P2: Microtomy Flashcards
The process by which processed tissue, most commonly a paraffinembedded tissue, is trimmed and cut into uniformly thin slices known as sections to facilitate studies under the microscope
Microtomy
Essential Parts of a Microtome
- Block Holder
- Knife carries and knife
- Pawl, ratchet feed wheel and adjustment screw
Where tissues are held in position
Block holder
For actual cutting of tissue sections
Knife carrier and knife
To line ip the tissue block with the knife, adjusting the thickness of the tissues
Pawl, ratchet feed wheel and adjustment screws
Types of Microtome
- Rocking
- Rotary
- Sliding
- Freezing
- Ultrathin
Used for cutting sections of large blocks of paraffin embedded tissues
Rocking Microtome
Rocking microtome is invented by _____
Paldwell Trefall in 1881
The simplest among the different types of microtomes
Rocking Microtome
Used for cutting sections embedded in paraffin
Rotary Microtome
Rotary Microtome was invented by
Minot in 1885-86
Most common type used in routine and research laboratories
Rotary Microtome
Used for celloidin embedded sections
Sliding Microtome
Sliding Microtome was invented by
Adams in 1979
Two types of Sliding Microtome
Base sledge
Standard sliding
Used for unembedded frozen sections
Freezing Microtome
Freezing microtome was invented by
Queckett in 1848
Useful in rapid diagnosis and sensitive tissue constituents that are damaged or destroyed by heat
Freezing Microtome
A refrigerated apparatus used in fresh tissue microtomy
Cryostat/Cold Microtome
Consists of a rotary microtome, kept in cold chamber
Cryostat / Cold Microtome
Cryostat is maintained at temperature:
-5 to -30C or (20C average)
Useful for rapid preparation of urgent tissue biopsies for intraoperative diagnosis
Cryostat / Cold Microtome
Used for cutting tissues in preparation for electron microscopy
Ultrathin Microtome
Specific size of Ultrathin Microtome
0.5 micra
Knife used in Ultrathin Microtome
Fragments of broken plate glass
Specimens in Ultrathin microtome must be:
Small, Fixed in Osmium Tetroxide; embedded in plastic
Microtome Knives:
plane concave
biconcave
plane wedge
Size of Plane Concave
25 mm
size of biconcave
120 mm
size of plane wedge
100 mm
One side flat; the other is concave
Plane concave
Both sides concave
Biconcave
Both sides are straight
Plane wedge
Microtome knife used in celloidin-embedded tissues
Plane concave
Microtome knife used in paraffin embedded tissues
Biconcave
Microtome knife used in Frozen Sections; Extremely hard specimens in paraffin
Plane wedge
If not corrected, it will produce tears and striae in tissue sections
Jagged edges
Involves the removal of gross nicks on the knife edges (coarse honing)
Honing
To remove blemishes, and grinding the cutting edge of the knife on a stone
Honing
The degree of sharpness is proportional to the fineness of the abrasive used in sharpening
Honing
Types of Hones
Belgium yellow
Arkansas
Fine Carborundum
For manual sharpening, for nicked and blunted cutting edges of knife
Belgium yellow
Gives more polishing effect than Belgium yellow
Arkansas
Much coarser, used for very badly nicked knives
Fine carborundum
Honing Procedure:
- Wipe the surface of the hone with a sift cloth moistened with xylene
- Cover the hone with mineral of clove oil or soapy water
- The knife is fitted and with its cutting edge first, the heel is drawn diagonally until the toe, head portion
- Again with step 3, edge first, with a direction
Process of removing the burrs formed during honing and the cutting edge of the knife is polished
Stropping
If the knee becomes blunt and dull, but is free from nicks or teeth, it is usually necessary to _____
stropping
Procedure of Stropping
- Use a paddle strop, with good quality horse leather
- Toe to heel direction, around 40-120 double strokes are usually required
Provide the Reason and Remedy for each fault:
Brittle or hard tissue
Reason: prolonged fixation, D, C, EM
Remedy: Soak tissue in bowl containing water with phenol
Provide the Reason and Remedy for each fault:
Clearing agent turns milky
Reason: Incomplete dehydration
Remedy: Repeat dehydration with absolute alcohol then clear again
Provide the Reason and Remedy for each fault:
On trimming wax appears crystalline
Reason: Contaminated wax
Remedy: Re-embed in freshly filtered wax
Provide the Reason and Remedy for each fault:
Frozen tissue chips into fragments when cut
Reason: Tissue is frozen too hard
Remedy: Warm the tissue with the fingers