Histotechnology: microtomes and knives

14 Kerala PSC Lab Technician Gr II practice questions on Histotechnology: microtomes and knives, part of Pathology. The first 14 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Medium

   Why have disposable blades largely replaced reusable steel knives for paraffin sectioning?

   1. AThey cut undecalcified bone easily
   2. BThey cannot cause cut injuries
   3. CThey need no honing or stropping
   4. DThey need no clearance angle

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   Answer: C · They need no honing or stropping

   Disposable blades come sharp and uniform; when one part is dull the blade is moved along or thrown away. This saves the time and skill that honing and stropping a steel knife demand, and gives consistent sections. Blades still need the correct clearance angle in the holder. Used blades are sharps and go into the white translucent puncture-proof container under the Biomedical Waste Management Rules 2016.

   • A: Thin disposable blades are not for undecalcified bone; tungsten carbide knives are used.
   • B: They are very sharp and must go into a puncture-proof sharps container.
   • D: Every blade still needs the correct clearance angle.

2. Question 2 · Medium

   In a sliding microtome, as used for celloidin sections:

   1. AThe block swings in an arc on an arm
   2. BThe block rises and falls on a wheel
   3. CThe block moves; the knife stays fixed
   4. DThe knife moves; the block stays fixed

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   Answer: D · The knife moves; the block stays fixed

   In the sliding microtome the block is clamped still and the knife, held on a carriage, slides across it along a rail. The block is raised by the set thickness before each stroke. For celloidin the knife is set obliquely and kept wet with 70% alcohol. The base sledge microtome works the other way round, with a fixed knife and a block that moves on the sledge.

   • A: A block swinging in an arc describes the rocking (Cambridge) microtome.
   • B: Up-and-down movement driven by a wheel describes the rotary microtome.
   • C: A fixed knife with a moving block describes the base sledge microtome.

3. Question 3 · Easy

   Which microtome is most widely used for cutting routine paraffin sections?

   1. ARocking microtome
   2. BFreezing microtome
   3. CRotary microtome
   4. DSledge microtome

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   Answer: C · Rotary microtome

   In the rotary (Minot) microtome, turning the handwheel moves the block up and down past a fixed knife and advances it by the set thickness at each turn. It is heavy and stable and cuts ribbons of 3-5 µm sections, so it suits routine and serial sections. The same mechanism is built into most cryostats. The rocking microtome is an older, lighter design that is now rarely used.

   • A: The rocking (Cambridge) microtome is an older, lighter instrument, now rarely used.
   • B: The freezing microtome cuts frozen, unembedded tissue.
   • D: The sledge microtome is kept for very large or hard blocks.

4. Question 4 · Hard

   After honing, a trainee examines a microtome knife under the microscope and still sees nicks all along the edge. What should be done next?

   1. AStrop it at once to remove the nicks
   2. BIncrease the clearance angle and cut
   3. CContinue honing until the nicks are gone
   4. DUse it, cutting with the least nicked part

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   Answer: C · Continue honing until the nicks are gone

   Honing grinds the edge on a hone, coarse abrasive first and then fine, until all nicks are removed and the cutting facets meet in a straight line. Stropping on leather only polishes the edge and removes the burr left by honing; it cannot grind out nicks. The edge is checked under the microscope after honing, and stropping follows only when it is free of nicks. A nicked knife scores the block and leaves scratches and splits in every section.

   • A: Stropping only polishes the edge and removes the burr; it cannot grind out nicks.
   • B: The clearance angle does not repair a damaged edge.
   • D: With nicks all along the edge, every section will be scored and split.

5. Question 5 · Easy

   The clearance angle between the knife and the block face for paraffin sections is usually about:

   1. A3-8°
   2. B45°
   3. C15°
   4. D27-32°

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   Answer: A · 3-8°

   The clearance angle is the small angle between the cutting facet of the knife and the face of the block; it stops the rest of the knife from rubbing the block. About 3-8° is used for paraffin sections. Too small an angle lets the knife press on the block and gives alternate thick and thin sections, while too large an angle makes the knife scrape and chatter. The bevel angle of the edge itself is about 27-32°.

   • B: At 45° the knife could not cut a section at all.
   • C: 15° is too steep a clearance; the knife would scrape and chatter.
   • D: 27-32° is the bevel angle of the cutting edge, not the clearance angle.

6. Question 6 · Medium

   Sections cut on a rocking (Cambridge) microtome are slightly curved rather than flat because:

   1. AThe knife is set at a very steep angle
   2. BThe knife slides across a fixed block
   3. CThe block is frozen while it is cut
   4. DThe block swings in an arc past the knife

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7. Question 7 · Easy

   A plano-concave microtome knife is traditionally used for cutting:

   1. AUltrathin sections for EM
   2. BUndecalcified bone blocks
   3. CCelloidin-embedded tissue
   4. DFrozen sections in a cryostat

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8. Question 8 · Medium

   How is the knife moved during stropping, compared with honing?

   1. AEdge first on both the strop and the hone
   2. BEdge first on the strop, back first on the hone
   3. CBack first on the strop, edge first on the hone
   4. DBack first on both the strop and the hone

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9. Question 9 · Easy

   In a rotary microtome, during cutting:

   1. AThe knife slides across a fixed block
   2. BThe block swings in an arc past the knife
   3. CThe knife and block both stay still
   4. DThe block moves vertically past a fixed knife

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10. Question 10 · Hard

    A ribbon from a rotary microtome shows sections that are alternately thick and thin, though the thickness setting is fixed at 4 µm and the blade is new. What is the most likely cause?

    1. AA loose knife or block clamp
    2. BWax that is too hard for the room
    3. CA knife edge with a single nick
    4. DTissue that was not fully dehydrated

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11. Question 11 · Easy

    Stropping of a microtome knife is done on a:

    1. ALeather strop
    2. BArkansas stone
    3. CGlass plate with abrasive
    4. DBelgian yellow hone

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12. Question 12 · Easy

    Routine paraffin sections for H&E staining are usually cut at a thickness of:

    1. A10-15 µm
    2. B0.5-1 µm
    3. C3-5 µm
    4. D20-25 µm

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13. Question 13 · Hard

    While several different blocks are cut with the same blade, every ribbon shows a fine split running lengthwise at the same distance from the left end of the blade. What should be done?

    1. AMove to an unused part of the blade
    2. BSoak the block faces on wet ice
    3. CRe-embed the blocks in fresh wax
    4. DIncrease the clearance angle sharply

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14. Question 14 · Medium

    The bevel (cutting facet) angle of a sharpened microtome knife is usually about:

    1. A3-8°
    2. B45-50°
    3. C27-32°
    4. D10-12°

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