Week 4: Fixations

Question 1

This is done to
prevent the decomposition and drying
of tissue samples so that it can be
processed in the laboratory.

Answer 1

Fixation

Question 2

This process is also considered
the first and most critical step
in histotechnology.

Answer 2

Fixation

Question 3

o Heating (blue flame),
microwaving, cryopreservation
(freeze-drying)

Answer 3

Physical fixation

Question 4

o Achieved by immersing the 
specimen in a fixative or by 
perfusing the vascular system 
with fixative
o For specialized histochemical 
procedures, fixatives can be 
applied in vapor form

Answer 4

Chemical fixation

Question 5

Fixatives chemically link/add
themselves on to the tissue
giving stability to the protein

Answer 5

Additive fixation

Question 6

Example of additive fixation

Answer 6

formalin, mercury, osmium

tetroxide

Question 7

Example of non-additive fixation

Answer 7

acetone, alcohols

Question 8

Fixation ph

Answer 8

6-8

Question 9

What happens in tissue hypoxia?

Answer 9

Lower the pH of the solution

Question 10

What temperature is sufficient to maintain excellent

morphology of tissues

Answer 10

room temperature

Question 11

What temperature is used for regular tissue processing

Answer 11

40°C

Question 12

What temperature is used for electron microscopy and

some histochemistry

Answer 12

0-4°C

Question 13

What fixative is used for osmolarity?

Answer 13

Normal phosphate buffered

saline (PBS)

Question 14

Concentration of fixative in routine laboratory

Answer 14

10% formaldehyde

Question 15

Concentration of fixative in immune electron microscopy

Answer 15

3%
glutaraldehyde, 0.25%
glutaraldehyde

Question 16

commonly used in

routine laboratory

Answer 16

formalin

Question 17

Made up of only one 
component substance 
(e.g. Formaldehyde, 
HgCl, acetone, alcohol, 
glutaraldehyde)

Answer 17

Simple

Question 18

Made up of two or more
fixatives which have been
added together

Answer 18

Compound

Question 19

Example: Helly’s solution 
(made up of 
formaldehyde, mercurric 
chloride and potassium 
dichromate, Gendre’s 
fixative (ethyl alcohol, 
formaldehyde, glacial 
acetic acid)

Answer 19

Compound

Question 20

Permits general 
microscopic study of 
tissue structures without 
altering the structural 
pattern and normal (e.g. 
10% formol saline, 
Heidenhain’s Susa)

Answer 20

Microanatomical fixatives

Question 21

Preserves specific

elements of the cell

Answer 21

Cytological fixatives

Question 22

Failure to arrest early

autolysis of cells

Answer 22

Failure to arrest early

autolysis of cells

Question 23

Removal of substance

soluble in fixing agent

Answer 23

Wrong choice of fixative

Question 24

Presence of artefact
pigments on tissue
sections

Answer 24

Incomplete washing of

fixative

Question 25

Tissues are soft and | feather-like in consistency

Answer 25

Incomplete fixatio

Question 26

Loss or inactivation of | enzymes needed for study

Answer 26

Wrong choice of fixative

Question 27

Shrinkage and swelling of | cells and tissue structure

Answer 27

Over fixation

Question 28

Tissue blocks are brittle | and hard

Answer 28

Prolonged fixation

Question 29

is the process of placing an already fixed tissue in a second fixative in order

Answer 29

Secondary fixation

Question 30

``` is a form of secondary fixation whereby a primarily fixed tissue is placed in aqueous solution of 2.5-3% potassium dichromate for 24 hours to act as mordant for better staining effects and to aid in cytologic preservation of tissues ```

Answer 30

Post-Chromatization

Question 31

``` It is a polymerized form of formaldehyde, usually obtained as a fine white powder, which depolymerizes back to formalin when heated ```

Answer 31

Paraformaldehyde

Question 32

It is suitable for paraffin embedding and sectioning, and also for immunocytochemical analysis

Answer 32

Paraformaldehyde

Question 33

It is a dialdehyde – made up of two | formaldehydes

Answer 33

Glutaraldehyde

Question 34

➢ Most frequently used for the fixation of specimens for electron microscopy ➢ But not good for immunohistochemical staining

Answer 34

Glutaraldehyde

Question 35

10% formal-saline

Answer 35

Aldehyde

Question 36

suitable blood films or cell | cultures

Answer 36

Methanol

Question 37

very good for cytologic smears o Example: PAP smears

Answer 37

Alcohols

Question 38

It is excellent for fixing dry and wet smears, blood smears and bone marrow tissues

Answer 38

100% Methyl Alcohol

Question 39

It is used at concentrations of | 70-100%

Answer 39

Ethyl Alcohol

Question 40

``` It is considered to be the most rapid fixative and may be used for urgent biopsy specimens for paraffin processing within 5 hours ```

Answer 40

Carnoy’s Fixative

Question 41

used | on frozen sections and smears

Answer 41

Clarke’s solution

Question 42

``` o It can be used for rapid diagnosis because it fixes and dehydrates at the same time, e.g., in the frozen section room o It is good for preservation of glycogen ```

Answer 42

Gendre’s Fixative

Question 43

This is recommended for the fixing of mucopolysaccharides and nuclear proteins

Answer 43

Newcomer’s Fluid