FIXATION

Question 1

1. What is the primary purpose of fixation in histology?
   a) To stain tissues
   b) To preserve tissue structure
   c) To dehydrate tissues
   d) To mount tissues on slides

Answer 1

b) To preserve tissue structure
Explanation: The primary purpose of fixation is to preserve the structure of tissues, preventing autolysis and decay, and maintaining the tissue’s morphology for examination under a microscope.

Question 2

What is the typical concentration of formalin used for tissue fixation?
a) 5%
b) 10%
c) 20%
d) 30%

Answer 2

b) 10%
Explanation: A 10% formalin solution, which is about 4% formaldehyde, is the standard concentration used for tissue fixation in histology.

Question 3

hich of the following substances is often added to formalin to prevent the formation of formic acid?
a) Sodium phosphate
b) Sodium chloride
c) Methanol
d) Glutaraldehyde

Answer 3

c) Methanol
Explanation: Methanol is commonly added to formalin to prevent the formation of formic acid, which can cause formalin to become acidic and lead to poor tissue preservation.

Question 4

Fixation with formalin primarily affects which component of the tissue?
a) Lipids
b) Proteins
c) Nucleic acids
d) Carbohydrates

Answer 4

b) Proteins
Explanation: Formalin primarily crosslinks proteins, stabilizing the tissue structure by preserving proteins’ original state.

Question 5

Which type of fixation is often used to preserve cell morphology for electron microscopy?
a) Chemical fixation
b) Heat fixation
c) Cryofixation
d) Vapor fixation

Answer 5

c) Cryofixation
Explanation: Cryofixation rapidly freezes tissue, preserving cell morphology and ultrastructures for electron microscopy.

Question 5

What is the effect of prolonged fixation on tissue samples?
a) Improved staining quality
b) Increased tissue brittleness
c) Enhanced preservation
d) No significant effect

Answer 5

b) Increased tissue brittleness
Explanation: Prolonged fixation can make tissues brittle, complicating sectioning and staining.

Question 6

Which fixative is known for its ability to preserve nucleic acids in tissues?
a) Ethanol
b) Acetone
c) Carnoy’s solution
d) Glutaraldehyde

Answer 6

c) Carnoy’s solution
Explanation: Carnoy’s solution is effective at preserving nucleic acids, making it useful for studies involving DNA and RNA.

Question 6

What is the primary disadvantage of using osmium tetroxide as a fixative?
a) High toxicity
b) Poor penetration
c) Limited protein preservation
d) Lack of staining compatibility

Answer 6

Answer: a) High toxicity
Explanation: Osmium tetroxide is highly toxic, requiring careful handling, despite its effectiveness in preserving lipids and cell membranes.

Question 6

Which fixative is known for its ability to preserve ultrastructures such as cell organelles?
a) Formaldehyde
b) Glutaraldehyde
c) Acetone
d) Ethanol

Answer 6

b) Glutaraldehyde
Explanation: Glutaraldehyde is particularly effective at preserving ultrastructures, making it ideal for electron microscopy.

Question 7

Why is glutaraldehyde often used in combination with osmium tetroxide?
a) To enhance lipid fixation
b) To improve protein crosslinking
c) To prevent tissue hardening
d) To preserve both proteins and membranes

Answer 7

d) To preserve both proteins and membranes
Explanation: The combination of glutaraldehyde and osmium tetroxide is effective in preserving both proteins and cell membranes, which is crucial for electron microscopy.

Question 7

What is the recommended time for optimal fixation in 10% formalin?
a) 1-2 hours
b) 6-8 hours
c) 12-24 hours
d) 48-72 hours

Answer 7

c) 12-24 hours
Explanation: Optimal fixation in 10% formalin typically takes 12-24 hours, ensuring thorough preservation of tissue structures.

Question 7

Which of the following fixatives is most suitable for immunohistochemical studies?
a) Formaldehyde
b) Glutaraldehyde
c) Acetone
d) Zinc formalin

Answer 7

d) Zinc formalin
Explanation: Zinc formalin fixatives are often used for immunohistochemical studies due to their ability to preserve antigens effectively.

Question 7

Which component of Bouin’s fixative is responsible for its ability to preserve soft tissues well?
a) Picric acid
b) Formaldehyde
c) Acetic acid
d) Glutaraldehyde

Answer 7

a) Picric acid
Explanation: Picric acid in Bouin’s fixative preserves soft tissues effectively and provides excellent staining results.

Question 7

Which fixative is preferred for preserving glycogen in tissues?
a) Formaldehyde
b) Carnoy’s solution
c) Bouin’s solution
d) Acetone

Answer 7

b) Carnoy’s solution
Explanation: Carnoy’s solution is excellent for preserving glycogen in tissues, making it a choice fixative for carbohydrate studies.

Question 7

What is a common use of acetone in histological fixation?
a) Fixing brain tissues
b) Fixing enzyme histochemistry samples
c) Preserving lipids
d) Fixing immunohistochemistry samples

Answer 7

b) Fixing enzyme histochemistry samples
Explanation: Acetone is commonly used in the fixation of tissues for enzyme histochemistry because it preserves enzyme activity.

Question 7

What is the role of acetic acid in fixatives like Bouin’s solution?
a) Protein denaturation
b) Neutralization of formalin
c) Tissue swelling
d) Stain enhancement

Answer 7

c) Tissue swelling
Explanation: Acetic acid in Bouin’s solution causes tissue swelling, helping to counteract the shrinkage effect of other components.

Question 8

Which of the following fixatives is least likely to cause tissue shrinkage?
a) Formalin
b) Glutaraldehyde
c) Bouin’s solution
d) Acetone

Answer 8

c) Bouin’s solution
Explanation: Bouin’s solution minimizes tissue shrinkage due to the combined action of picric acid and formaldehyde.

Question 8

What is the effect of fixation on tissue antigenicity?
a) It enhances antigenicity
b) It can reduce antigenicity
c) It has no effect on antigenicity
d) It only affects lipid antigens

Answer 8

b) It can reduce antigenicity
Explanation: Fixation can reduce antigenicity by masking or altering epitopes, which may require antigen retrieval techniques in immunohistochemistry.

Question 8

Which of the following is a disadvantage of using glutaraldehyde as a fixative?
a) Poor lipid preservation
b) High cost
c) Slow penetration
d) Toxicity

Answer 8

c) Slow penetration
Explanation: Glutaraldehyde penetrates tissues more slowly than formalin, which can limit its use in some applications.

Question 8

What type of fixation is typically used to study lipids in tissues?
a) Osmium tetroxide fixation
b) Formalin fixation
c) Alcohol fixation
d) Glutaraldehyde fixation

Answer 8

a) Osmium tetroxide fixation
Explanation: Osmium tetroxide is used for lipid fixation because it reacts with unsaturated fatty acids, effectively preserving lipids.

Question 8

What is the primary fixative used for light microscopy of routine histological sections?
a) Bouin’s solution
b) Formalin
c) Glutaraldehyde
d) Osmium tetroxide

Answer 8

b) Formalin
Explanation: Formalin is the primary fixative used for routine histological sections prepared for light microscopy due to its versatility and effectiveness.