What Are The Characteristics Of A Good Fixative?

What is ideal fixative?

An ideal fixative should: Preserve the tissue and cells as life-like as possible, without any shrinking or swelling and without distorting or dissolving cellular constituents.

Stabilize and protect tissues and cells against the detrimental effects of subsequent processing and staining procedures..

Why is fixation The key to good histopathology?

A well organized pathology museum should serve many functions, thus tissue fixation before plastination is of the utmost importance. Fixation is required to prevent putrefaction and autolysis, and to preserve and harden to a lifelike state. Fixation agents are often chemical.

What are the two types of fixation?

Mechanism 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 is meant by 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.

What is the most common fixative used in histology?

1. Phosphate buffered formalin. The most widely used formaldehyde-based fixative for routine histopathology. The buffer tends to prevent the formation of formalin pigment.

What 3 factors can affect tissues?

Factors Affecting Tissue ProcessingTissue size (biopsy versus resection)Tissue thickness.Tissue density.Lipid content in tissue.

What are the types of fixation?

Chemical fixationCrosslinking fixatives – aldehydes. Crosslinking fixatives act by creating covalent chemical bonds between proteins in tissue. … Precipitating fixatives – alcohols. … Oxidizing agents. … Mercurials. … Picrates. … HOPE fixative. … Acidity or basicity. … Osmolarity.More items…

What is a fixative solution?

Fixative: A medium such as a solution or spray that preserves specimens of tissues or cells. Most biopsies and specimens removed at surgery are fixed in a solution such as formalin (dilute formaldehyde) before further processing takes place.

What are the steps involved in tissue processing?

Overview of the steps in tissue processing for paraffin sectionsObtaining a fresh specimen. Fresh tissue specimens will come from various sources. … Fixation. The specimen is placed in a liquid fixing agent (fixative) such as formaldehyde solution (formalin). … Dehydration. … Clearing. … Wax infiltration. … Embedding or blocking out.

What is physical fixation?

Fixation is the essential first step in preserving cellular structures with the goal of keeping them as “lifelike” as possible. … Tissues are immersed in a fixative that kills and stabilizes the cell contents. Physical fixation can include microwaving and cryopreserving samples to rapidly inactivate cellular activity.

What are the factors affecting fixation?

The number of factors affecting the fixation process includes buffering, penetration, volume, temperature and concentration. In fixation pH is critical.

What is simple fixative?

Simple Fixatives – These fixatives are made up of simple chemical compounds and take more time for the fixation of tissues. For example, Formalin, Picric acid, Mercuric oxide, osmic acid, Osmium tetroxide etc. … For example, Susa fluid, Carnoy’s fluid, Bouin’s Fluid, Formal saline, buffered formalin etc.

What is the purpose of fixative?

A fixative is a stabilizing or preservative agent: Dye fixatives or mordants, are chemical substances used in processing fabrics to create circumstances in the micro-substrates causing dye molecules to adhere and remain that way.

What is secondary fixation?

Secondary fixation is the term used for the practice of initially fixing with 10% formalin, then refixing with another fixative. The second fiixative refixes the tissue so that some of its characteristics can be obtained.

How is fixation done?

Fixation of tissues can be achieved by chemical or physical means. … Chemical fixation is usually achieved by immersing the specimen in the fixative (immersion fixation) or, in the case of small animals or some whole organs such as a lung, by perfusing the vascular system with fixative (perfusion fixation).

What is the principle of fixation?

The basic aims of fixation are the following: To preserve the tissue nearest to its living state. To prevent any change in shape and size of the tissue at the time of processing. To prevent any autolysis.

How fast does formalin penetrate tissue?

For 10% formalin K = 0.78. This means that your formalin fixative should not be expected to penetrate more than say 1 mm in an hour and it will take approximately 25 hours to penetrate to the centre of a 10 mm thick specimen , i.e. 5 mm ( = 5² hours).

What is coagulant fixative?

Coagulant fixatives remove water from tissues leading to coagulation and denaturalization of proteins, mostly in the extracellular matrix. Cross-linking fixatives form chemical bonds between molecules of the tissue. … They are mainly cross-linking fixatives and some coagulant fixatives.