CHAPTER 9: DEHYDRATION

Process of removing intracellular and extracellular water from tissue following decalcification and prior to wax impregnation.

Dehydration

An ideal dehydrating solution should?

Dehydrate rapidly without producing considerable shrinkage or distortion to tissues.

Most commonly used dehydrating agent

Alcohol

Best dehydrating agent

Ethyl Alcohol

Successive changes of increasing concentration for routine tissue dehydration

70%-95%-100%

Successive changes of increasing concentration for delicate tissue

30%-40%-50%

Used for blood films and smear preparations

Methyl Alcohol

Used for plant and animal micro-technique

Butyl Alcohol

Used as an indicator for complete dehydration

Anhydrous Copper Sulfate

Advantage: Miscible in all proportions with water. Can be used on eyes and embryos, if graded alcohols are used.

Disadvantage: Long periods can cause excessive shrinkage and hardening. Extracts methylene blue and other thiazine dyes from sections. Extracts more lipids than acetone. May react with an unreduced 0s04 remaining in specimen.

Ethyl Alcohol

Advantages: Less shrinkage and hardening, excellent for slow processing, miscible with paraffin.

Disadvantages: Odorous, slow-acting, dehydrating power is low

Butyl Alcohol

Advantages: Universal solvent, acts as dehydrating and clearing agent, mixes with water, ethanol, xylene, and paraffin.

Disadvantages: Odorous, more expensive than butanol, primary infiltration must be done in half tertiary butanol and half paraffin, prior to paraffin impregnation. Reagent tends to solidify at room temperature or below 25C

Tertiary Butanol (Butyl Alcohol)

Excellent substitute for ethanol, Lillie considers it "the best all- around substitute for ethyl alcohol"

Isopropanol (Isopropyl Alcohol)

- Cannot be used in the celloidin technique since nitrocellulose is insoluble in it

- Cannot be used for preparing staining solutions, since dyes are not soluble in it

Isopropanol (Isopropyl Alcohol)

- Miscible with 90% alcohol, toluene and xylene

- Dissolves paraffin wax

Pentanol (Amyl Alcohol)

- Toxic

- Cannot be used in poorly ventilated rooms

- Not miscible with water

Pentanol (Amyl Alcohol)

Used for urgent biopsies

Acetone

How long does acetone take to dehydrate

1/2 - 2 hours

Rapid in action but penetrates tissues poorly & may cause brittleness in tissues when tissues are placed in prolonged period of time.

Acetone

- Excellent dehydrating and clearing agent

- Miscible with both water and paraffin

- Tissue ribbons dehydrated with dioxane tends to ribbon poorly

Dioxane

Advantages: rapid dehydrating agent, Does not extract methylene blue and other dyes from stained sections, cause less shrinkage, not reactive with 0s04 remaining in the specimen.

Disadvantages: requires a clearing agent, volume must be 20 times that of the tissue, Flammable, only soluble in uranyl acetate and phosphotungstic acid.

Acetone

Advantages: Universal solvent, it dehydrates and clears

Miscible with water, alcohol, xylene, and paraffin, Does not harm tissue over long time periods, Faster dehydrant than ethanol.

Disadvantages:

- Needs large volume for dehydration

- Costs about for times more than does absolute alcohol

- Must be used in well-ventilated rooms

- Cumulatively toxic

- Odorous

- Distorts tissue-containing cavities

Dioxane

Dehydrates rapidly and does not cause hardening or distortion in tissues.

Cellosolve (ethylene glycol monoethyl ether)

Rapid dehydrating agent

Tissue may remain in it for months without injury

Avoids distortion and does not require graded dilutions

Cellosolve

Disadvantages:

Expensive

Rapidly absorbs water from the air

Requires clearing agent

cellosolve

Used to dehydrate sections and smears following certain procedures minimum shrinkage.

Triethyl Phosphate

Advantages:

- May be used in routine paraffin technic

- Displaces water readily with slight distortion

- May be used as a dehydrating solution in the staining sequence

- Soluble in alcohols, benzene, toluene, xylene, ether, chloroform

Triethyl phosphate

Dehydrates and clears tissue, miscible with water and paraffin.

Tetrohydrofuran (THF)

Miscible in all proportions with water, ether, chloroform, acetone, and the hydrocarbons xylene, toluene, and benzene

Rapid without excessive shrinkage and hardening Low toxicity; low fire and explosion hazard

Has better results than most universal solvents

Solvents of mounting media

tetrahydrofuran (THF)

Disadvantages:

Odorous, should be used in well-ventilated room

Evaporates rapidly

Dyes are not soluble

Tetrahydrofuran (THF)