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Histology Fall 2019 > Processing > Flashcards

Flashcards in Processing Deck (42):
1

incomplete dehydration

accounts for the vast majority of processing problems and results in mushy tissue

2

alcohols

the most common dehydrating reagents

3

clearing agents

must be miscible with both the dehydration agent and the infiltration medium
primary purpose is to remove the alcohol used to dehydrate the tissue

4

prolonged clearing

results in hard, brittle tissues

5

xylene

most commonly used clearing agent, turns cloudy in the presence of water

6

toluene

does not over harden tissue as much as xylene

7

overdehydration

seen as microchatter in H&E stained slides, commonly seen in biopsy specimens, can be corrected by processing biopsies separately from other tissues and decreasing the amount of time in the dehydrating solutions

8

poor processing

evidenced by poor nuclear staining, often caused by water remaining in the tissue when it is placed in the clearing agent which results in poor clearing and infiltration, can also be caused by too much heat during processing

9

melting point

high melting point results in hard blocks that section thinly but ribbon poorly, while low melting point ribbons easily but doesn't section as thin. 55-58C is common melting point

10

diagonal embedding

makes sectioning much easier

11

forceps metastasis

when fragments of tissue are transferred between blocks if the forceps aren't wiped down between specimens

12

paraffin crystal size

smaller is better, allows for better support of the tissue

13

mushy in the middle

tissue was cut too thick during grossing and needs to be reprocessed

14

dehydrant

alcohol for removal of water

15

clearing agent

xylene to remove the alcohol and make the tissue receptive to paraffin, high index of refraction renders tissue transparent

16

infiltrating medium

paraffin infiltrates the tissue and gives it support

17

open tissue processor

rarely used because of reagent evaporation

18

closed tissue processor

preferred method

19

Ethanol (ethyl alcohol)

clear, colorless, flammable
fast, best dehydrant
hydrophilic
70-95-100% steps help reduce tissue shrinkage

20

Methanol (methyl alcohol)

clear, colorless, flammable, poisonous
rarely used
except for fixation of blood smears

21

Isopropanol (Isopropyl alcohol)

flammable, toxic
excellent substitute for ethanol
eosin can't stain with it
doesn't harden or shrink tissue as much as ethanol

22

Acetone

volatile, flammable
dehydrates rapidly, cheap
excessive shrinkage
absorbs water when exposed to air
hard to maintain solution levels in open air processors

23

xylene

most commonly used clearing agent
can overharden tissues
intolerant of water left in the tissue
flammable hazardous neurotoxin, do not pour down the sink

24

toluene

flammable, more volatile than xylene
does not overharden tissue as much as xylene

25

benzene

very volatile and toxic, carcinogen
fast acting, doesn't overharden as much as xylene but not used in histology

26

chloroform

volatile, carcinogen
makes tissue less brittle than xylene
clears tissue slowly
must use in tight containers because it easily absorbs water from the air
best for uterus muscle and tendon

27

cedarwood oil

volatile, strong odor
hardens and damages tissue the least out of any reagent
clears quickly
used for special projects

28

limonene

xylene substitute
harden tissues less than xylene but contaminates teh paraffin more often
can't dispose down drain

29

why is paraffin routinely used

large number of blocks can be processed in a short amount of time
easy to get serial sections as well as routine and special stains

30

water present during dehydration

results in mushy tissue and incomplete clearing and infiltration

31

how fixative pH affects the processing unit

if zinc formalin goes above pH 7 it can cause formation of precipitates

32

precautions for handling tissue processing reagents

gloves, most of the reagents are dangerous or irritants

33

importance of preventative maintenance on tissue processors

keep solutions clean so that there isn't carryover of water causing underprocessing, maintain temperatures to prevent overprocessing and hardening of tissue

34

why do we decalcify?

because calcium deposits damage the microtome blade and make sectioning very difficult

35

why do we carefully monitor decalcification?

because it is essential to make sure the specimen is neither overdecacified nor underdecalicied since either state results in undesirable staining outcomes; no nuclear staining or left over calcium that stains very darkly and can damage the blade

36

decalcification

occurs after fixation but before processing

37

pros and cons of acid decalcifiers

fast is both a pro and con, need to carefully monitor the process so the sample isn't over or underdecalcified

38

function of acid decalcifiers

acidic solutions between pH 3 and 5, calcium salts dissolve and then ionize, migrating into the surrounding solution. This is the most common type of decalcification in histology

39

determining the endpoint of decalcification

mechanical: test flexibility or scrape, no one does this method
chemical: the decalcifying solution is checked for the presence of calcium
radiography: x-rays are used to show that decalcification is complete

40

why do we remove decalcifying agents prior to processing?

to prevent carryover of acids that would interfere with processing

41

how to preform localized decalcification

once the block has been faced the surface can be placed in decal solution, then rinsed and sectioned to break down any calcium deposits that remain

42

Max size

2cm square, 3-4mm thick