Full Answer
What are artefact pigments?
Artefact pigments Most commonly as a result of fixation Normally lie on top of tissues and not within cells Formalin Mercury Chrome Picrates Formalin pigment Result of fixation of tissue in acid formalin Also called acid haematin Resistant to strong acids Usually associated with blood - containing tissues
What is the treatment for formalin pigment in mitochondria?
Post fixation with dichromate has been recommended for mitochondria. Formalin pigment is a brown/black pigment formed in tissues fixed with acidic formalin. Eliminated by treatment with phenolic formalin.
What is formalin pigment made of?
Formalin Pigment Acid Formaldehyde Hematin Formalin pigment is a brown, granular, doubly refractile deposit seen both intracellularly and extracellularly in tissues which have been fixed with a simple formalin solution, such as formal-saline.
What is fixation in psychology?
Verywell / Cindy Chung. In general, a fixation is an obsessive drive that may or may not be acted on involving an object, concept, or person. Initially introduced by Sigmund Freud, a fixation is a persistent focus of the id’s pleasure-seeking energies at an early stage of psychosexual development. Oral, anal, and phallic fixations occur ...
What is fixation in staining?
DEFINITION OF FIXATION AND STAINING Fixation may be defined as the selective preservation of cell or tissue structures and components for subsequent study. Fixation is selective in the sense that those methods are selected which are most suitable for the particular purpose of the research study.
What does fixation mean in microscopy?
Fixation of tissues is the most crucial step in the preparation of tissue for observation in the transmission electron microscope. Fixation consists of two steps: cessation of normal life functions in the tissue (killing) and stabilization of the structure of the tissue (preservation).
What is fixation and explain?
Definition of fixation : the act, process, or result of fixing, fixating, or becoming fixated: such as. a : a persistent concentration of libidinal energies upon objects characteristic of psychosexual stages of development preceding the genital stage. b : stereotyped behavior (as in response to frustration)
What is the purpose of fixation?
Fixation - types of fixatives. The purpose of fixation is to preserve tissues permanently in as life-like a state as possible. Fixation should be carried out as soon as possible after removal of the tissues (in the case of surgical pathology) or soon after death (with autopsy) to prevent autolysis.
What is the purpose of fixation in microbiology?
The main objectives of fixation were to inhibit cellular autolysis, to preserve cellular components and morphology, and to present cells with a distinct microscopical appearance (Paavilainen et al. 2010). Fixation methods can be divided into two groups: additive and denaturing fixations (St-Laurent et al.
What does fixation mean in biology?
In the fields of histology, pathology, and cell biology, fixation is the preservation of biological tissues from decay due to autolysis or putrefaction. It terminates any ongoing biochemical reactions and may also increase the treated tissues' mechanical strength or stability.
What is fixation example?
The definition of a fixation is a point of focus, an obsession or the chemical reduction into a solid form. An example of a fixation is a compulsion to bite one's nails. noun. 4. An obsessive preoccupation.
What are the two types of fixation?
The two main mechanisms of chemical fixation are cross-linking and coagulation. Cross-linking involves covalent bond formation both within proteins and between them, which causes tissue to stiffen and therefore resist degradation.
What are the types of fixatives?
Popular fixative solutionsPhosphate buffered formalin.Formal calcium.Formal saline.Zinc formalin (unbuffered)Zenker's fixative.Helly's fixative.B-5 fixative.Bouin's solution.More items...
What are the method of fixation?
Types of fixation Fixation of tissues can be achieved by chemical or physical means. Physical methods include heating, micro-waving and cryo-preservation (freeze drying). Heat fixation is rarely used on tissue specimens, its application being confined to smears of micro organisms.
What is chemical fixation?
Chemical fixation is a technique to fix a specimen with chemicals to prevent autolysis by the action of enzymes and deformation of morphologies during specimen preparation. Biological tissues start autolysis caused by their enzymes immediately after stopping the activities of them.
What is the difference between fixative and fixation?
Fixation is considered as physiochemical process where cells or tissues are fixed chemically. Fixatives perform various functions such as prevention of autolysis and tissue putrefaction. Various fixative agents include formaldehyde, glutaraldehyde, osmium tetroxide, glyoxal, picric acid, and so on.
What is used for fixation in electron microscope?
