( m -xylene) to 13.26 °C (55.87 °F) ( p -xylene)—as usual,

3008-449: The interaction of the central nervous system as well as by receiving innervation from peripheral plexus or endocrine (hormonal) activation. Striated or skeletal muscle only contracts voluntarily, upon the influence of the central nervous system. Reflexes are a form of non-conscious activation of skeletal muscles, but nonetheless arise through activation of the central nervous system, albeit not engaging cortical structures until after

3072-407: The main constituent of biological tissue, so it must first be removed in a series of dehydration steps. Samples are transferred through a series of progressively more concentrated ethanol baths, up to 100% ethanol to remove remaining traces of water. Dehydration is followed by a clearing agent (typically xylene although other environmental safe substitutes are in use) which removes the alcohol and

3136-439: The most commonly employed embedding media, 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. For light microscopy,

3200-412: The most commonly used fixative is glutaraldehyde , usually as a 2.5% solution in phosphate buffered saline . Other fixatives used for electron microscopy are osmium tetroxide or uranyl acetate . The main action of these aldehyde fixatives is to cross-link amino groups in proteins through the formation of methylene bridges (-CH 2 -), in the case of formaldehyde, or by C 5 H 10 cross-links in

3264-430: The movement of actin against myosin to create contraction. In skeletal muscle, contraction is stimulated by electrical impulses transmitted by the motor nerves . Cardiac and smooth muscle contractions are stimulated by internal pacemaker cells which regularly contract, and propagate contractions to other muscle cells they are in contact with. All skeletal muscle and many smooth muscle contractions are facilitated by

SECTION 50

#1732783448083

3328-516: 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. 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. Muscle tissue Muscle

3392-660: The outer epicardium layer and the inner endocardium layer. Coordinated contractions of cardiac muscle cells in the heart propel blood out of the atria and ventricles to the blood vessels of the left/body/systemic and right/lungs/pulmonary circulatory systems . This complex mechanism illustrates systole of the heart. Cardiac muscle cells, unlike most other tissues in the body, rely on an available blood and electrical supply to deliver oxygen and nutrients and to remove waste products such as carbon dioxide . The coronary arteries help fulfill this function. All muscles are derived from paraxial mesoderm . The paraxial mesoderm

3456-451: The oxygen breathed in enters the blood stream and serves the body. 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, and the term "histology" ( German : Histologie ), coined to denote the "study of tissues", first appeared in a book by Karl Meyer in 1819. Bichat described twenty-one human tissues, which can be subsumed under

3520-906: The para isomer's melting point is much higher because it packs more readily in the crystal structure. The boiling point for each isomer is around 140 °C (284 °F). The density of each isomer is around 0.87 g/mL (7.3 lb/US gal; 8.7 lb/imp gal) and thus is less dense than water . The odor of xylene is detectable at concentrations as low as 0.08 to 3.7 ppm (parts of xylene per million parts of air) and can be tasted in water at 0.53 to 1.8 ppm. P210 , P233 , P240 , P241 , P242 , P243 , P261 , P264 , P271 , P273 , P280 , P301+P310 , P302+P352 , P303+P361+P353 , P304+P312 , P304+P340 , P305+P351+P338 , P312 , P321 , P322 , P331 , P332+P313 , P337+P313 , P362 , P363 , P370+P378 , P403+P233 , P403+P235 , P405 , P501 Xylenes form azeotropes with water and

3584-439: 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, histology technicians and technologists, medical laboratory technicians , and biomedical scientists . Most histological samples need preparation before microscopic observation; these methods depend on

3648-431: The production of polyethylene terephthalate (PET) plastic bottles and polyester clothing. 98% of p -xylene production, and half of all xylenes produced is consumed in this manner. o -Xylene is an important precursor to phthalic anhydride . The demand for isophthalic acid is relatively modest, so m -xylene is rarely sought (and hence the utility of its conversion to the o - and p -isomers). Xylenes are used as

3712-640: The responsible muscles can also react to conscious control. The body mass of an average adult man is made up of 42% of skeletal muscle, and an average adult woman is made up of 36%. Cardiac muscle tissue is found only in the walls of the heart as myocardium , and it is an involuntary muscle controlled by the autonomic nervous system . Cardiac muscle tissue is striated like skeletal muscle, containing sarcomeres in highly regular arrangements of bundles. While skeletal muscles are arranged in regular, parallel bundles, cardiac muscle connects at branching, irregular angles known as intercalated discs . Smooth muscle tissue

3776-524: The skeletal muscle of mice. Smooth muscle is involuntary and non-striated. It is divided into two subgroups: the single-unit (unitary) and multiunit smooth muscle . Within single-unit cells, the whole bundle or sheet contracts as a syncytium (i.e. a multinucleate mass of cytoplasm that is not separated into cells). Multiunit smooth muscle tissues innervate individual cells; as such, they allow for fine control and gradual responses, much like motor unit recruitment in skeletal muscle. Smooth muscle

3840-510: The source. Small quantities occur in gasoline and aircraft fuels . Xylenes are produced mainly as part of the BTX aromatics ( benzene , toluene , and xylenes) extracted from the product of catalytic reforming known as reformate . Several million tons are produced annually. In 2011, a global consortium began construction of one of the world's largest xylene plants in Singapore . Xylene

3904-519: The specimen and method of observation. Chemical fixatives are used to preserve and maintain the structure of tissues and cells; fixation also hardens tissues which aids in cutting the thin sections of tissue needed for observation under the microscope. Fixatives generally preserve tissues (and cells) by irreversibly cross-linking proteins. The most widely used fixative for light microscopy is 10% neutral buffered formalin , or NBF (4% formaldehyde in phosphate buffered saline ). For electron microscopy,

SECTION 60

#1732783448083

3968-433: The tissues appearance and hiding structures. Tissue processing artifacts can include pigments formed by fixatives, 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. Formalin fixation can also leave a brown to black pigment under acidic conditions. In

4032-426: The transport of the chyme through wavelike contractions of the intestinal tube. Smooth muscle cells contract more slowly than skeletal muscle cells, but they are stronger, more sustained and require less energy. Smooth muscle is also involuntary, unlike skeletal muscle, which requires a stimulus. Cardiac muscle is the muscle of the heart. It is self-contracting, autonomically regulated and must continue to contract in

4096-484: Was first isolated and named in 1850 by the French chemist Auguste Cahours (1813–1891), having been discovered as a constituent of wood tar . Xylenes are produced by the methylation of toluene and benzene . Commercial or laboratory-grade xylene produced usually contains about 40–65% of m -xylene and up to 20% each of o -xylene , p -xylene and ethylbenzene . The ratio of isomers can be shifted to favor

#82917