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Histology > Fixatives (Wk 16, 17) > Flashcards

Fixatives (Wk 16, 17) Flashcards

1
Q

This does not affect spores and therefore tissue may still be infectious.

A

MICROWAVE

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2
Q

Air drying of smears can lead to what 4 problems

A
  • Enlarged cells and nuclei
  • Indistinct cell boundaries
  • Pale chromatin staining
  • Overall pale staining
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3
Q

A less toxic alternative to mercury.

A

ZINC SULFATE

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4
Q

What is a coating fixative and its purpose

A

Wax coating that protects cells during transport or until they can be stained

Prevents air-dry effect

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5
Q

Glutaraldehyde is usually used as a _% solution

A

2%

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6
Q

This causes proteins to swell.

A

ACETIC ACID

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7
Q

Main effect of formalin on staining?

A

Decreased amino (+) groups

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8
Q

Zinc sulphate fixation mechanism

A

Binds to histidine and cysteine residues to stabilize conformation of proteins

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9
Q

Fixative that precipitates proteins without denaturing them

A

acetone

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10
Q

Formalin is added to this fixative before use

A

B5

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11
Q

Routine use of B5

A

Bone marrow

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12
Q

General category of fixatives which cause proteins to precipitate.

A

COAGULANT

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13
Q

What is the working concentration of formalin

A

Max conc. of formaldehyde in solution = 40%

Diluted 1 in 10

Therefore, 10% neutral buffered formalin = 4% formaldehyde

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14
Q

What are the 2 reactions that occur during fixation with formalin

A
  1. Hemiacetal formation

2. Methylene bridge formation

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15
Q

Transport media for short term (~1 hr) storage

A

Place on saline moistened gauze in sealed container on ice

Refrigeration

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16
Q

Routine use of Zenker’s

A

Bone marrow

Lmyph nodes

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17
Q

How to make formalin from paraformaldehyde

A

Dissolve in water; faster in neutral pH

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18
Q

What is the primary purpose of a microanatomical fixative?

A

preservation of cellular and non-cellular structural elements

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19
Q

2 cons of Bouin’s

A
  • Excessive hardening

- Removes calcium and iron

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20
Q

These are formed when formaldehyde crosslinks proteins.

A

METHYLENE BRIDGES

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21
Q

This reaction is used to demonstrate the adrenal medulla and tumours of it

A

Chromaffin reaction

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22
Q

Typical fixatives for fluids

A

Ethanol
Saline in sterile container
Refrigeration

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23
Q

4 common ingredients in Zenker’s

A
  • Mercuric chloride
  • Potassium dichromate
  • Sodium sulphate
  • Water
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24
Q

Volume of fixative that should be used?

A

15-20x greater than tissue

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25
Q

Term for nuclear shrinkage and increased basophilia.

A

PYKNOSIS

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26
Q

Formalin solutions mainly reacts with this functional group.

A

AMINO GROUPS

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27
Q

2 main routine uses of osmium tetroxide fixative

A
  • Electron microscopy (as a fixative)

- Lipid stain (as a stain)

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28
Q

2 major aldehyde fixatives

A
  • Formalin

- Glutaraldehyde

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29
Q

2 main glutaraldehyde differences compared to formalin

A
  • Larger

- 2 aldehyde functional groups rather than 1

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30
Q

2 reactions involved in formalin fixation

A

1 - hemiacetal formation

2 - methylene bridge formation

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31
Q

Transport media for long term storage

A

Michel’s transport media

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32
Q

How to recognize and remove formalin pigment?

A

Found in bloody areas => brown

Remove w/ alcoholic picric acid

33
Q

Define methylene hydrate and what it’s also known as

A

The form of formaldehyde in aqueous solution

AKA methylene glycol

34
Q

What is paraformaldehyde

A

White precipitate of formalin that forms spontaneously

35
Q

3 common ingredients in Bouins

A
  • Picric acid
  • Formalin
  • Acetic acid
36
Q

Fixative that precipitates nucleic acids

A

acetic acid

37
Q

Fixative that is appropriate for in situ hybridization b/c it inactivates RNases

38
Q

This fixative makes lipids black.