There are several chemicals that are widely used for the initial or primary fixation, including glutaraldehyde, formaldehyde, and acrolein. Glutaraldehyde and acrolein cause extensive, rapid and permanent cross-linking of proteins.
What is fixation example?
The definition of a fixation is a point of focus, an obsession or the chemical reduction into a solid form. An example of a fixation is a compulsion to bite one's nails.
What fixative is used for light microscopy?
formaldehydeSince Blum discovered its hardening properties in 1893, formaldehyde has become the most widely used fixative in the world for specimens to be examined by light microscopy.
What fixative is used for electron microscopy?
Glutaraldehyde is one of the most frequently used fixatives. It reacts rapidly with proteins and because it is a dialdehyde, it stabilizes structures by cross-linking before there is any opportunity for extraction by the buffer.
Fixatives
Chemical or Physical Agents which are used to prevent and preserve the tissue are called fixatives.
Ideal Fixative
It should preserve the tissue volume so that tissue should not change its shape and size.
3. Penetration of fixative
Penetration of tissues depends upon the diffusibility of each individual fixative which is a constant.
Duration of fixation
This depends on the type of fixative e.g. in formaldehyde, duration period is very short otherwise, shrinkage and hardness of tissue will take place.
7. Substances added to vehicles
Different substances are added in a fixative to enhance their function e.g. sodium sulphate and NaCl included in a fixative having mercuric chloride.
Secondary fixation
Secondary fixation of tissue section is done with iodine soln. to remove black crystals.
Fixation Artefacts
Formalin pigment is a brown/black pigment formed in tissues fixed with acidic formalin.
Why should fixatives be made up of stock solutions?
Poor quality reagents can produce poor quality fixation. Some formulated fixatives should be made up from stock solutions immediately before use because they are unstable (eg. Helly’s fluid).
When the temperature of a fixative is raised or lowered (as is sometimes recommended for particular histochemical?
When the temperature of a fixative is raised or lowered (as is sometimes recommended for particular histochemical procedures), the rate of diffusion into the specimen is affected, as is the rate of the chemical
What temperature do you fix a tissue?
For light microscopy initial fixation is usually carried out at room temperature and this may be followed by further fixation at temperatures up to 45°C during tissue processing. This is really a compromise that appears to be widely accepted to produce good quality morphological preservation. Microwave fixation may involve the use of higher temperatures, up to 65°C, but for relatively short periods. See Part 5 for further discussion.
What Is a Fixation?
In general, a fixation is an obsessive drive that may or may not be acted on involving an object, concept, or person. Initially introduced by Sigmund Freud, a fixation is a persistent focus of the id’s pleasure-seeking energies at an early stage of psychosexual development. Oral, anal, and phallic fixations occur when an issue or conflict in a psychosexual stage remains unresolved, leaving the individual focused on this stage and unable to move onto the next.
What is fixation in psychology?
In general, a fixation is an obsessive drive that may or may not be acted on involving an object, concept, or person. Initially introduced by Sigmund Freud, a fixation is a persistent focus of the id’s pleasure-seeking energies at an early stage of psychosexual development. Oral, anal, and phallic fixations occur when an issue or conflict in ...
How are fixations resolved?
So how exactly are fixations resolved? According to Freud's psychoanalytic theory, the process of transference plays an important role in treating such fixations. Essentially, an old fixation is transferred to a new one, allowing the person to consciously deal with the problem.
What did Freud believe about stage fixation?
Freud also believed that fixations could result if a particular stage left a dominant impression on an individual's personality.
What are the signs of oral fixation?
Freud may also suggest that nail-biting, smoking, gum-chewing, and excessive drinking are signs of an oral fixation. This would indicate that the individual did not resolve the primary conflicts during the earliest stage of psychosexual development, the oral stage.
How do you know if you are fixated?
If you are experiencing difficulty with acts of daily living, are noticing a reduction in your quality of life, are having distressing thoughts, and/or are engaging in harmful behaviors, it's important to reach out to your doctor right away.
When do children have oral fixations?
Oral Fixations. The oral stage tends to occur between birth and around 18 months old, during which time the oral (feeding) needs of the child are either met, overstimulated, or unmet. For example, Freud might suggest that if a child has issues during the weaning process, they might develop an oral fixation.
