Fixation

Question 1

Fixation is also known as?

Answer 1

Preservation

Question 2

What is the primary goal of fixation? How about the secondary?

Answer 2

Primary - Preserve the morphologic and chemical integrity of the cell.

Secondary - To harden and protect the tissue from trauma of further handling, and easy cutting during gross examination.

Question 3

The most important reaction in fixation is ________.

Answer 3

Stabilization of proteins

Question 4

What will happen to the tissue if it’s left in air for too long?

Answer 4

Dry-out

Question 5

Leaving the tissue in hypotonic solution will cause the tissue to _____.

Answer 5

Swell

Question 6

Leaving the tissue in hypertonic solution will cause the tissue to _____.

Answer 6

Shrink

Question 7

Under the two basic mechanisms in fixation, which one is taken in by the tissue? Give an example.

Answer 7

Additive

Formaldehyde
Osmium tetroxide
Mercuric chloride

Question 8

Under the two basic mechanisms in fixation, which one is not taken in by the tissue? Give an example.

Answer 8

Non-additive

Alcoholic fixatives

Question 9

What is the average pH of a fixative?

Answer 9

7.0 (neutral)

Question 10

The autotechnicon tissue processor has a temperature of _______.

Answer 10

40°-42°C

Question 11

To fix specimens with tuberculosis, the formalin is heated to ______.

Answer 11

100°C

Question 12

In light microscopy, what is the ideal size of tissues to be fixed?

Answer 12

<2cm² in diameter
<4mm thick

Question 13

The best results after fixation can be obtained in _______ solution.

Answer 13

Slighty hypertonic

Question 14

What is the concentration of glutaraldehyde?

Answer 14

3%

Question 15

Why is fixation not required in bacteriologic and toxicologic studies?

Answer 15

Fixatives can kill and prevent the growth of microorganisms, and it can neutralize drugs

Question 16

Formalin diffuses at a rate of approximately _____.

Answer 16

1mm/hr

Question 17

State at least 5 characteristics of a good fixative.

Answer 17

1. Cheap
2. Stable
3. Safe to handle
4. Kill the cells quickly
5. Produce minimum shrinkage
6. Harden the tissues properly
7. Inhibits bacterial decomposition and autolysis
8. Permit rapid and even tissue penetration
9. The optimum osmolality for a specific tissue and fixative type
10. Make cellular components insoluble
11. Permit subsequent application of many staining procedures

Question 18

Give at least 5 examples of simple fixatives.

Answer 18

1. Aldehydes (Formaldehyde, Glutaraldehyde)
2. Metallic Fixatives (Mercuric chloride, Chromic acid, Lead)
3. Picric acid
4. Acetic acid
5. Acetone
6. Alcohol
7. Osmium tetroxide
8. Heat

Question 19

What are the fixatives that preserve the nuclear structures.

Answer 19

Bouin’s fluid
Flemming’s fluid
Newcomer’s fluid
Carnoy’s fluid
Heidenhain’s Susa

Question 20

Formalin is buffered using what?

Answer 20

Phosphate buffer

Question 21

What is the whitish precipitate that forms in a formalin solution when it is stored in a very cold place?

Answer 21

Paraformaldehyde

Question 22

What fixative is best used for nervous tissues?

Answer 22

Formalin

Question 23

Give at least 2 disadvantages of using formalin.

Answer 23

• Troublesome dermatitis of the hands
• Its fumes are irritating to the nostrils
• It may also cause asthma in some allergic individuals
• In tissues containing much blood (spleen), unbuffered formalin leads to the
  formation of dark brown artifact pigment granules.

Question 24

Fixation time of formaldehyde

Answer 24

24 hours

Question 25

What fixative is ideak for silver impregnation?

Answer 25

10% formol-saline

Question 26

Calcium acetate formalin is used to preserve _________.

Answer 26

Phospholipids

Question 27

Why did calcium acetate formalin replace 10% formol-saline as the most commonly used fixative in pathology?

Answer 27

Simple to prepare
Buffered to pH 7 by acetate

Question 28

Best general tissue fixative:

Answer 28

10% buffered neutral formalin