3.2-DEHYDRATION AND CLEARING

Question 2

What process displaces residual fixatives and cellular water (free water) from tissues?

Answer 2

Dehydration

Question 3

What is the purpose of graded alcohols in dehydration?

Answer 3

To remove free water while keeping bound water intact

Question 4

What artifacts result from overprocessing during dehydration?

Answer 4

Shrinkage+parched earth effect+abnormal staining+dry brittle tissues during microtomy

Question 5

What happens if dehydration is incomplete?

Answer 5

Impaired penetration of clearing reagents+tissue remains soft and non-receptive to paraffin wax infiltration

Question 6

What are the two forms of water in tissues?

Answer 6

Bound water (integral to macromolecules)+Free water (removed during dehydration)

Question 7

What is removed during dehydration to stabilize tissues for paraffin wax infiltration?

Answer 7

Free water

Question 8

What happens if bound water is removed during excessive dehydration?

Answer 8

Overprocessing artifacts such as shrinkage and distortion

Question 9

What process removes all water from tissues?

Answer 9

Drying

Question 10

What characteristics define an ideal dehydrating solution?

Answer 10

Rapid dehydration without shrinkage+non-toxic+non-flammable+effective on fatty tissues+does not harden excessively or remove stains

Question 11

What sequence of alcohol concentrations is used in the dehydration process?

Answer 11

70% ethanol→90% ethanol→100% ethanol (repeated)

Question 12

What is the most commonly used dehydrating agent?

Answer 12

Ethanol

Question 13

Why is ethanol considered the best dehydrating agent?

Answer 13

Fast-acting+nontoxic+miscible with water+causes less extraction of cellular components+inexpensive and easily obtained

Question 14

What dehydrating agent is toxic and primarily used for blood smears rather than tissue processing?

Answer 14

Methyl alcohol

Question 15

What dehydrating agent is slow-acting and used in plant/animal micro-techniques?

Answer 15

Tertiary butanol (butyl alcohol)

Question 16

What are the advantages of butanol as a dehydrating agent?

Answer 16

Less shrinkage and hardening+miscible with paraffin+excellent for slow processing

Question 17

What are the disadvantages of butanol?

Answer 17

Odorous+slow-acting+long infiltration periods required+low dehydrating power

Question 18

What universal solvent acts as both a dehydrating and clearing agent?

Answer 18

Tertiary butanol (butyl alcohol)

Question 19

Why is tertiary butanol not ideal despite its versatility?

Answer 19

Expensive+tends to solidify below 25°C+requires primary infiltration with half tertiary butanol/half paraffin before impregnation

Question 20

What dehydrating agent is an excellent substitute for ethanol with less shrinkage and hardening?

Answer 20

Isopropanol (boiling point: 82.3°C)

Question 21

Why can’t isopropanol be used in celloidin techniques or staining solutions?

Answer 21

Nitrocellulose is insoluble+dyes are not soluble in it

Question 22

What dehydrating agent dissolves paraffin wax but cannot be used in poorly ventilated rooms due to toxicity?

Answer 22

Pentanol (boiling point: 128°C)

Question 23

What rapid-acting dehydrating agent penetrates poorly

Answer 23

dissolves lipids

Question 24

What are the advantages of acetone as a dehydrating agent?

Answer 24

Rapid action+miscible with embedding resins+less expensive than ethanol alternatives

Question 25

Why is acetone not ideal for routine use?

Answer 25

Highly volatile+causes tissue shrinkage and brittleness+dissolves lipids excessively compared to ethanol

Question 26

Which rapid dehydrating agents avoid distortion and graded dilutions but require clearing agents?

Answer 26

Dioxane and Cellosolve (ethylene glycol ethers)

Question 27

Why are dioxane and cellosolve rarely used despite their efficiency?

Answer 27

Expensive+toxic by inhalation/skin contact/ingestion+combustible at 110-120°F+absorb water rapidly from air

Question 28

Which dehydrating agent displaces water readily without excessive distortion or hardening?

Answer 28

Triethyl phosphate (boiling point: 215°C)

Question 29

Why is triethyl phosphate considered versatile for routine paraffin techniques and staining sequences?

Answer 29

Miscible with alcohols

Question 30

What is the process of removing alcohol or a dehydrating agent from tissues and replacing it with a substance that dissolves wax or serves as a mounting medium?

Answer 30

Clearing

Question 31

What are the characteristics of an ideal clearing agent?

Answer 31

Miscible with alcohol+miscible with paraffin wax or mounting medium+does not cause shrinkage

Question 32

What is the most widely used clearing agent for both embedding and mounting?

Answer 32

Xylene

Question 33

What are the advantages of xylene as a clearing agent?

Answer 33

Rapid action+makes tissue transparent+miscible with absolute alcohol and paraffin+does not extract aniline dyes+does not dissolve celloidin

Question 34

What are the disadvantages of xylene?

Answer 34

Highly inflammable+toxic+causes considerable hardening and shrinkage+excessively hard and brittle tissue+evaporates quickly

Question 35

What clearing agent is slower than xylene but prevents tissues from becoming excessively hard and brittle?

Answer 35

Toluene

Question 36

What are the disadvantages of toluene?

Answer 36

Tends to acidify+toxic+expensive

Question 37

What clearing agent is rapid-acting with minimal shrinkage but is highly flammable and carcinogenic?

Answer 37

Benzene

Question 38

Why is benzene rarely used despite its rapid action?

Answer 38

Toxicity and carcinogenic properties

Question 39

What clearing agent is recommended for tough tissues like skin

Answer 39

fibroids

Question 40

What are the disadvantages of chloroform as a clearing agent?

Answer 40

Toxicity+carcinogenic properties+slower action+tissues tend to float+does not make tissues transparent

Question 41

What clearing agent is recommended for CNS tissues

Answer 41

smooth muscles

Question 42

What are the disadvantages of cedarwood oil?

Answer 42

Hard to eliminate from tissues in paraffin bath+quality may vary+extremely slow action

Question 43

What plant-derived clearing agents render tissues transparent with a slow

Answer 43

gentle non-hardening action?

Question 44

What citrus-based volatile oil clearing agent has low hazard but may irritate skin and does not mix well with mounting media?

Answer 44

D-limonene (e.g.

Question 45

What aliphatic hydrocarbon clearing agents are non-sensitizing

Answer 45

non-irritating

Question 46

What natural oil serves as an efficient xylene substitute but tends to solidify at lower temperatures?

Answer 46

Coconut oil