Tissue Fixation for Histological Examination 50 FAQs and 50 MCQs:
Tissue Fixation for Histological Examination 50 FAQs:
Why is tissue fixation important in histopathology?
Tissue fixation preserves cellular and extracellular structures, prevents enzymatic degradation, and maintains tissue morphology for accurate histological examination.
What are the primary goals of tissue fixation?
The goals include maintaining morphological features, preventing autolysis, preserving molecular components, and ensuring consistent staining results.
What are the main mechanisms of tissue fixation?
Fixation mechanisms include covalent cross-linking, dehydration, coagulation, salt formation, and heat-induced stabilization.
What are the disadvantages of formaldehyde fixation?
Disadvantages include antigen loss, tissue shrinkage/swelling, and reduced immunorecognition in immunohistochemical staining.
How does heat-induced epitope retrieval (HIER) improve immunohistochemistry?
HIER reverses formaldehyde-induced antigen masking, allowing better detection of antigens in fixed tissues.
What are the challenges of analyzing mRNA and DNA from formalin-fixed tissues?
Formalin fixation can cause cross-linking and fragmentation of nucleic acids, making extraction and analysis difficult.
What is the most commonly used fixative in diagnostic pathology?
10% neutral buffered formalin (NBF) is the most widely used fixative due to its ability to preserve tissue morphology and support staining.
What are the characteristics of an ideal fixative?
An ideal fixative should preserve tissue morphology, support molecular analysis, penetrate tissues quickly, and be safe and cost-effective.
What are the effects of fixation on tissue staining?
Fixation can cause color variations, shrinkage/swelling, and artifacts in histochemical and immunohistochemical staining.
What are physical methods of fixation?
Physical methods include heat fixation, microwave fixation, freeze-drying, and freeze substitution.
How does microwave fixation work?
Microwave fixation accelerates chemical fixation by increasing molecular movement and temperature, reducing fixation time.
What are the risks of microwave fixation?
Microwave fixation can produce harmful vapors, requiring proper ventilation or specialized equipment.
What is freeze-drying in tissue fixation?
Freeze-drying removes water from tissues at low temperatures, preserving soluble molecules for research purposes.
What are the main categories of chemical fixatives?
Chemical fixatives are categorized as coagulant, cross-linking, and compound fixatives.
What are coagulant fixatives?
Coagulant fixatives, like ethanol and acetone, denature proteins by removing water, causing protein precipitation.
What are cross-linking fixatives?
Cross-linking fixatives, such as formaldehyde and glutaraldehyde, form covalent bonds between proteins and nucleic acids.
What are compound fixatives?
Compound fixatives combine multiple mechanisms, such as alcoholic formalin, which uses both dehydration and cross-linking.
What is the role of formaldehyde in fixation?
Formaldehyde forms hydroxymethyl groups and cross-links, stabilizing proteins and nucleic acids while preserving tissue structure.
What are the limitations of glutaraldehyde fixation?
Glutaraldehyde causes extensive cross-linking, which can hinder immunohistochemistry and requires small tissue samples.
How does osmium tetroxide fixation work?
Osmium tetroxide reacts with lipids and proteins, preserving membranes and providing contrast for electron microscopy.
What are the safety concerns with mercuric chloride fixation?
Mercuric chloride is toxic, forms harmful pigments, and poses environmental disposal challenges.
What are the advantages of zinc-based fixatives?
Zinc-based fixatives improve nuclear detail, enhance immunohistochemistry, and are less toxic than mercury-based fixatives.
What is the role of pH in fixation?
pH affects the reactivity of fixatives; neutral pH (7.2–7.4) is optimal for formaldehyde fixation to prevent pigment formation.
How does fixation time affect tissue quality?
Insufficient fixation can lead to poor preservation, while over-fixation can cause excessive cross-linking and antigen masking.
What is the relationship between tissue size and fixation time?
Fixation time increases with tissue thickness; larger specimens require longer fixation to ensure complete penetration.
How does temperature affect fixation?
Higher temperatures accelerate fixation by increasing molecular movement and reaction rates.
