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Difference between revisions of "Tissue fixation"
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my contribution from ganfyd.org (now inactive), slightly modified
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*May be written (incorrectly) as "formulin". | *May be written (incorrectly) as "formulin". | ||
*Formaldehyde + methanol. | *Formaldehyde + methanol. | ||
Formaldehyde is often supplied as a 37% w/v solution. To prevent polymerisation of formaldehyde, methanol is added. The resulting solution is often referred to as formalin. This can be further diluted and buffered to produce 10% formalin (equivalent to 4% formaldehyde). This concentration is often used as a fixative and preservative for histological specimens. It gives tissues a firmer texture, making subsequent cut-up easier and also stops autolysis and necrosis of the tissue by inactivating micro-organisms and proteolytic enzymes. Poorly fixed tissue stains unreliably and certain features may be lost. Mitotic figures, for instance, are easily lost in poorly fixed tissue. Formalin is also used to preserve prosected and dissected cadavers. As a rule of thumb, fixation occurs at about 1 mm per hour, but the reality is more complex as fixation lags behind diffusion and fixation also changes the tissue properties, slowing diffusion.<ref name="pmid22483550">{{cite journal |vauthors=Buesa RJ, Peshkov MV |title=How much formalin is enough to fix tissues? |journal=Ann Diagn Pathol |volume=16 |issue=3 |pages=202–9 |date=June 2012 |pmid=22483550 |doi=10.1016/j.anndiagpath.2011.12.003 |url=}}</ref> | |||
Formalin cross-links sections of the peptide chains of proteins as well as nucleic acids. The effect on the former alters epitopes, which means that antibodies designed for fresh tissue may not work with fixed tissue. The cross-linking process can be partially reversed with various methods of antigen retrieval. The effect on nucleic acids is to reduce DNA quality. | |||
=Fixing marking dye= | =Fixing marking dye= | ||