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histupar lab > DEHYDRATION > Flashcards

DEHYDRATION Flashcards

1
Q

What are the main steps involved in tissue processing?

A

Dehydration

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2
Q

What is the purpose of dehydration in tissue processing?

A

Removal of water from aqueous-fixed tissue.

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3
Q

Why is clearing necessary after dehydration?

A

Because most alcohols and paraffin are not miscible.

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4
Q

List the steps in tissue processing in order.

A
  1. Numbering
  2. Fixation
  3. Decalcification
  4. Dehydration
  5. Clearing
  6. Impregnation
  7. Embedding
  8. Blocking
  9. Trimming
  10. Sectioning
  11. Staining
  12. Mounting
  13. Labelling
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5
Q

What is the pre-eminent method of tissue processing for routine preparation?

A

Paraffin Wax method.

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6
Q

Why is the Paraffin Wax method preferred for routine tissue processing?

A

It is suitable for routine preparation

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7
Q

What does the Paraffin Wax method utilize as dehydrating fluid?

A

A series of alcohols.

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8
Q

Name the characteristics of an ideal dehydrating solution.

A
  1. Rapid dehydration without significant shrinkage
  2. slow evaporation
  3. ability to dehydrate fatty tissues,
  4. minimal hardening
  5. does not remove stains
  6. non-toxic,
  7. not a fire hazard.
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9
Q

List commonly used dehydrating agents.

A
  1. Alcohol (most common)
  2. Acetone
  3. Dioxane
  4. Cellosolve
  5. Triethyl phosphate
  6. Tetrahydrofuran
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10
Q

Which alcohol is recommended for routine dehydration of tissues and why?

A

Ethyl alcohol (ethanol) because:
- it is fast-acting
- mixes well with water and inorganic solvents
- penetrates tissues easily
- not poisonous
- not expensive

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11
Q

What is a disadvantage of using methyl alcohol (methanol) as a dehydrating agent?

A

It is toxic to the body.

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12
Q

Why is butyl alcohol (butanol) not suitable for rapid tissue processing?

A

Because it is a slow dehydrating agent.

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13
Q

Describe the dehydration process in tissue processing.

A

Removal of water from tissue using dehydrating agents, often a series of increasing alcohol concentrations to prevent tissue distortion.

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14
Q

What is the role of anhydrous copper sulfate in alcohol dehydration?

A

It serves as an indicator to ensure the final alcohol bath is free of water by turning blue if alcohol gets diluted.

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15
Q

What are the advantages of using acetone as a dehydrating agent?

A
  • Cheap
  • rapid-acting
  • more miscible with epoxy resins than alcohol.
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16
Q

What are the disadvantages of using acetone?

A
  • Highly flammable
  • penetrates tissues poorly
  • causes brittleness
  • removes most lipids
  • extremely volatile.
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17
Q

What is dioxane used for in tissue processing?

A

As a dehydrating and clearing agent.

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18
Q

List the advantages of using dioxane.

A
  • Produces less tissue shrinkage
  • , tissues can be left in it for long periods without affecting consistency or staining
  • can be placed directly after washing.
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19
Q

List the disadvantages of using dioxane.

A
  • Expensive
  • extremely dangerous
  • poor ribboning of tissue sections
  • highly toxic vapors
  • increases risk of explosive peroxides.
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20
Q

What is Graupner’s Method in dioxane dehydration?

A

A time schedule involving multiple pure dioxane solutions followed by paraffin wax infiltration and embedding.

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21
Q

What is Weiseberg’s Method?

A

Tissues are wrapped in gauze and dehydrated in a bottle containing dioxane and anhydrous calcium oxide

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22
Q

What is Cellosolve and its primary use in tissue processing?

A

Ethylene glycol monoethyl ether used as a rapid dehydrating agent that does not harden or distort tissues.

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23
Q

What precautions should be taken when using Cellosolve?

A

It is combustible at 110-120°F and toxic; use propylene-based glycol ether if possible.

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24
Q

What is triethyl phosphate used for in tissue processing?

A

Removes water readily with minimal distortion and hardening

25
Q

What is tetrahydrofuran (THF) used for?

A

Both dehydrates and clears tissues

26
Q

What are the disadvantages of using tetrahydrofuran (THF)?