What is the optimal concentration of formaldehyde for fixation?
A 10% formalin solution (4% formaldehyde) is optimal, as higher concentrations can cause excessive hardening and shrinkage.
What is the role of osmolality in fixation?
Hypertonic or hypotonic fixatives can cause tissue shrinkage or swelling; slightly hypertonic solutions (400–450 mOsm) are ideal.
What additives can improve fixation?
Additives like calcium chloride, potassium thiocyanate, and detergents can enhance tissue morphology and fixation quality.
What are the effects of fixation on lipids?
Lipids are often lost during fixation, except with specialized fixatives like osmium tetroxide, which preserves lipid membranes.
What are the effects of fixation on carbohydrates?
Carbohydrates are generally unaffected by fixation, but some fixatives can cross-link glycoproteins.
What are the effects of fixation on nucleic acids?
Fixation can cross-link nucleic acids, making them less accessible for molecular analysis unless specialized methods are used.
What are the best fixatives for immunohistochemistry?
Zinc-based fixatives and neutral buffered formalin are preferred for preserving antigen immunorecognition.
What are the best fixatives for electron microscopy?
Glutaraldehyde and osmium tetroxide are commonly used for ultrastructural preservation in electron microscopy.
What are the best fixatives for fatty tissues?
Alcoholic formalin is effective for fatty tissues, as it extracts lipids and improves tissue penetration.
What are the best fixatives for lymphoid tissues?
B5 fixative and zinc-based formalin are recommended for lymphoid tissues due to their ability to preserve nuclear detail.
What are the best fixatives for renal biopsies?
Renal biopsies are typically divided and fixed in NBF for histology, glutaraldehyde for electron microscopy, and snap-frozen for immunofluorescence.
What are the best fixatives for muscle biopsies?
Muscle biopsies are fixed in NBF for routine histology and enzyme histochemistry.
What are the best fixatives for brain tissue?
Brain tissue is typically fixed in NBF, with perfusion techniques or microwave enhancement to reduce fixation time.
What are the best fixatives for lung tissue?
Lung tissue is fixed in NBF, often inflated via the trachea to preserve alveolar structure.
What are the best fixatives for eye tissue?
Eye tissue is fixed in NBF, with small windows cut into the globe to speed fixation.
What are the best fixatives for testicular tissue?
Testicular biopsies are fixed in NBF for routine histological examination.
What are the best fixatives for breast tissue?
Breast tissue is fixed in NBF for 6–72 hours to preserve biomarkers like estrogen receptors.
What are the best fixatives for DNA and RNA analysis?
Zinc-based fixatives like Z7 are recommended for preserving nucleic acids for PCR and other molecular analyses.
What are the best fixatives for glycogen preservation?
Alcoholic fixatives like Carnoy’s solution are effective for preserving glycogen.
What are the best fixatives for connective tissue stains?
Bouin’s solution is ideal for connective tissue stains due to its ability to preserve collagen and other extracellular components.
What are the best fixatives for lipid preservation?
Osmium tetroxide and formal calcium are effective for preserving lipids in tissues.
What are the best fixatives for enzyme histochemistry?
Cold acetone is commonly used for enzyme histochemistry, as it preserves enzyme activity.
What are the best fixatives for immunohistochemistry on fatty tissues?
Alcoholic formalin is effective for immunohistochemistry on fatty tissues due to its lipid-extracting properties.
What are the best fixatives for long-term tissue storage?
Neutral buffered formalin is preferred for long-term storage due to its ability to maintain tissue integrity and support future analyses.