What is pigment?
pigment definition is expressed, A pigment is define as coloured black or white substance which is insoluble in the medium in which it is applied and imparts colour and opacity to this medium.
Classification of pigment
1. Inorganic pigment :- it is finely devided inorganic usually a stable solid which is added to vehicle to produce a stable surface coating.
What is Fe3+ in tissue staining?
Reducing substances present in tissue reduce the ferric ions (Fe3+) present in the staining solution to ferrous ions (Fe2+) which immediately combine with ferricyanide present in the staining solution to form an insoluble precipitate of ferrous ferricyanide (Turnbull’s blue)
Where is melanin found?
Melanin is the most important and is found in skin, hair, retina and parts of the CNS . Melanin can be bleached in the tissue section by treatment with hydrogen peroxide or potassium permanganate and oxalic acid . Pathologically, melanin is found in the cells of malignant melanomas and various benign naevi .
How to study minerals in tissue?
Minerals in tissue can be studied using the technique of microincineration
Can ceroid stain be differentiated?
Ceroid stains similar but can be differentiated by staining positive with ZN
How does fixation work?
The mechanism of action of fixation is through rapidly terminating all ongoing enzymatic reactions and metabolic activities by denaturing intrinsic biomolecules. In doing this, proteolytic enzymes that would otherwise digest the tissue sample via autolysis are denatured, and autolytic processes are stopped. Fixatives also protect the sample from extrinsic damage as they are toxic to most common microorganisms (bacteria in particular) that may otherwise colonize a tissue sample. In addition, many fixatives chemically alter the treated tissue to be less palatable to opportunistic microorganisms, thereby preventing the process of putrefaction.
What is fixative in biochemistry?
Fixation is a chemical process by which biological tissue is preserved to represent the sample’s in vivo state as much as possible. In order to preserve a tissue sample in a state as near to life as possible, the postmortem processes of autolysis, which is self-degradation via proteolytic enzymes, and/or putrefaction, which is the decay of organic matter through microorganism action, must be halted. An ideal fixative should preserve the given tissue sample in a way that is representative of its in vivo situation; cellular and extracellular morphology should be preserved, and the fixative should not denature proteins that are important for histopathological analysis.
How long should fixative be exposed to a tissue sample?
A fixative should be exposed to the tissue sample for as long as is needed for the solution to completely penetrate the sample. For immersion fixation, certain factors such as density of the tissue sample, rate of penetration, and temperature must be taken into consideration. It is important to note that rate of penetration and rate of fixation are two completely different processes of a fixative, with the latter proceeding slower than the former. A general rule of thumb to apply for the rate of penetration is 1 mm/hour. A fixation time of 24 hours is recommended for NBF-treated samples.
What is the best fixative for histology?
A number of fixatives exists and the use of a particular type is dictated by the downstream analysis. For histology, the most effective and commonly used fixatives are aldehyde-based. The following fixatives are recommended for H&E staining, and most IHC markers and special stains: 1 Neutral Buffered Formalin (NBF): A 10% formaldehyde buffer solution, pH 7.0-7.4 is commonly used in most laboratories. Immediately after surgery, tissue is completely immersed in 10% NBF solution and timed. A ready-to-use solution is available from various vendors in the US. The timing of fixation determines optimal fixation as discussed further. 2 Paraformaldehyde (PFA) solution: Freshly prepared 4% PFA solution produces similar results and is cost effective. Due to its fast degradation, this solution is prepared fresh each time before use.
What is the mechanism of formaldehyde?
Formaldehyde’s mechanism of fixation is through cross-linking, or creating covalent chemical bonds, between amino acid residues, mostly commonly that of amino acid lysine residues ( side chain amino groups of lysine), which result in methylene bridges. Cross-linking of formaldehyde can also occur between the aminomethylol groups and phenol, indole, and imidazole side chains. Furthermore, formaldehyde acts on a variety of amino acids, such as lysine, arginine, tyrosine, asparagine, histidine, glutamine, and serine. Cross-linking fixatives maintain internal structures of a sample and do not harm the structure of the protein significantly. The use of formaldehyde is favorable as it maintains morphology of the tissue sample and secondary and tertiary protein structure are unaffected and thus preserved. It has been proposed that formaldehyde is an effective fixative because of its fast penetration speed.
How long should fixative be left out of tissue?
