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Histopathology > Fixation > Flashcards

Fixation Flashcards

1
Q

First and most critical step

A

Fixation

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2
Q

Primary aim

A

To preserve in life-like manner

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3
Q

Secondary goal

A

To harden and protect

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4
Q

The most important reaction

A

Stabilization of proteins

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5
Q

Stabilization of proteins can be achieved by

A

Forming cross-links between proteins

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6
Q

Fixes tissues by forming cross-linkage between lysine residues

A

Formaldehyde

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7
Q

Fixative is taken in, becomes part of the tissue through cross-links

A

Additive

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8
Q

Fixative is not incorporated but alters tissue composition and stabilizes it through water removal

A

Non-additive

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9
Q

pH in fixation

A

6.0-8.0

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10
Q

pH of normal phosphate buffered saline-based fixative

A

7.0

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11
Q

Usual temp

A

RT (18-30degC)

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12
Q

Tissue processor temp

A

40-42degC

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13
Q

EM and histochem temp

A

0-4degC

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14
Q

Mast cells for EM temp

A

RT

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15
Q

Slows down decomposition if tissue cannot be fixed immediately

A

Refrigeration

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16
Q

Rapid dixation of urgent biopsy specimen

A

Formalin heated to 60degC

17
Q

Fix tissues with tuberculosis

A

Formalin heated to 100degC

18
Q

Thicknes of sections for EM

A

1-2 mm^2

19
Q

Thicknes of sections for light microscopy

A

2 cm^2

20
Q

Thicknes of sections for thin LM

A

0.4 cm or 4 mm

21
Q

Large solid tissues like uterus should be

A

Opened/sliced thinly

22
Q

Brain is usually suspended in ___ for ___

A

10% NBF; 2-3 weeks

23
Q

Osmolality for best results are obtained using

A

Slightly hypertonic (400-450 mOsm)

24
Q

Added to osmium tetroxide fixatives for EM

A

Sucrose

25
Q

Formaldehyde concentration

A

10%

26
Q

Glutaraldehyde concentration

A

3%

27
Q

Glutaraldehyde for immunoelectron microscopy cocnentration

A

0.25%

28
Q

Duration of fixation for most formalin fixatives

A

24 hrs

29
Q

Duration of fixation for buffered formalin

A

2-6 hrs to 1 week

30
Q

Duration of fixation for EM

A

3 hrs

31
Q

Fixation is not required for

A

Microbiological and toxicological studies

32
Q

Rate of penetration of formalin

A

1 mm/hr

33
Q

Penetrate the best

A

(1) formalin (2) alcohol

34
Q

Penetrate the worst

A

Glutaraldehyde

35
Q

Volume pf fixative

A

20x volume of tissue

36
Q

Fixation can be cut down using

A

Heat
Vacuum
Agitation
Microwave (450 watts, 50-55degC, 1.5-4mins)

37
Q

Ideal size of tissues to be fixed

A

-Not more than 2 cm^2 in dm
-Not more than 4 mm thick

38
Q

Ideal number of hours for fixation

A

Biopsy: 6-18 hrs
Standard: 24-72 hrs
Immunogistochemistrt: 12-24 hrs

39
Q

Characteristics of a good fixative

A

“CSSK-PH-IPT-MP”

Histopathology (12 decks)

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