A

It is toxic

27
Q

How does the dehydration schedule vary based on the fixative used?

A

Different fixatives require different alcohol concentrations and exposure times to prevent tissue shrinkage and ensure proper dehydration.

28
Q

What is the typical dehydration sequence for specimens not more than 4mm thick?

A

70% ethanol for 15 min

29
Q

Why is the strength of initial alcohol concentration important in dehydration?

A

It depends on tissue size and nature; smaller

30
Q

What happens if tissues are stored in concentrated alcohols for too long?

A

They produce shrinkage and make the tissue hard

31
Q

What is the effect of prolonged storage in lower concentrations of alcohol (below 70%)?

A

It tends to macerate the tissue.

32
Q

How does temperature affect the dehydration process?

A

Higher temperatures

33
Q

What indicates that the final alcohol bath is free of water during quality check?

A

Anhydrous copper sulfate turns blue if alcohol is diluted with water.

34
Q

What is the main purpose of fixation in tissue processing?

A

To preserve the tissue by using aqueous fixatives.

35
Q

What concentration of ethanol is typically used during fixation in the Paraffin Wax method?

A

60-70% ethanol.

36
Q

How many changes of absolute alcohol are used in the Paraffin Wax method clearing step?

A

2-3 changes.

37
Q

What factors influence the strength of initial alcohol required in dehydration?

A

Size and nature of the tissue and the type of fixative used.

38
Q

Why should tissues treated with chromate fixatives be washed before using dioxane?

A

To remove chromate

39
Q

What is the advantage of using Cellosolve over other dehydrating agents?

A

It dehydrates rapidly and can be stored without causing hardening or distortion.

40
Q

What safety precautions are necessary when handling dioxane?

A

Proper ventilation

41
Q

What does embedding involve in tissue processing?

A

Encasing the dehydrated tissue in a solid medium like paraffin wax to allow for thin sectioning.

42
Q

What is the purpose of sectioning in tissue processing?

A

To cut the embedded tissue into thin slices for microscopic examination.

43
Q

Why is mounting important in preparing tissue sections for microscopy?

A

It secures the tissue sections onto slides and preserves them for staining and viewing.

44
Q

What should be done if tissues do not penetrate deeply during dehydration?

A

Use lower concentrations of alcohol and shorter intervals between steps.

45
Q

What is the consequence of unequal impregnation in tissue processing?

A

Poor sectioning and inconsistent staining.

46
Q

How does the Paraffin Wax method aid in the storage of tissue samples?

A

Allows for long-term storage without significant degradation.

47
Q

What is the role of impregnation in tissue processing?

A

To infuse the tissue with wax or another embedding medium after clearing.

48
Q

What happens during the clearing step in tissue processing?

A

Removal of alcohol and other dehydrants

49
Q

Why should dioxane not be used routinely despite its advantages?

A

Due to its high cost

50
Q

What is the effect of concentrated alcohol on tissue during dehydration?

A

It causes tissue shrinkage

51
Q

Which dehydrating agent is considered the best for routine dehydration and why?

A

Ethyl alcohol (ethanol) because of its effectiveness and safety profile.

52
Q

What is the main disadvantage of using butyl alcohol in dehydration?

A

Its slow action makes it unsuitable for rapid processing.

53
Q

What property of tetrahydrofuran (THF) improves staining procedures?

A

It dissolves many substances and clears tissues effectively.

54
Q

How does triethyl phosphate contribute to minimal tissue shrinkage?

A

It removes water readily with very little distortion and hardening.

55
Q

What should be used instead of ethylene-based glycol ethers if they cannot be avoided?

A

Propylene-based glycol ethers.

56
Q

What is the advantage of using a graded alcohol series in dehydration?

A

Prevents tissue shrinkage and distortion by gradually removing water.

57
Q

What is the purpose of blocking in tissue processing?

A

To organize the embedded tissue into a manageable shape for trimming and sectioning.

58
Q

What happens during trimming in tissue processing?

A

Excess embedding medium is removed to expose the tissue for sectioning.

59
Q

Why is labeling important in the final steps of tissue processing?

A

To identify and organize tissue samples for future reference and study.

histupar lab (18 decks)

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