Fixation

Question 1

First and most critical step

Answer 1

Fixation

Question 2

Primary aim

Answer 2

To preserve in life-like manner

Question 3

Secondary goal

Answer 3

To harden and protect

Question 4

The most important reaction

Answer 4

Stabilization of proteins

Question 5

Stabilization of proteins can be achieved by

Answer 5

Forming cross-links between proteins

Question 6

Fixes tissues by forming cross-linkage between lysine residues

Answer 6

Formaldehyde

Question 7

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

Answer 7

Additive

Question 8

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

Answer 8

Non-additive

Question 9

pH in fixation

Answer 9

6.0-8.0

Question 10

pH of normal phosphate buffered saline-based fixative

Answer 10

7.0

Question 11

Usual temp

Answer 11

RT (18-30degC)

Question 12

Tissue processor temp

Answer 12

40-42degC

Question 13

EM and histochem temp

Answer 13

0-4degC

Question 14

Mast cells for EM temp

Answer 14

RT

Question 15

Slows down decomposition if tissue cannot be fixed immediately

Answer 15

Refrigeration

Question 16

Rapid dixation of urgent biopsy specimen

Answer 16

Formalin heated to 60degC

Question 17

Fix tissues with tuberculosis

Answer 17

Formalin heated to 100degC

Question 18

Thicknes of sections for EM

Answer 18

1-2 mm^2

Question 19

Thicknes of sections for light microscopy

Answer 19

2 cm^2

Question 20

Thicknes of sections for thin LM

Answer 20

0.4 cm or 4 mm

Question 21

Large solid tissues like uterus should be

Answer 21

Opened/sliced thinly

Question 22

Brain is usually suspended in ___ for ___

Answer 22

10% NBF; 2-3 weeks

Question 23

Osmolality for best results are obtained using

Answer 23

Slightly hypertonic (400-450 mOsm)

Question 24

Added to osmium tetroxide fixatives for EM

Answer 24

Sucrose

Question 25

Formaldehyde concentration

Answer 25

10%

Question 26

Glutaraldehyde concentration

Answer 26

3%

Question 27

Glutaraldehyde for immunoelectron microscopy cocnentration

Answer 27

0.25%

Question 28

Duration of fixation for most formalin fixatives

Answer 28

24 hrs

Question 29

Duration of fixation for buffered formalin

Answer 29

2-6 hrs to 1 week

Question 30

Duration of fixation for EM

Answer 30

3 hrs

Question 31

Fixation is not required for

Answer 31

Microbiological and toxicological studies

Question 32

Rate of penetration of formalin

Answer 32

1 mm/hr

Question 33

Penetrate the best

Answer 33

(1) formalin (2) alcohol

Question 34

Penetrate the worst

Answer 34

Glutaraldehyde

Question 35

Volume pf fixative

Answer 35

20x volume of tissue

Question 36

Fixation can be cut down using

Answer 36

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

Question 37

Ideal size of tissues to be fixed

Answer 37

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

Question 38

Ideal number of hours for fixation

Answer 38

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

Question 39

Characteristics of a good fixative

Answer 39

“CSSK-PH-IPT-MP”