DEHYDRATION Flashcards
Percent and Time
70 - 15mins
90 - 15mins
95 - 30mins
100 - 30mins
100 - 45mins
removal of water before infiltration
Dehydration
melted paraffin wax is_______
(mao na need i dehydrate)
hydrophobic
Dehydration
Immersing the specimen in a series of
increasing concentrations of alcohol
The most common manner of carrying it out is by immersing specimens in a series of_______ solutions of increasing concentration until pure, water-free alcohol is reached.
ethanol (alcohol)
is miscible with water in all proportions so that the water in the specimen is progressively replaced by the it
Ethanol
A series of increasing concentrations is used to avoid…
excessive distortion of the tissue
As a general rule, it is relevant to keep contact time with chemicals as brief as possible to limit_______ and to minimize the_________
tissue distortion
risk of extracting cellular constituents
The ideal amount of dehydrating agent, whatever type it may be, should also be maintained at a fluid to tissue ratio of_____ to achieve adequate dehydration
10:1
Dehydrating agent CHARACTERISTICS
a. Dehydrate rapidly without producing considerable tissue shrinkage;
b. Not evaporate too fast;
c. Not harden tissues excessively;
d. Not remove stains;
e. Not be a fire hazard;
f. Not be toxic to the handler (e.g. histotechnologist);
g. Be able to dehydrate a wide range of tissue types.
Dehydrating Agents
• Alcohols
• Glycol-Ethers
• Acetone
• Tetrahydrofuran
Alcohols
- Ethanol
- Methanol
- Isopropanol
Glycol-Ethers
- 2-ethoxyethanol / ethylene glycol monoethyl ether (cellosolve)
- Dioxane
- Polyethylene glycols
- clear, colorless, flammable, hydrophilic liquid
- miscible with water
- when anhydrous, miscible with most organic solvents
Alcohols
Alcohols
also acts as…
secondary coagulant fixatives
Examples of alcohol
Ethanol
Methanol
Isopropanol
is probably the most commonly used dehydrating agent in histology.
Ethanol
It is a rapid, efficient and widely applicable agent.
Ethanol
It is normally a poor lipid solvent except under microwave processing conditions.
Ethanol
It dissolves nitrocellulose slowly unless combined in equal proportions 1:1 (or better, 1:2) with diethyl ether
Ethanol
Processing times in absolute ethanol should be minimal.
Minimal processing time
Ethanol
Progressive removal of bound water from carbohydrates and proteins during prolonged immersion in absolute ethanol causes tissues to harden excessively and become brittle.
Ethanol
Colloid, blood, collagen and yolky tissues are particularly affected. The problem is exacerbated by heat during wax infiltration.
Ethanol
is a good ethanol substitute but rarely used for routine processing because of its volatility, flammability and cost
Methanol
• poor lipid solvent
• does not dissolve nitrocellulose (unless mixed with acetone)
Mathanol
In microwave processing it tends to harden tissues more than ethanol.
Methanol
Ethanol
It dissolves nitrocellulose slowly unless combined in equal proportions (or better, 1:2) with______
diethyl ether
Methanol
It is a poor lipid solvent, and will not dissolve nitrocellulose unless mixed with______.
acetone
was first suggested as an ethanol substitute during the prohibition era in the United States.
Isopropanol
It is a universal solvent
Isopropanol
slightly slower in action and not as hydroscopic as ethanol
Isopropanol
a far superior lipid solvent
Isopropanol
• completely miscible with water and most organic solvents
• fully miscible with melted paraffin wax
• readily expelled from tissues and water baths
Isopropanol
It shrinks and hardens tissues less than ethanol and is used to dehydrate hard, dense tissues, which can remain in the solvent for extended periods without harm.
Isopropanol
To minimize shrinkage, fixed tissues are transferred via 60%-70% isopropanol or ethanol to absolute isopropanol.
Isopropanol
is a solvent for some lipid-soluble dyes, but is not used in staining work stations as many other dyes are insoluble in this solvent.
Isopropanol
Unlike the alcohols, these reagents do not act as secondary fixatives, and apart from solvent effects do not appear to alter tissue reactivity
GLYCOL-ETHERS
is a colorless flammable liquid with sharp characteristic ketonic odor, low toxicity and is freely miscible with water and organic solvents
ACETONE
is a colorless, highly volatile and flammable universal solvent with an offensive ethereal odor.
TETRAHYDROFURAN
What makes ethanol the most common choice for a dehydrating agent?
Ethanol is miscible with water in all proportions so that the water in the specimen is progressively replaced by the alcohol. A series of increasing concentrations is used to avoid excessive distortion of the tissue.
What is the purpose of subjecting formalin-fixed tissues to an ascending order of graded alcohol?
The graded series of alcohols ensures that the tissue is not extremely distorted due to the constant use of the alcohol.
