Memory tree Flashcards
Most widely used fixatives
10% Formalin
A polymerized form of formaldehyde, usually obtain as a white powder, which depolymerizes back to formalin when heated.
PARAFORMALDEHYDE
Made up of two formaldehyde residues, linked by three carbon chains.
Glutaraldehyde
Excellent trichome and brilliant metachromatic staining.
Best for tissue photography
Always leaves a brown precipitate
Mercuric Salts
Most common metallic fixative
Penetrates poorly and produces shrinkage of tissues, so it is usually combined with other fixative agents.
Mercuric Chloride
Good cytoplasmic fixative
For carbohydrates
Chromates
Best for electron microscopy
Good cytoplasmic (golgi bodies & mitochondria) result but poor nuclear staining
Osmium tetroxide
Causes denaturation & precipitation of protein by removal of hydrogen bond leading to dehydration.
Rapidly denatures and precipitates proteins by destroying hydrogen and other bonds.
Alcohol Fixatives
Used in strong saturated aqueous solution
Leaves a yellow stain to the tissue
Excellent cytoplasmic fixative for demonstration of glycogen.
Best for trichome staining
Highly explosive in the dry form
Pitric Acid
Recommended for mucopolysaccharides and fixes connective tissue mucin.
4% aqueous solution of basic lead nitrate
Lillie’s alcoholic lead nitrate formalin
LEAD
Fixes and precipitates nucleoproteins.
GLACIAL ACETIC ACID FIXATIVES
Precipitates proteins.
Poor penetration
Combined with other fixatives
Marked swelling of tissue
TRICHLOROACETIC ACID
Used at iced cold temperature ranging from -5’C to 4’C.
Histochemical
Rapid fixation for brain tissues
0-5C
ACETONE
It involves thermal coagulation of tissue proteins for rapid diagnosis, usually employed or frozen tissue sections and preparation of bacteriologic smears
HEAT FIXATION
A form of secondary fixation whereby a primarily fixed tissue is placed in aqueous solution of 2.5-3% potassium dichromate for 24 hours.
POST-CHROMATIZATION
