Histology quiz 2

what is the purpose of fixation

to prevent tissue from dying or hardening

how does fixative prevent tissue from dying or hardening

stabilizing the proteins

what is the fixative of choice in most labs

10% buffered formalin

what are the 2 methods of fixation

physical and chemical

what are the 3 ways tissue can be physically fixed

heat, freezing, desiccation (drying)

How does heat fix tissue

denatures and stabilizes the proteins

what is the maximum temperature to be used when using heat to fix tissues

68 C

when is freezing used when physically fixing a tissue

in research, rarely in the clinical setting

when is desiccation (drying) used when physically fixing tissues

when prepping for the application of Wright’s stain

what are the methods of chemical fixation

additives, nonadditives, coagulants and anticoagulants

how do additives chemically fix tissues

proteins in the tissue combine with the fixative to make it insoluble

what can happen when using additives to fix tissue

shape or charge of the protein can change

what are nonadditives

organic compounds such as acetone or alcohol that act on the tissue

how do non additives fix tissue

dissociate the water molecules in the proteins of the tissue to dehydrate it

what can happen when using non additives to fix tissues

shrinking and hardening of tissues

how do coagulants fix tissues

allows solutions to easily penetrate the inside of the tissues

how do non coagulants fix tissues

creates a gel within the tissues so that penetration by solutes is difficult

Go Get Plenty Of Fish, what does the G in go stand for

Glutaraldehyde

Go Get Plenty Of Fish, what does the G in get stand for

Glyoxal

Go Get Plenty Of Fish, what does the P in plenty stand for

Potassium dichromate

Go Get Plenty Of Fish, what does the O in of stand for

Osmium tetroxide

Go Get Plenty Of Fish, what does the F in Fish stand for

formaldehyde

what factors affect fixation

Temperature, size, volume ratio, time, penetration, storage, pH, osmolality

Increase in temperature __________ rate of fixation

increases

increase in temperature __________ the rate of autolysis in unfixed tissues

increases

what can happen if a tissue is too large while being fixed

not enough will be exposed to properly fix

what is the ratio of fixative to tissue

10:1

coagulant fixatives have a __________ penetration

maximum

non coagulant tissues penetrate tissue fast but….

continue to cross link proteins after penetration

how soon should you put tissues in fixative

immediately after collection

how long should tissues remain in fixatives

6-8 hours

what happens if tissue remains in fixative indefinitely

overhardening of tissue

what is the medawar constant

d=k√t

what does d stand for in Medawar constant

depth of penetration in mm

what does k stand for in medawar constant

coefficient of diffusability

what does t stand for in medawar constant

time in hours

what can tissues be stored in indefinitely for further testing

formalin

what does the pH need to be for preservation

7.2-7.4

what does hypertonic mean

high salt concentration. high osmolality, shrinkage of tissue

what does hypotonic mean

low salt concentration. low osmolality and swelling/rupture of tissues

what fixatives are preferred for fixing the nucleus

Acetic acid and Carnoy

what fixatives fix lipids

osmium tetroxide and chromic acid

what is best used to fix glycogen

non aqueous solutions such as alcohol

what happens if fixation is delayed

autolysis can occur

what is the chemical formula for acetic acid

(CH₃ COOH)

what is the chemical formula for formaldehyde

(CH₂O)

what type of fixative is formaldehyde

non coagulant additive

formalin is what type of special fixative

1 of 3 that can form fixation pigment

what is formalin pigment

pigment formed when tissue is fixed using formaldehyde. dark brown crystal pigment that forms when the pH drops below 6.0

how do you treat formalin pigment

alcoholic picric acid or alkaline alcohol

what is the chemical compound for glutaraldehyde

(C₅H₈O₂)

what type of fixative is glutaraldehyde

non coagulant additive

what is the chemical compound for glyoxal

(C₂H₂O)

what kind of fixative is glyoxal

non coagulant additive

what is the chemical compound for mercuric chlordie

(HgCl₂)

what kind of fixative is mercuric chloride

coagulant additive

what is special about mercuric chloride

1 of 3 fixative to form fixation pigment. mercury pigment that is brown.

how to treat mercury pigment

treated with iodine to oxidize mercury and then sodium thiosulfate to remove excess iodide.

what type of fixative is picric acid

coagulant additive

what is the chemical formula for osmium tetroxide

(OsO₄)

what type of fixative is osmium tetroxide

non coagulant additive

what is the chemical compound for potassium dichromate

(K₂Cr₂O₇)

what type of fixative is potassium dichromate

non coagulant additive

what is special about potassium dichromate

1 of 3 fixatives to cause fixation pigment. chrome pigment

how to treat chrome pigment

treat with water before processing, remove with acid alcohol

what are the characteristics of alcohols

dissolves fats, overhardens and shrinks tissues, dehydrates

what kind of fixative is alcohols

non additive coagulant

what type of fixative is acetone

non additive coagulant

what are the characteristics of acetone

causes shrinking, hardening and distortion of tissue, rapid fixation, not a good fixative

what is acetone mainly used for

fixing brain tissue

compound fixatives work by…

counteracting the negative effects of the individual components

what is in bouin

picric acid, formaldehyde, glacial acetic acid

what is bouin used for

excellent cytoplasmic staining, excellent for GI tissues and endocrine tissues

what is in gendre

saturated alcoholic picric acid, formaldehyde, glacial acetic acid

what is gendre used for

preserving glycogen

what is in hollande

saturated aqueous picric acid, paraformaldehyde, phosphate buffer, distilled water

what is hollande used for

GI biopsies

what is in stock B5

mercuric acid, sodium acetate, distilled water

what is in working B5

stock + formaldehyde

what is the ratio of stock to formaldehyde in B5

10:1

what is B5 used for

hematopoietic or lymphoreticular tissues, good for antigens

what is in the stock of Zenker and Helly

mercuric chloride, potassium dichromate, sodium sulfate, distilled water

what is in working zenker

stock + glacial acetic acid

what is zenker used for

nuclear staining and as a fixative for muscle striations

what is in working helly

stock + formaldehyde

what is in zamboni

saturated aqueous picric acid, paraformaldehyde, phosphate buffer, distilled water

what is zamboni used for

primary fixative for electron microscopy

what is in orth stock

potassium dichromate, sodium sulfate, water

what is in working orth

stock + formaldehyde

what is orth used for

helping the diagnosis of pheochromocytoma

what is in 4CF-1G

formaldehyde, glutaraldehyde, sodium hydroxide, phosphate buffer

what is 4CF-1G used for

a dual purpose fixative

what is in davidson

95% ethanol, 10% neutral buffered formalin. glacial acetic acid distilled water

what is davidson used for

fixation of eye and testes specimens

what is in carnoy

absolute ethanol, chloroform, glacial acetic acid

what is carnoy used for

preservation of glycogen, nuclear preservation, extraction of lipids

what is in clarke

absolute alcohol and glacial acetic acid

what is clarke used for

microanatomical preservation

what is in michel

citric acid, ammonium sulfate, N-ethylmaleimide, magnesium sulfate, distilled water

what is michel used for

kidney biopsies