Tissue Fixation for Histological Examination 50 MCQs:
Multiple Choice Questions (MCQs) on Tissue Fixation for Histological Examination
- What is the primary purpose of tissue fixation in histopathology?
a) To stain tissues
b) To preserve tissue morphology ✔
c) To extract DNA
d) To dehydrate tissues - Which of the following is NOT a mechanism of tissue fixation?
a) Covalent cross-linking
b) Dehydration
c) Heat-induced stabilization
d) Enzymatic digestion✔ - Which fixative is most commonly used in diagnostic pathology?
a) Ethanol
b) 10% neutral buffered formalin✔
c) Glutaraldehyde
d) Osmium tetroxide - What is a major disadvantage of formaldehyde fixation?
a) It preserves lipids
b) It causes antigen loss✔
c) It is inexpensive
d) It is non-toxic - What does heat-induced epitope retrieval (HIER) improve?
a) Tissue dehydration
b) Antigen detection in immunohistochemistry✔
c) DNA extraction
d) Lipid preservation - Which of the following is a physical method of fixation?
a) Formaldehyde fixation
b) Microwave fixation✔
c) Glutaraldehyde fixation
d) Zinc-based fixation - What is the primary role of freeze-drying in tissue fixation?
a) To cross-link proteins
b) To remove water and preserve soluble molecules✔
c) To stain tissues
d) To extract DNA - Which of the following is a coagulant fixative?
a) Formaldehyde
b) Ethanol✔
c) Glutaraldehyde
d) Osmium tetroxide - What is the main advantage of cross-linking fixatives like formaldehyde?
a) They dehydrate tissues
b) They form covalent bonds between proteins✔
c) They extract lipids
d) They are non-toxic - Which fixative is best suited for electron microscopy?
a) Ethanol
b) Formaldehyde
c) Glutaraldehyde✔
d) Acetone - What is a major safety concern with mercuric chloride fixation?
a) It is non-toxic
b) It forms harmful pigments✔
c) It is inexpensive
d) It preserves lipids - Which fixative is recommended for preserving nucleic acids for PCR analysis?
a) Formaldehyde
b) Zinc-based fixatives✔
c) Ethanol
d) Osmium tetroxide - What is the optimal pH for formaldehyde fixation?
a) 5.0–5.5
b) 6.0–6.5
c) 7.2–7.4✔
d) 8.0–8.5 - How does fixation time affect tissue quality?
a) Longer fixation always improves quality
b) Insufficient fixation leads to poor preservation✔
c) Fixation time has no effect on tissue quality
d) Over-fixation improves antigen detection - What is the relationship between tissue size and fixation time?
a) Larger tissues require shorter fixation times
b) Fixation time is independent of tissue size
c) Larger tissues require longer fixation times✔
d) Fixation time is only affected by temperature - Which of the following fixatives is best for preserving lipids?
a) Ethanol
b) Formaldehyde
c) Osmium tetroxide✔
d) Acetone - What is the main disadvantage of glutaraldehyde fixation?
a) It is non-toxic
b) It causes excessive cross-linking✔
c) It is inexpensive
d) It preserves nucleic acids - Which fixative is recommended for fatty tissues?
a) Ethanol
b) Alcoholic formalin✔
c) Formaldehyde
d) Glutaraldehyde - What is the primary role of osmium tetroxide in fixation?
a) To cross-link proteins
b) To preserve lipids and membranes✔
c) To dehydrate tissues
d) To extract DNA - Which of the following is a compound fixative?
a) Ethanol
b) Formaldehyde
c) Alcoholic formalin✔
d) Glutaraldehyde - What is the main advantage of zinc-based fixatives?
a) They are toxic
b) They improve nuclear detail✔
c) They are expensive
d) They are non-reactive - Which fixative is best for preserving glycogen?
a) Formaldehyde
b) Ethanol
c) Carnoy’s solution✔
d) Glutaraldehyde - What is the primary role of pH in fixation?
a) It affects the reactivity of fixatives✔
b) It dehydrates tissues
c) It extracts lipids
d) It has no effect on fixation - Which fixative is recommended for connective tissue stains?
a) Formaldehyde
b) Bouin’s solution✔
c) Ethanol
d) Glutaraldehyde - What is the main disadvantage of ethanol fixation?
a) It preserves lipids
b) It causes excessive shrinkage✔
c) It is non-toxic
d) It is inexpensive - Which fixative is best for preserving enzyme activity?
