PAS & PASD Flashcards
What is PAS
target tissue component
staining principle
positive control
carbohydrate stain
targets: Group 1 CHO
-neutral poly sacc (NON IONIC homoglycans)
glycogen, thyroglobulin, fungi, chitin, starch
Staining principle: histochemical
positive controls: liver, kidney, and muscle
What are some properties of carbohydrates
- aldehydes and ketones
-dont ionize so many dyes cant attach to them
-glucose joined by covalent bonds therefore nothing can bind
how do we attach dyes to glucose
1st step
create a reactive group
-oxidation with periodic acid to break the bonds producing aldehyde groups that can bind with dye molecules
periodic acid is a weak oxidizer why dont we use a stronger one - we dont want to over oxidize to carboxyl groups C=OH which are non reactive , a false negative reaction
but next problem - NO dye group that can bind to aldehydes
how do we attach dye molecules to aldehydes
Schiff Reagent - can be done with any dye but pararosanalin is most popular
took pararosanalin (dye because it has a quinoid ring) added sulphurous acid to make leucofuchsin = a reduced dye
color is lost because we dont have the H bonds
What is step 2 in processing
Staining
Add the colorless schiff reagent to dialdehyde groups in tissue - they will bind to SO3H groups = restores the quinoid ring structure = colored product
Bright magenta
pink = old
What is step 3 in staining
counterstaining
-need to demonstrate other tissue components
-contrast coloring
Hematoxylin - regressive
Alcian blue - carb stains muceins
PAS targets?
use composite block to ensure multiple targets are staining appropriately
Basement membrane of kidney of glomerlus - line that surrounds it
Colon - neutral polys
brunners glands of duodenum - mucin stained - PAS positive
Thyroid- thyroglobulin
Fungi walls
Cryptococcus
Amyloid - in brain
if the pathologist is looking specifically for glycogen theyll need to order a confirmatory test = PAS Diastase
Diastase breaks down glucose which is then soluble in water
Two control slides - one that shows presence of glucose - positive
one that is negative
How do confirm if there is glycogen
PAS/D
Diastase - digests polysaccharides into monosaccharides that are water soluble
-done the same way as PAS except the digestion step is done first
Where can glycogen be found
Liver
Cardiac and skeletal muscles
hair follicles
endometrial glands
vaginal and ectocervical epi
umbilical cord
mesothelial cells
neutrophils and megakaryocytes
HOWEVER KUPFFER CELLS ARE PAS/D RESISTANT
What are the factors that affect staining
Use a fixative that preserves glycogen, ethanol alcohol based preservative and formalin
if you use old or incorrectly stored Schiffs reagent itll give false results dont use Schiffs reagent that has turned pink .
Dye that has not been reduced will not dye the target tissue component
Glycogen streaming artifact
diffusion of unfixed material
Staining of PAS result
nucleus - blue
glyvogen - magenta
PAS + = magenta
periodic acid helps to
oxidize tissue to prep for staining
cheaper version of distase
spit