A

OSMIUM TETROXIDE

39
Q

Routine use of Bouin’s

A

Trichrome post-fix

Testicular biopsies

40
Q

2 fixatives that contain mercury

A

Zenker’s (Helly’s)

B5

41
Q

What causes the formation of formalin pigment

A

Oxidation of formalin to formic acid (during storage) = lowers pH of solution

Causes hgb to break down to hematein

42
Q

Fixative of choice for hematopoietic tissues.

43
Q

What is karyolysis

A

Nuclear chromatin fades or dissolves

44
Q

Fixative useful in trichrome stain due to low pH (that’s not Bouins)

A

Picric acid

45
Q

The fixative which is also a commonly used dye is?

A

PICRIC ACID

46
Q

Best fixative for antigen preservation

A

Zinc/alcohol

47
Q

Typical fixatives for cell blocks

48
Q

Bouin’s removes these 2 minerals

A

Calcium and iron

49
Q

This fixative may result in free aldehydes.

A

GLUTARALDEHYDE

50
Q

Effect of formalin fixation on eosin staining and why

A

Decreases eosin staining

  • hemiacetal and methylene bridge formation requires amino groups = used up = fewer sites for eosin to bind to
  • net increase in negative charges
51
Q

How to neutralize osmium tetroxide

A

Large quantities of vegetable oil or sodium sulfite

52
Q

This is used mainly to fix cytology smears.

53
Q

4 advantages of making formalin from paraformaldehyde

A
  • Very pure formalin
  • Doesn’t easily re-polymerize
  • Methanol not required to prevent paraformaldehyde formation
  • Doesn’t usually form formic acid
54
Q

Typical fixatives for smears

A

Ethanol
Ethanol/acetic acid
Air dry
Coating fixatives

55
Q

Best for fixative for hematology specimens

56
Q

4 common ingredients in B5

A
  • Mercuric chloride
  • Sodium acetate
  • Water
  • Formalin (add immediately before use)
57
Q

Another word for polymerized formaldehyde

A

Paraformaldehyde

58
Q

The one fixative that causes proteins to swell

A

Acetic acid

59
Q

When used like this alcohol works well for enzyme Histochemistry.

60
Q

The presence of this may lead to an artifact pigment which can be removed by alcoholic picric acid.

A

FORMIC ACID

61
Q

Used to demonstrate adrenal medulla and tumors of it

A

Chromaffin reaction (dichromate fixative)

62
Q

What is karyorrhexis

A

Fragmentation of nuclei

63
Q

Main ingredients of this fixative: picric acid, formalin and acetic acid.

64
Q

Fixation mechanism behind chromates

A

Attaches to phospholipids and renders them insoluble

65
Q

This is added to prevent polymerization of formaldehyde.

66
Q

Common ingredient in combination fixatives like Zenker’s

A

Potassium dichromate

67
Q

4 cons of Zenker’s

A
  • Toxic (mercury)
  • Hardening of tissues
  • Nonspecific silver precipitaes
  • Mercury artifacts
68
Q

Difference between Zenker’s and Helly’s

A

Helly’s - add formalin instead of acetic acid

69
Q

Effect of glutaraldehyde fixation on PAS stain

A

False positives due to glutaraldehyde containing aldehyde groups

70
Q

Fixative that may be used for frozen sections for enzyme histochemical rxns

71
Q

Chromates fixation mechanism

A

Attaches to phospholipids and renders them insoluble

72
Q

Mercury fixation mechanism

A

Affects SH (thiol) groups of proteins

73
Q

How to neutralize glutaraldehyde

A

Sodium bisulfite or sodium hydroxide

74
Q

Which chemical may be used as a substitute for mercuric chloride in a fixative?

A

Zinc sulphate

75
Q

Fixative that enhances nuclear staining

76
Q

Main routine use of glutaraldehyde fixative?

A

Electron microscopy

77
Q

General fixative volume to tissue ratio

78
Q

Difference between formaldehyde and formalin

A

Formaldehyde = gas

Formalin = aqueous saturated solution of formaldehyde

Histology (18 decks)

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