Fixation in tissue processing

The present study is about Fixation of tissue. It is done for several reasons. One reason is to kill the tissue so that postmortem decay (autolysis and putrefaction) is prevented (Carson and Hladik, 2009). Fixation preserves a sample of biological material (tissue or cells) as close to its natural state as possible in the process of preparing tissue for examination. To achieve this, several conditions usually must be met. In the fields of histology, pathology, and cell biology, fixation is a chemical process by which biological tissues are preserved from decay, thereby preventing autolysis or putrefaction. Fixation terminates any on going biochemical reactions, and may also increase the mechanical strength or stability of the treated tissues.First, a fixative usually acts to disable intrinsic biomolecules particularly proteolytic enzymes—which otherwise digests or damages the sample. Second, a fixative typically protects a sample from extrinsic damage. Fixatives are toxic to most common microorganisms (bacteria in particular) that might exist in a tissue sample or which might otherwise colonise the fixed tissue. In addition, many fixatives chemically alter the fixed material to make it less palatable (either indigestible or toxic) to opportunistic microorganisms. Finally, fixatives often alter the cells or tissues on a molecular level to increase their mechanical strength or stability. This increased strength and rigidity can help preserve the morphology (shape and structure) of the sample as it is processed for further analysis.