Fixation

Chapter 4

what digest cell in autolysis

enzymes

what digest cell putrefaction

bacteria

what prevents digestion

fixation

what helps to increase contrast between structures

refractive index

what is the primary target for stabilization

proteins

what is a mordant

link dye to tissue

what is a physical method of fixation

heat

what is the cause of overstained nuclei

over heat tissue

what are additive fixative

chemically link to tissue

What are non additive fixatives

act on tissue but do not combine

what are examples of non additive fixatives

acetone and alcohol

how do non additive fixatives react with tissue

remove bound water

what is coagulating fixative

easily penetrates tissue

what is noncoagulating fixative

gel makes penetration difficult

how thick should sections be for routine fixation

less than 3 mm

what volume should the fiative be compared to the tissue

20x

what does high temperature do for fixative

increase rate

what is ischemic time

time between blood supply loss and fixation

how long should tissue be fixed in formalin

6-8 hours

what is a artifact of formalin fixation

nuclear bubbling

what happens during fixative when IF of IHC is needed

no fixation

what solution does formalin fixed tissues get stored in

70 alcohol

what type of solution is it when there is more particles outside the cell than inside

hypertonic

what happens to the cell when the solution is hypertonic

shrinks

what happens to the cell when placed in hypotonic solution

swells

what type of solution is it when there is less particles outside than inside

hypotonic

what are the preferred fixatives for nucleic acids

Acetic alcohol and carnoy

what is acetic alcohol and carnoy solutions the preferred fixative for

nucleic acid

what causes nuclear bubbling

incomplete fixation in NBF

what happens to proteins when fixed in an additive fixative

tertiary structure changes

why does the tertiary structure changes in an additive fixative

electrical charges changes

what fixatives insolubilize lipids

osmium tetroxide and chromic acid

what is the function of osmium tetroxide and chromic acid

preserve lipids

what types of fixative is osmium tetroxide

additive

what does osmium tetroxide react with

double bonds of unsaturated lipids

what is thought to preserve carbohydrates

crosslinked proteins

what does acetic acid preserve

nucleic acids

what is the main disadvantage of of acetic acid

protein swelling

what does acetic acid do to the tissue

soft and swell

what is the pH of acetic acid to allow swelling of tissue

4

what is the effect that acetic acid have on RBCs

lyses

what percentage of formaldehyde are stock solutions

37-40

what percentage of formalin are stock solutions

100

how to prepare 10% formalin solutions

9 parts water 1 part stock formaldehyde

what percentage of formaldehyde is 10% formalin

3.7-4.0

what is paraformaldehyde

longer polymeric form of formaldehyde

what media is paraformaldehyde found in

solid powder

what type of fixative is formaldehyde

additive noncoagulant

what chemical groups does formaldehyde react with

amines, thiols and purines

what is the cross linkage of aldehyde complex with functional groups called

methylene bridge

what is a methylene bridge

aldehyde and function group cross link

what is the rate of penetration for formaldehyde

fast

what is the rate of cross linking reactions

slow

what occurs after 48 hours of fixation in formaldehyde

overfixation

what happens if tissue is underfixed in formaldehyde

redenatured by alcohol and heat

what step in formaldehyde fixation is reversible

addition

what is preserved by formaldehyde

lipids

what are lipids dissolved by

alcohol and xylene

what can be added to formalin to preserve lipids

calcium salts

why does formalin pigment form

acidic ph

what does formaldehyde do to tissue

harden

what forms when formaldehyde reacts with oxygen

formic acid

what is a characteristic of formalin pigment

reduce silver

how is formalin pigment removed

alcoholic picric acid 

where is formalin pigment depositied

on top of tissue

what is the best use of calcium formalin

phospholipids

what is best use of formalin ammonium bromide

CNS

what should be added to formalin when fixing CNS

ammonium bromide

what type of formalin can be used for EM

modified millonig

what type of formalin is helpful for processing

alcoholic

what is the maximum concentration recommended for alcoholic formalin

70%

what is the TWA for formaldehyde

0.75 ppm

how long is the TWA measured

8 hours

what is the STEL for formaldehyde

2 ppm

how long is the STEL measured

15 min

what is the action level of formaldedhyde

0.5 ppm

how long is the action level measured

8 hours

what happens if the PEL is above 0.75 ppm

corrective action

how does glutaraldehyde differ from formaldehyde chemically

dialdehyde

what happens when schiff reagent is used on glutaraldehyde fixed tissues

false positive

why does schiff reagent produce a false positive on glutaraldehyde fixed tissues

reacts with free aldehyde

at what rate does glutaraldehyde penetrate

slow

what happens when tissue is left in glutaraldehyde

overhardens

how long should tissue fix in glutaraldehyde

2 hours

what breaks down glutaraldehyde

oxygen

what does glyoxal react with

oxygen end groups and amines

what do mercuric salt do to tissue

shrink

what type of fixative is mercuric chloride

addivitve

what group does mercuric chloride react with

sulfhydryl

what amino acid contains sulfhydryl groups

cysteine

how is mercury pigment removed

iodine and sodium thiosulfate

where is mercury pigment deposited

on top of tissue

what types of dyes does osmium tetroxide accept

basic

what is unique about picric acid

both a fixative and stain

what does picric acid do to DNA

lyses

what type of fixative is picric acid

additive

what type of dyes does picric acid accept

acidic