Fixation and Fixative Prepared by Reem Aldossari THE

Fixation and Fixative Prepared by : Reem Aldossari

THE GENERAL VISCRA OF THE RAT

Definition of Fixation • In the fields of histology, pathology, and cell biology, fixation is a chemical process by which biological tissues are preserved from decay, either through autolysis or putrefaction. • Fixation terminates any ongoing biochemical reactions, and may also increases the mechanical strength or stability of the treated tissues.

Purpose of fixation • • The purpose of fixation is to preserve 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 must usually be met. The aims of fixation are: 1. 2. 3. 4. 5. Prevent postmortem (PM) degeneration Prevent autolysis. It is effective against hydrolytic enzymes Stop the bacterial effect Harden the tissues, as fixation causes coagulation of proteins Fixation has a mordanting effect, facilitating subsequent staining of tissues.

Features of fixatives • First, a fixative usually acts to disable intrinsic biomolecules – particularly proteolytic enzymes – which would otherwise digest or damage the sample. • Second, a fixative will typically protect a sample from extrinsic damage. Fixatives are toxic to most common microorganisms (bacteria in particular) particular which might exist in a tissue sample or which might otherwise colonise the fixed tissue. • 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 such as Nuclear Morphometry System

Characteristics of a good fixative 1. 2. 3. 4. It must kill the cell quickly without shrinkage or swelling It must penetrate the tissue rapidly It must inhibit bacterial decay and autolysis Harden the tissue and render it insensitive to subsequent treatment as staining 5. It should allow tissue to be stored for long time 6. It should be simple to prepare and economical is use.

Preparation of fixatives: Neutral buffered formalin 10%: 900 ml 100 ml

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