Fixation and Tissue Processing Flashcards

Vocabulary-style flashcards based on lecture notes about tissue fixation, covering chemical and physical methods, specific reagents, and fixation mechanics.

Fixation

The process of killing, penetration, and hardening of tissue, achieved by stabilizing proteins to make tissues resistant to further changes.

Primary Aim of Fixation

To preserve the morphologic and chemical integrity of the cell in as life-like a manner as possible.

Heat Fixation

A physical method primarily used in microbiology to accelerate other forms of fixation and tissue processing steps, usually carried out at $120^{\circ}C$ to $180^{\circ}C$.

Microwave Heating

A method which speeds fixation and can reduce times for some gross specimens and histological sections from more than $12$ hours to less than $20$ minutes.

Freeze Drying (Quenching)

A special way of preserving tissues by rapid freezing of fresh tissue ($2\,mm$ thick) and subsequently removing iced water via desiccation in a vacuum at a higher temperature.

Freeze Substitution

A process where frozen tissue is fixed in Rossman's Formula/$1\%$ Acetone and dehydrated in Absolute Alcohol instead of vacuum drying.

Rate of Penetration

The speed at which a fixative enters the tissue; for formalin, this rate is approximately $1\,mm/hr$.

Lendrum’s Method

A method used for hard tissues (cervix, uterine, fibroid) involving immersion in $4\%$ phenol for $1-3$ days.

Additive Fixation

A mechanism where the chemical constituent of the fixative is taken in and becomes part of the tissue; examples include Formaldehyde and Mercuric chloride.

Non-additive Fixation

A mechanism where the fixing agent is not taken into the tissue but alters its composition to stabilize it; examples include Alcohol and Acetone.

Microanatomical Fixatives

Fixatives that permit the general microscopic study of tissue structures; they should never contain osmium tetroxide as it inhibits hematoxylin.

Cytological Fixatives

Fixatives used to preserve nuclear or cytoplasmic parts and specific microscopic elements of the cell.

Nuclear Fixatives

Fixatives that preserve nuclear structures, typically containing glacial acetic acid and having a pH $\\le 4.6$.

Cytoplasmic Preservatives

Fixatives that preserve cytoplasmic structures like mitochondria and Golgi bodies; they must not contain glacial acetic acid and should have a pH $> 4.6$.

10% Neutral Buffered Formalin (NBF)

The best general-purpose tissue fixative, buffered at pH $7$ using a phosphate buffer.

Paraformaldehyde

A white crystalline precipitate formed in formalin due to prolonged storage; prevented by adding $10\%$ methanol.

Acid Formaldehyde Hematin

A brownish-black pigment granule produced by the reaction between formic acid and hemoglobin in unstable formaldehyde fixatives.

Glutaraldehyde

An aldehyde fixative used at $2.5\%$ to $4\%$ that is excellent for electron microscopy, often followed by secondary fixation in osmium tetroxide.

Glyoxal

The smallest aldehyde fixative, supplied as a $40\%$ aqueous solution; it is fast-acting ($45$ min for small biopsies).

Mercuric Chloride

The most common metallic fixative, recommended for renal biopsies and tissue photography; it permits brilliant b-chromatic staining.

Heidenhain's Susa

An excellent cytologic fixative recommended for tumor skin biopsies; notably, it does not produce mercuric chloride black deposits.

Zenker's Fluid

A fixative containing mercuric chloride and glacial acetic acid, recommended for small pieces of liver, spleen, and nuclei.

Helly's Fluid (Zenker-formol)

An excellent microanatomic fixative for the pituitary gland, bone marrow, and blood-containing organs.

Regaud's Fluid (Mueller's)

A chromate fixative recommended for the demonstration of mitochondria, mitotic figures, and colloid-containing tissues.

Picric Acid

The only substance that can fix, differentiate, and stain tissue alone; it is highly explosive when dry and excellent for glycogen demonstration.

Bouin's Solution

A picric acid fixative recommended for embryos and soft structures like endometrial curettings; it is not compatible with the Feulgen reaction.

Carnoy's Fluid

A rapid alcoholic fixative (fixation time $1-3$ hours) used for chromosomes, urgent biopsies, and brain tissue for rabies diagnosis.

Osmium Tetroxide (Osmic Acid)

A fixative primarily for electron microscopy that inhibits hematoxylin and must be kept in dark-colored bottles to prevent evaporation.

Glacial Acetic Acid

A reagent that solidifies at $17^{\circ}C$, precipitates nucleoproteins, and causes tissues to swell.

Trichloroacetic Acid (TCA)

A weak decalcifying agent and fixative used for the precipitation of proteins and nucleic acids.

Secondary Fixation (Post Mordanting)

The process of placing an already fixed tissue in a second fixative to facilitate special staining or ensure hardening.

Post-chromatization

A form of fixation using $2.5\%$ to $3.5\%$ potassium dichromate for $24$ hours to act as a mordant for better staining effects.