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UND 363 PAS

QuestionAnswer
PAS demonstrates what glycogen in liver, basement membrane, fungus (organisms with high carbohydrate content in cell wall)
PAS principle periodic acid oxidises certain elements which in turn react with schiff reagent
schiff reagent is __________ and is made of what 3 components colorless, basic fuschin, soduim metabisulfate and 1N HCL
what occurs to schiff reagent before and after water rinse fuschin binds with new aldehyde groups that were created from P.acid oxidation. Runnig water after schiff causes fuschin to turn pink/red from molecular changes
what counter stains can be used with PAS Hematoxylin (for fungal a lt green or fast green can be used)
what fixatives can be used with PAS 10% NBF, bouins *if doing blood smears with PAS they need to be fixed for 10-15 min with methanol first*
what fixatives CANNOT be used with PAS and why Gluteraldehyde (a dialdehyde), the extra aldehyde will react with schiff reagent, Chromic acid or potassium permangenate - will oxidize beyond the reactive aldehyde stage
what is the preferred thickness for PAS KIDNEY 1-2 micron, others 4-5 microns
what microscope should be used light
what is the proper (best) control spec for PAS. What if glycogen is to be demonstrated? Kidney is the most sensitive (cut at 1-2 micron). For glycogen - then liver or cervix (endocervical canal and ectocervix)
why could liver be a drawback as a control for PAS Liver can have a weak reaction and lead to false positive if it contains large amts. of glycogen.
what are the 5 major reagents for PAS periodic acid, schiff reagent, potassuim metabisulfate rinse, running water, harris hematox
what does the periodic acid do in PAS oxidises glycols to aldehydes - breaks down carbon chains and converts to aldehydes *the change to aldehydes completes the oxidation*
what does the schiff reagent do in PAS (2 stages) it combines with the aldehydes from P.A., it first is formed as a colorless compound, and secondly is colored via quinoid chromophore group restoration due to running water
what does the potassium metabisulfate rinse do in PAS removes excess schiff reagent and prevents false colorization (due to the oxitadation)
what does the running water do in the PAS reestablishes quinoid structure and color
what are the counters stains for PAS harris hematox, and fast green for fungal
what are the expected results for PAS PAS positive material - pink to reddish, background will be lt blue (harris), or green if fast green used
PAS staining depends on 4 things 1. # of 1,2 glycol group (ie aldehydes present) 2. reactivity of schiff with reaction product 3. structure of oxidized polymer 4. procedural conditions (ie increase/decrease incubation time in P.A or schiff will increase/decrease stain intensity
what problems can occur if over cholorinated water is used to rinse can overoxidize sections and give non-specific staining
to determine if any previous reactive aldehyde groups are present in tissue what can be done a control slide should be run through all steps except Periodate oxidation step.
what problems can a chromate fixative cause over oxidize reactive groups during fixation and resulting schiff reaction will be weak AVOID chromatic fixatives (ie Zenkers, Hellys, orths)
schiff reagent needs to be stored and used how stored in fridge, must come to room temp before use. if used too early (cold) with will result in a weak stain
what are 2 ways PAS can be tested for viability. how long is it usually stable stable for 2-4 months CHEMICALLY (10 ml 37% formaldehyde, few drops shiff, if good it will be red/purple immediate, if bad blue/purple and delayed HISTOLOGICAL - stain cross section of appendix (should see fine red mesh work between smooth muscle)
Created by: mustangvxd
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