a) Formaldehyde
b) Cold acetone✔
c) Glutaraldehyde
d) Osmium tetroxide - What is the primary role of heat in microwave fixation?
a) To dehydrate tissues
b) To accelerate chemical fixation✔
c) To extract DNA
d) To preserve lipids - Which fixative is recommended for immunohistochemistry on fatty tissues?
a) Formaldehyde
b) Alcoholic formalin✔
c) Glutaraldehyde
d) Osmium tetroxide - What is the main disadvantage of osmium tetroxide fixation?
a) It is non-toxic
b) It is expensive and toxic✔
c) It preserves lipids
d) It is easy to use - Which fixative is best for preserving nucleic acids for molecular analysis?
a) Formaldehyde
b) Zinc-based fixatives✔
c) Ethanol
d) Glutaraldehyde - What is the primary role of freeze-drying in tissue fixation?
a) To cross-link proteins
b) To remove water and preserve soluble molecules✔
c) To stain tissues
d) To extract DNA - Which fixative is recommended for preserving lipids?
a) Ethanol
b) Formaldehyde
c) Osmium tetroxide✔
d) Acetone - What is the main disadvantage of glutaraldehyde fixation?
a) It is non-toxic
b) It causes excessive cross-linking✔
c) It is inexpensive
d) It preserves nucleic acids - Which fixative is recommended for fatty tissues?
a) Ethanol
b) Alcoholic formalin✔
c) Formaldehyde
d) Glutaraldehyde - What is the primary role of osmium tetroxide in fixation?
a) To cross-link proteins
b) To preserve lipids and membranes✔
c) To dehydrate tissues
d) To extract DNA - Which of the following is a compound fixative?
a) Ethanol
b) Formaldehyde
c) Alcoholic formalin✔
d) Glutaraldehyde - What is the main advantage of zinc-based fixatives?
a) They are toxic
b) They improve nuclear detail✔
c) They are expensive
d) They are non-reactive - Which fixative is best for preserving glycogen?
a) Formaldehyde
b) Ethanol
c) Carnoy’s solution✔
d) Glutaraldehyde - What is the primary role of pH in fixation?
a) It affects the reactivity of fixatives✔
b) It dehydrates tissues
c) It extracts lipids
d) It has no effect on fixation - Which fixative is recommended for connective tissue stains?
a) Formaldehyde
b) Bouin’s solution✔
c) Ethanol
d) Glutaraldehyde - What is the main disadvantage of ethanol fixation?
a) It preserves lipids
b) It causes excessive shrinkage✔
c) It is non-toxic
d) It is inexpensive - Which fixative is best for preserving enzyme activity?
a) Formaldehyde
b) Cold acetone✔
c) Glutaraldehyde
d) Osmium tetroxide - What is the primary role of heat in microwave fixation?
a) To dehydrate tissues
b) To accelerate chemical fixation✔
c) To extract DNA
d) To preserve lipids - Which fixative is recommended for immunohistochemistry on fatty tissues?
a) Formaldehyde
b) Alcoholic formalin✔
c) Glutaraldehyde
d) Osmium tetroxide - What is the main disadvantage of osmium tetroxide fixation?
a) It is non-toxic
b) It is expensive and toxic✔
c) It preserves lipids
d) It is easy to use - Which fixative is best for preserving nucleic acids for molecular analysis?
a) Formaldehyde
b) Zinc-based fixatives✔
c) Ethanol
d) Glutaraldehyde - What is the primary role of freeze-drying in tissue fixation?
a) To cross-link proteins
b) To remove water and preserve soluble molecules✔
c) To stain tissues
d) To extract DNA - Which fixative is recommended for preserving lipids?
a) Ethanol
b) Formaldehyde
c) Osmium tetroxide✔
d) Acetone - What is the main disadvantage of glutaraldehyde fixation?
a) It is non-toxic
b) It causes excessive cross-linking✔
c) It is inexpensive
d) It preserves nucleic acids - Which fixative is recommended for fatty tissues?
a) Ethanol
b) Alcoholic formalin✔
c) Formaldehyde
d) Glutaraldehyde
