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Question 1

What is microtomy?

Answer 1

A paraffin embedded tissue is trimmed and cut uniformly.

Consists of 3 essential parts: Block Holder, Knife Carrier and Knife, Pawl, Ratchet Feed Wheel, and Adjustment Screws.

Question 2

What are the essential parts of a microtome?

Answer 2

Block Holder, Knife Carrier and Knife, Pawl, Ratchet Feed Wheel, and Adjustment Screws.

Question 3

What is the principle of a microtome?

Answer 3

A spring balanced teeth or pawl turns a ratchet feed wheel connected to a micrometer screw, moving the tissue block towards the knife for cutting sections at uniform thickness.

Question 4

What is a rocking microtome?

Answer 4

Invented by PALDWELL TREFALL, it is the simplest microtome with a heavy base and 2 arms, used for cutting paraffin embedded tissue sections in large blocks.

Section cut produces a slightly curved plane with a thickness of 10-12u.

Question 5

What is a rotary (Minot) microtome?

Answer 5

Invented by CHARLES MINOT, it is the most common type used for both routine and research laboratories, cutting paraffin embedded tissues between 3-5 um thickness.

Knife is fixed in a horizontal position.

Question 6

What is a sliding microtome?

Answer 6

Developed by ADAMS for large refractory blocks, it is used for cutting celloidin embedded tissue and has 2 types: Base-sledge and Standard S.M.

Base-sledge moves the tissue block against a stationary microtome knife; Standard S.M. has a movable knife against a stationary tissue block.

Question 7

What are the types of sliding microtomes?

Answer 7

Base-sledge S.M. and Standard S.M.

Question 8

What is a disadvantage of the rocking microtome?

Answer 8

Difficulty in rotating the block.

NOT RECOMMENDED FOR HISTOPATH LAB.

Question 9

What is a characteristic of the rotary microtome?

Answer 9

Heavier but more stable; generally automated or semiautomated.

Question 10

What is a risk associated with the standard sliding microtome?

Answer 10

More dangerous because of the movable exposed knife.

Question 11

What is the purpose of the Freezing microtome?

Answer 11

Used to cut undehydrated thin to semi-thin sections of fresh, frozen tissues.

Invented by QUECKETT in 1848, it is used in rapid diagnosis and is provided with CO2 supply for freezing.

Question 12

What is a Cryostat?

Answer 12

A cold microtome used for freezing tissue into a block holder for easier sectioning.

It cuts sections of 4 micrometers and is kept inside a cold chamber (-5° - 30°C; average = -20°C), freezing fresh tissue within 2-3 minutes.

Question 13

What is the function of an Ultrathin microtome?

Answer 13

Equipped with a glass or diamond knife, it cuts very thin sections (60-100 nm).

Semi-thin sections are 0.5 - 1 micrometer.

Question 14

What is a Vibratome?

Answer 14

An instrument used to cut thin slices of material, usually thicker than those cut in paraffin-embedded samples.

It uses a vibrating blade to cut through unfixed, unfrozen specimens, which are liable to disintegrate.

Question 15

What is the length of a Plane Concave knife?

Answer 15

25mm in length.

Less concave is for celloidin and more concave is for paraffin.

Question 16

What is the length and use of a Biconcave knife?

Answer 16

Longest is 120mm in length and is used for paraffin (rotary).

It is specifically for cutting paraffin embedded tissue.

Question 17

What is the length and purpose of a Plain Wedge knife?

Answer 17

100mm in length and used for frozen sections and hard sections (base sledge).

Question 18

What should be done after sectioning with a microtome?

Answer 18

All accumulated paraffin and small pieces of tissue must be brushed away with a soft brush.

This prevents interference with the cutting of tissue blocks.

Question 19

How should movable portions of the microtome be maintained?

Answer 19

They should be oiled thoroughly to prevent rusting.

Question 20

What is a safety measure when using a microtome?

Answer 20

Staff should not be distracted when using the microtome due to the risks of injury from sharp blades.

Non-slip flooring is preferable in the vicinity of microtomes.

Question 21

What should be used to pick up sections or wax fragments?

Answer 21

Use forceps or a brush instead of fingers.

Question 22

What should be done when cleaning the microtome?

Answer 22

Always remove the knife or blade before cleaning.

No fluid must enter the inside of the instrument during cleaning.

Question 23

How often should the microtome be inspected?

Answer 23

At least once a year by a qualified service technician.

Question 24

What should be done with the microtome when left unattended?

Answer 24

It should be removed from the microtome when the instrument is left unattended or when cleaning the instrument.

Question 25

What is the bevel angle?

Answer 25

The angle formed between the cutting edge and the cutting facets, typically 27-32 degrees.

Question 26

How is the bevel angle maintained?

Answer 26

By means of a slide on the back.

Question 27

What is the wedge angle?

Answer 27

The angle on the edge of a wedge knife, typically 15 degrees, causing maximum penetration of tissues and preventing distortion.

Question 28

What is the clearance angle?

Answer 28

The knife is inclined at 5-10 degrees, ensuring the cutting facet will not compress the block during cutting.

Question 29

What is the thickness of the cutting edge compared to the section being cut?

Answer 29

The cutting edge must be thinner than the section being cut, ideally 4mm thick without causing striations.

Question 30

What is a general principle in cutting?

Answer 30

Bending of a section is never advantageous in cutting; the correct knife angle should be set.

Question 31

What does honing involve?

Answer 31

The removal of gross nicks on the knife edge using a hone that is 8" by 3".

Question 32

What is the direction for honing strokes?

Answer 32

"Heel to toe" direction with 20-40 double strokes.

Question 33

What types of honing stones are used?

Answer 33

Belgium Yellow/black for metal sharpening, Arkansas for polishing, and Carborundum for badly nicked knives.

Question 34

What is the purpose of stropping?

Answer 34

Final polishing that removes burrs and sharpens the cutting edge.

Question 35

What is the direction for stropping strokes?

Answer 35

"Toe to heel" with 40-120 double strokes.

Question 36

What are clean slides typically preferred for?

Answer 36

6 x 25 mm slides that are 1.0 -1.2 mm thick.

Question 37

What is the final test for sharpness of a microtome knife?

Answer 37

Von Mohl's Criterion, which indicates a slight reflection and a perfect straight line.

Question 38

What are disposable blades used for?

Answer 38

They can cut 2-4 micrometer thick sections with ease and are cheaper.

Question 39

What are glass knives used for?

Answer 39

Generally used for sectioning in microscopy, made from 40 x 2.5 cm plate glass strips.

Question 40

How should glass knives be cleaned?

Answer 40

Washed with detergent, rinsed with distilled water and alcohol, and dried with lint-free paper.

Question 41

What are diamond knives used for?

Answer 41

Used to cut any type of resin block for electron microscopy, already mounted in a metal block.

Question 42

What is the purpose of a water bath?

Answer 42

To allow the melting point of the paraffin wax.

Question 43

What is the recommended drying temperature for brain tissues?

Answer 43

A lower drying temperature of 37°C for 24 hours is used to avoid splitting and cracking due to excessive heat.

Question 44

What are forceps used for?

Answer 44

For handling sections during suction and for 'floating out' in a water bath.