Fixation

Question 1

_____________ is the use of physical and chemical methods, to prevent changes associated with tissue decay.

Answer 1

Fixation

Question 2

State three physical methods of fixation.

Answer 2

Heating, freezing, and microwaving

Question 3

Heating coagulates tissue ________.

Answer 3

Proteins

Question 4

Freezing in _________ _________ or carbon dioxide causes water within the tissues to crystallise, forming a solid matrix.

Answer 4

Liquid nitrogen

Question 5

Coagulants (such as acetone and alcohols), cross-linkers (such as formalin), and unclear (such as mercuric chloride) are all _________ fixation methods.

Answer 5

Chemical

Question 6

Chemical methods use solutions to __________ tissues, ‘fixing’ all of the components in place.

Answer 6

Permeate

Question 7

Cross-linkers, such as formaldehyde and glutaraldehyde, form ___________ bridges between side- and end-groups of proteins, creating a solid protein mesh, linked by methyl groups, in a protein-COO-CH2-HN-protein formation.

Answer 7

Methylene

Question 8

Formaldehyde, or _________, is the fixative of choice in the majority of laboratories.

Answer 8

Formalin

Question 9

In formalin, _________ _________ reacts with proteins in the sample to form methylene bridges.

Answer 9

Methylene glycol

Question 10

Cytoplasmic streaming is a form of uneven staining, observed when carbohydrates are pushed to the sides of the subject tissue. It is often observed after __________ use.

Answer 10

Formalin

Question 11

______________ offers the best morphological preservation.

Answer 11

Glutaraldehyde

Question 12

State the chemical formula of glutaraldehyde.

Answer 12

CHO.(CH2)3.CHO

Question 13

Ethanol, methanol, and acetone are examples of ___________.

Answer 13

Coagulants

Question 14

What is the main disadvantage of coagulants?

Answer 14

They cause shrinkage, with poor preservation of mitochondria

Question 15

Osmium tetroxide is an oxidising agent, and a secondary fixative, which turns black when fixing ________.

Answer 15

Lipids

Question 16

A mixture of fixatives, buffers, and salts, which act together, to give best fixation of tissue, is a ____________ fixative.

Answer 16

Compound

Question 17

List three compound fixatives.

Answer 17

Zenker’s, Carnony’s, and Bouin’s

Question 18

True or false: compound fixatives may be responsible for over- and under-fixation, antigen masking, and fixation-related deposits.

Answer 18

True

Question 19

Most tissues, with the exception of muscle biopsies for enzyme histochemistry, and skin and __________ biopsies for investigation of inflammatory skin conditions, are suitable candidates for fixation.

Answer 19

Mucosal

Question 20

Preservation, or fixation, prevents ____________ and putrefaction of cells and tissues.

Answer 20

Autolysis

Question 21

__________ refers to nuclear fading.

Answer 21

Karyolysis

Question 22

Pyknosis is __________ shrinking.

Answer 22

Nuclear

Question 23

______________ is nuclear fragmentation.

Answer 23

Karyorrhexis

Question 24

Nuclear dissolution leads to an ______________ necrotic cell.

Answer 24

Anuclear

Question 25

Give four characteristics of an ideal fixative.

Answer 25

Prevention of decomposition, enhancement of staining, preservation of tissue volumes, and non-toxicity

Question 26

In a strong acid environment (low pH), the primary target groups on proteins become unreactive to ____________.

Answer 26

Formaldehyde

Question 27

At low pH, the ____________ effects of formaldehyde are reduced.

Answer 27

Crosslinking

Question 28

Time of fixation is equal to the __________ the fixative must penetrate.

Answer 28

Distance

Question 29

Gross specimens should be ______________ in fixative, not saturated.

Answer 29

Suspended

Question 30

Diffusion of molecules increases in _________ temperatures.

Answer 30

Raised

Question 31

Formalin stronger than ___% causes hardening and shrinkage.

Answer 31

10

Question 32

Ethanol weaker than ___% cause a lack of dehydration.

Answer 32

70

Question 33

Best fixation results are obtained in a slightly ____________ solution.

Answer 33

Hypertonic

Question 34

Hypotonic solutions cause _________.

Answer 34

Shrinkage

Question 35

___________ solutions can cause swelling of tissue.

Answer 35

Hypertonic

Question 36

In the case of CD20 marker analysis, a lack of a __________ positive stain indicates poor fixation.

Answer 36

Brown

Question 37

Decalcification is performed on _______ samples.

Answer 37

Bone