Tissue Fixation and Decalcification Flashcards
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Read the first 7 Tissue Fixation and Decalcification flashcards as text
What is the primary purpose of tissue fixation in histology?
Answer: To prevent autolysis and putrefaction
Fixation prevents autolysis (self-digestion by intracellular enzymes) and putrefaction (bacterial decomposition) by stabilizing tissue proteins and halting enzymatic activity.
Which fixative is considered the standard routine fixative used in most histopathology laboratories?
Answer: 10% neutral buffered formalin
10% neutral buffered formalin (NBF) is the universal standard fixative because it preserves tissue morphology well and is compatible with most staining and molecular applications.
What is the approximate formaldehyde concentration in a solution labeled '10% neutral buffered formalin'?
Answer: 3.7–4% formaldehyde
10% formalin is a 1:10 dilution of the 37–40% formaldehyde stock solution, yielding an actual formaldehyde concentration of approximately 3.7–4%.
What is the primary chemical mechanism by which formalin fixes tissue?
Answer: Formation of methylene bridges that cross-link proteins
Formalin reacts with amino groups of proteins to form methylene bridges, creating a stable cross-linked protein network that preserves tissue architecture.
Bouin's fixative is particularly well-suited for which type of tissue specimen?
Answer: Testicular and gastrointestinal biopsies
Bouin's fixative (picric acid, formalin, glacial acetic acid) provides excellent cytological detail, especially for testicular and gastrointestinal biopsies.
According to CAP guidelines, what is the recommended fixation time range for standard surgical resection specimens in 10% NBF?
Answer: 6–72 hours
CAP guidelines recommend a minimum of 6 hours and a maximum of 72 hours of fixation in 10% NBF to ensure adequate protein cross-linking, particularly important for breast cancer biomarker testing.
Which fixative is specifically required for optimal ultrastructural preservation in electron microscopy?
Answer: Glutaraldehyde
Glutaraldehyde (2–4%) is the fixative of choice for electron microscopy because its bifunctional aldehyde groups provide superior cross-linking and ultrastructural preservation.