HT Microtomy & Sectioning Techniques 3 — Questions and Answers
Question 1: During cryostat sectioning, tissues exhibit excessive tearing. Which adjustment is most appropriate?
- Raise the cryostat cabinet temperature closer to 0°C (Correct answer)
- Lower the cryostat cabinet temperature further below 0°C
- Increase the antiroll plate pressure
- Switch to a vibratome
Correct answer: Raise the cryostat cabinet temperature closer to 0°C
Fatty or soft tissues tear when too cold; raising the cryostat temperature (toward –10°C from –25°C) softens the tissue enough for clean cutting.
Question 2: The clearance angle on a microtome knife is defined as the angle between:
- The bevel face and the vertical plane of the block (Correct answer)
- The cutting edge and the section surface
- The knife back and the microtome arm
- The two bevel faces of the knife
Correct answer: The bevel face and the vertical plane of the block
The clearance angle is the angle between the bevel face of the knife and the vertical face of the tissue block, determining how freely sections pass under the knife.
Question 3: Which embedding medium is most commonly used for sectioning unfixed, fresh brain tissue to preserve enzyme activity for histochemistry?
- Paraffin wax
- Optimal cutting temperature (OCT) compound (Correct answer)
- Epoxy resin
- Celloidin
Correct answer: Optimal cutting temperature (OCT) compound
OCT compound is the standard cryostat embedding medium for fresh tissue enzyme histochemistry because it supports tissue without chemical fixation.
Question 4: A 'venetian blind' artifact in paraffin sections (alternating light and dark lines parallel to the cut) is caused by:
- A nick in the knife edge (Correct answer)
- Excessive water bath temperature
- Insufficient clearing of tissue
- Too much pressure on the antiroll plate
Correct answer: A nick in the knife edge
A nick or chip in the knife edge creates a streak or venetian-blind pattern running the full length of each section.
Question 5: When sectioning decalcified bone, which knife profile and clearance angle combination is most appropriate?
- Plano-concave knife, 5–10° clearance (Correct answer)
- Biconcave knife, 15–20° clearance
- Wedge knife, 2–3° clearance
- Tool-edge knife, 25–30° clearance
Correct answer: Plano-concave knife, 5–10° clearance
A plano-concave knife with a 5–10° clearance angle provides the balance of support and sharpness needed for moderately hard decalcified bone.
Question 6: What is the primary purpose of chilling the paraffin block on ice or a cold plate before sectioning?
- To harden the paraffin and reduce tissue compression (Correct answer)
- To prevent the block from sticking to the microtome chuck
- To increase section transparency on the water bath
- To facilitate ribbon formation by warming the cutting edge
Correct answer: To harden the paraffin and reduce tissue compression
Chilling firms the paraffin, reducing compression and helping produce consistently flat, uniform sections.
Question 7: Celloidin (nitrocellulose) embedding and sectioning is particularly advantageous for which tissue type?
- Soft lymph node tissue
- Large whole-eye specimens (Correct answer)
- Fresh frozen brain sections
- Routine needle biopsy cores
Correct answer: Large whole-eye specimens
Celloidin is traditionally used for large, fragile specimens like whole eyes because it provides excellent support without the heat required for paraffin.
HT Microtomy & Sectioning Techniques 3
During cryostat sectioning, tissues exhibit excessive tearing.
Which adjustment is most appropriate?