Generally, it is not recommended to fix the tissue for more than 36 hours to avoid over-fixation. Both are problems that require their own solutions and must be avoided when fixing a tissue sample. The duration of the exposure of a sample to the fixative is thus a very important issue that must be carefully calibrated.
How long does it take to fix a tissue?
4-5 mm), and use ample amount of fixative, making sure tissue is completely immersed in the fixative. Fixation must be performed for no more than 24-36 hours depending on the size of tissue. Timing of the exposure of a sample to the fixative is important and must be calibrated.
Where is pigment dyestuff used?
They are dyestuffs that can be used for almost all fiber types and mixtures. The difficulties encountered in printing with other dyestuffs do not exist in these dyestuffs. It is preferred because of the low cost of fixation and post-processing. However, it can be counted as one of the disadvantages that binders affect the attitude somewhat negatively in sensitive materials.
What is pigment digital printing?
Digital pigment printing, in its most basic definition, refers to the dyeing of the raw fabric to be cut and sewn. As it is known, there are 5 main types of ink used for fabric dyeing in the textile industry: reactive, acid, direct disperse, sublimation and pigment. All of these ink types have unique fabric bonding and processing properties.
What is the color of formalin pigment?
Formalin pigment is a brown, granular, doubly refractile deposit seen both intracellularly and extracellularly in tissues which have been fixed with a simple formalin solution, such as formal-saline. It is also known as acid formaldehyde hematin, as it is formed from hemoglobin by the action of formaldehyde at acid pH. The hematin being referred to in this context is the derivative of hemoglobin and not the oxidation product of hematoxylin, called hematein.
How to stop formalin from forming?
Formalin pigment may be easily stopped from forming by using 10% neutral buffered formalin (NBF) as the fixative . Since its formation is dependent on an acidic pH, buffering to pH7 effectively stops it. However, it may still form if tissues are stored in NBF for very extended periods without changing the solution. The NBF should be changed every six months at a minimum. Doing so effectively stops formalin pigment from forming.
Can you remove pigment from slides?
In small amounts the pigment does not interfere with slide examination, but large amounts can be distracting. It may be removed from sections prior to staining quite easily by immersing in ethanolic picric acid, a method given below. It may also be removed with alkalis such as 1% sodium hydroxide in absolute ethanol, but these very frequently cause sections to detach from slides and should be avoided.
When to use dissecting in fixative?
Dissecting in fixative can be used if manipulation of the specimen is time consuming. Ideal size of the specimen . or less (actual size). If the specimen floats, it must be submerged.
How to fix a tissue that floats?
In some cases, this may be done by dipping the specimen in a wetting agent briefly before fixation or adding a wetting agent to the fixative solution. If a wetting agent is added to the fixative, then try to transfer the specimen to fresh fixative as soon as possible. Since trapped air is often the cause of tissue floating in the fixative, air can sometimes be removed by partial vacuum. However, this is sometimes damaging to the specimen. The most gentle approach is simply to put a plug of Kimwipe below the surface of the fixative, thereby trapping the specimen beneath the surface of the fixative solution.
How long should osmium fixation be done?
All osmium fixation should be conducted in the cold for up to 2 hours -- no longer.
How long does glutaraldehyde fixate?
Glutaraldehyde fixation can take place at room temperature or in the refrigerator for 2 hours (for extrememely small material), 6 hours (standard) or more if necessary.
What is the chemical removal of water from a specimen?
DEHYDRATION . Dehydration is the chemical removal of water from the specimen. Common dehydrating fluids are ethanol and acetone. The potential problems of dehydration are shrinkage of the specimen, plasmolysis, and removal of soluble components from the specimen.
Can you put a plug of Kimwipe on a fixative?
However, this is sometimes damaging to the specimen. The most gentle approach is simply to put a plug of Kimwipe below the surface of the fixative, thereby trapping the specimen beneath the surface of the fixative solution. Once the specimen is fixed, use the same vial throughout preparation.
Can you use a vial before a specimen change?
Once the specimen is fixed, use the same vial throughout preparation. Simply decant (or pipet) the contents of the vial before each change. Some people prefer to use an aspirator to speed this process. Since tissue lost in the aspirator is irretrievable, beginners would be advised not use the aspirator until they are experienced with handling material.
