HTL Tissue Preparation & Processing — Questions and Answers
Question 1: What is the primary purpose of tissue fixation in histology?
- To shrink the tissue for easier handling
- To prevent the tissue from decaying and preserve its structure (Correct answer)
- To soften the tissue for better sectioning
- To remove water from the tissue
Correct answer: To prevent the tissue from decaying and preserve its structure
Tissue fixation is the critical first step in tissue processing for histology. Its primary purpose is to rapidly halt all cellular processes, preventing autolysis (self-digestion) and putrefaction (bacterial decomposition) that would otherwise degrade the tissue. Fixation also stabilizes the tissue's cellular and subcellular components, preserving its architectural integrity and molecular composition for accurate microscopic examination.
Question 2: Which of the following is a common fixative used in tissue processing?
- Ethanol
- Formalin (Correct answer)
- Acetone
- Xylene
Correct answer: Formalin
Formalin, typically a 10% neutral buffered formalin solution, is the most widely used fixative in histology. It works by cross-linking proteins, which stabilizes the tissue structure and prevents degradation. Its effectiveness, affordability, and ability to preserve a broad range of tissue components make it the gold standard for routine tissue fixation.
Question 3: Why is tissue dehydration necessary in histology?
- To preserve the tissue's natural color
- To prepare the tissue for embedding in paraffin (Correct answer)
- To enhance the tissue's strength
- To make the tissue more flexible
Correct answer: To prepare the tissue for embedding in paraffin
Tissue dehydration is a necessary step in histology because paraffin wax, the embedding medium, is immiscible with water. During dehydration, water is gradually removed from the fixed tissue by passing it through a series of increasing concentrations of alcohol. This prepares the tissue to be infiltrated by clearing agents and subsequently by molten paraffin, ensuring proper embedding.
Question 4: What is the purpose of embedding tissue in paraffin?
- To prevent the tissue from becoming too hard
- To facilitate easier cutting and maintain tissue integrity (Correct answer)
- To allow the tissue to expand during sectioning
- To keep the tissue at room temperature
Correct answer: To facilitate easier cutting and maintain tissue integrity
Embedding tissue in paraffin wax is crucial for providing structural support to the delicate tissue sample. Once the paraffin solidifies, it forms a block that allows for extremely thin sections (typically 3-5 micrometers) to be cut without tearing or distorting the tissue. This process maintains the tissue's architectural integrity, which is essential for detailed microscopic examination.
Question 5: Which staining method is commonly used to differentiate between different tissue types?
- Silver stain
- Hematoxylin and eosin (H&E) stain (Correct answer)
- Periodic acid-Schiff (PAS) stain
- Giemsa stain
Correct answer: Hematoxylin and eosin (H&E) stain
The Hematoxylin and Eosin (H&E) stain is the most fundamental and widely used staining method in histology. It provides excellent morphological detail, with hematoxylin staining nuclei blue/purple and eosin staining cytoplasm and extracellular matrix pink/red. This differential staining allows pathologists to easily distinguish between various tissue types, cell structures, and identify pathological changes, making it indispensable for routine diagnosis.
Question 6: Why is sectioning important in histology?
- To remove excess embedding material
- To prepare the tissue for microscopic examination (Correct answer)
- To enhance the color of the tissue
- To preserve the tissue for long-term storage
Correct answer: To prepare the tissue for microscopic examination
Sectioning, typically performed using a microtome, involves cutting the paraffin-embedded tissue block into extremely thin slices. These thin sections are necessary because light needs to pass through the tissue for microscopic visualization. By producing transparent, uniform sections, sectioning allows for detailed examination of cellular and tissue architecture under a microscope.
HTL Tissue Preparation & Processing
What is the primary purpose of tissue fixation in histology?