FIXATION

Question 1

TYPES OF FIXATION

Answer 1

PHYSICAL METHODS
FREEZE DRYING AND FREEZE SUBSTITUTION 
CHEMICAL FIXATION 
DEHYDRANT COAGULANT FIXATIVES
NON-COAGULANT CROSS LINKING FIXATIVES

Question 2

PHYSICAL METHODS

Answer 2

HEAT FIXATION

MICROWAVE FIXATION

Question 3

is useful in studying soluble materials and small molecules

tissues are cut very thinly, immersed in liquid nitrogen, and the water is removed by vacuum chamber at temperatures of _

Tissue can be post-fixed with formaldehyde vapor

Answer 3

FREEZE DRYING

-40°C

Question 4

__, tissues are immersed in cold (-40°C) fixatives such as _ or _, which slowly remove water by dissolution of ice crystals and the proteins are not denatured.
Bringing the temperature gradually to __ will complete the fixation process

Answer 4

In FREEZE SUBSTITUTION
acetone or alcohol
4°C

Question 5

utilizes organic and non-organic solutions to maintain adequate morphological preservation

Answer 5

CHEMICAL FIXATION

Question 6

acts by coagulating proteins and thus making them insoluble

Answer 6

COAGULANT FIXATIVES

Question 7

DEHYDRANT COAGULANT FIXATIVES

Answer 7

Alcohols and acetone

Question 8

NON-COAGULANT CROSS LINKING FIXATIVES 10

Answer 8

Aldehydes
Gluteraldehyde
Formaldehyde
Chloral hydrate
Glyoxal
Metal salts
Mercuric chloride
Zinc chloride
Metallic compounds
Osmium tetroxide

Question 9

Coagulates nucleic acids but does not fix or precipitate proteins

Answer 9

ACETIC ACID

Question 10

Can penetrate hydrophobic domains of proteins and anion produced (C-COO-) reacts with charged amine groups
This action thus precipitates proteins and extracts nucleic acids

Answer 10

TRICHLOROACETIC ACID(Cl3CCOOH)

Question 11

Dissolves in water to form a weak acid solution (pH 2.0)

It forms salts with basic groups of proteins, causing proteins to coagulate

Answer 11

PICRIC ACID

Question 12

is the most commonly used fixative used in diagnostic pathology

Answer 12

Formaldehyde in its 10% buffered form (NBF)

Question 13

is a vapor then when completely dissolved in water forms a solution containing 37-40% formaldehyde (This aquaeous solution is called __)

Answer 13

Pure formaldehyde

FORMALIN

Question 14

Commonly used buffers are 5

At an acidic pH, unbuffered formalin produces hemoglobin degradation by-products of brown-black, insoluble crystalline birefringent pigment – formation of undesirable pigments are dependent on how the solution becomes very acidic (pigment forms at a ph__)

Answer 14

phosphates, cacodylate, bricarbonate, TRIS, and acetate

pH of 5.7

Question 15

Additives include 4

Addition on no-electrolyte solutions like 3 also improve fixation

Answer 15

Calcium chloride,
potassium thiocyanate,
ammonium sulfate
potassium dihydrogen phosphates

sucrose, dextran, and detergents

Question 16

Fixation is at least 2 weeks

Answer 16

BRAIN

Question 17

RENAL BIOPSIES

!!

Answer 17

Carson’s modified Millonig’s fixative or 2% buffered gluteraldehyde (pH 7.3)

Question 18

MERCURIC FIXATIVES

iodine treatment followed by sodium thiosulfate.

Answer 18

Zenker’s fluid
Helly’s fluid
Schaudinn’s solution
Ohlmacher’s solution
Carnoy-Lebrun Fixative
B5 fixative

Question 19

DICHROMATE FIXATIVES
Tissue should be washed after fixation and transferred to 70% ethanol. Failure to do so may cause pigments to precipitate.

Answer 19

Orth’s solution
Regaud’s solution
Miller’s solution

Question 20

PICRIC ACID FIXATIVES

Answer 20

Bouin’s fluid

Hollande’s solution

Question 21

DEHYDRANT FIXATIVES 3-4 hours of fixation

Answer 21

Absolute ethanol
95% ethanol
70-95% ethanol
100% methanol
100% acetone

Question 22

is useful for touch preparations and smears especially blood smears
In general most alcohol fixatives should be prepared not more than 1-2 days before use.

Answer 22

METHANOL

Question 23

is useful to open membranes of intact cells to facilitate entrance of large molecules.

Answer 23

Cold acetone

Question 24

produces extensive shrinkage and hardening and causes microscopic distortions. Used in immunohistochemistry, enzyme studies and detection of rabies.

Answer 24

Acetone