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Embedding
Lab
| Question | Answer |
|---|---|
| Supporting/embedding medium __ | Holds cells & intercellular structures in proper relationship |
| Most popular embedding medium? | Paraffin wax |
| As paraffin melting point increases ___ | Paraffin becomes harder, provides better support |
| As paraffin melting point decreases __ | Paraffin becomes softer, provides less support |
| Harder paraffin easier__ | Thin sections |
| Softer paraffin easier __ | Ribboning |
| Most common paraffin melting point? | 55 °C to 58 °C |
| Sections may be processed at edge, soft in middle because? | Sections too thick for good infiltration |
| Fix inadequately processed blocks b/c thick tissue? | Trim unprocessed tissue off, embed, Trim sections down, xylene, tetrahydrofuran, xylene, re-infiltrate, embed |
| Carbowax embedding media are? | Water-soluble waxes, polyethylene glycol+wax, blocks aren't permanent, dry up |
| Use of carbowax media doesn't require? | Dehydration & clearing - waxes infiltrate directly from aq. fixatives, fat preserved |
| Carbowax won't infiltrate? | Tissue w/ lots of fat, CNS infiltration v slow |
| Biggest problem w/ Carbowax + fix? | Sections dissolve & "float out" on bath; To help add to bath : potassium dichromate+gelatin+water, diethylene glycol+formaldehyde +Carbowax+water |
| Carbowax sections are cut__? | Chilled, 3 to 5 μm |
| Celloidin is? | Any nitrocellulose embedding medium, use w/ any fixative |
| Most commonly used celloidin? | Parlodion |
| Celloidin sections can be cut? | Wet; keep wet w/ 80% until stained Dry: infiltrate w/ cedarwood oil first |
| Celloidin great for? | CNS |
| Celloidin not often used b/c? | Processing slow (weeks to months), uses very hazardous & explosive reagents, blocks can't be stored long |
| Celloidin processing does not require? | Heat; less damage to tissue |
| GMA embedding medium | Glycol methacrylate, acrylic resin, tolerates some water |
| GMA good for? | Undecalcified bone, bone marrow, kidney, lymph node biopsies |
| GMA staining is__ | More difficult than paraffin, some stains impossible b/c medium not removed from sections |
| Epoxy resins require__ | Dehydrant & transitional fluid (like clearing agent for paraffin) |
| Most common epoxy transitional fluid? | Propylene oxide |
| Most common epoxy resins? | Araldite, Epon, & Spurr's, may cause dermatitis |
| Epoxy section thickness? | Normal: 60-90 nm, thick: 0.5 μm |
| Agar & gelatin media used to? | Make block w/ friable tissue Maintain specimen orientation during processing (double impregnation) Make frozen blocks (harden w/ formalin) |
| 30% Sucrose use | Infiltrate formalin-fixed, unprocessed tissue for frozen blocks |
| Tissue to be embedded diagonally? | Hard tissues, e.g. bone |
| Tissue to be embedded on-edge? | Tissues w/ wall or epithelium e.g. cysts, gallbladder, GI, skin, orient so knife through softest surface first |
| Tissues to be embedded in cross-section? | Tubular structures |
| Forceps metastasis | Fragments of tissue from one block are transferred to another on forceps, can lead to misdiagnosis, clean forceps between blocks |
| Blocks should be cooled quickly so__? | Smaller paraffin crystals form, better support |
| Too much heat during processing or embedding may? | Overfix/overharden tissue, negatively affect stainability |
| Celloidin processing procedure | Dehydrate w/ equal parts 95% & 100%, Treat w/ equal mix 100%+ether, Infiltration w/ celloidin mixed w/ equal parts 100% & ether |
| Celloidin infiltration procedure | Starts at 2% celloidin, gradually up to 12% to 14% celloidin Blocks hardened w/ chloroform |
| Microchatter | Parallel tears in tissue potentially caused by overprocessed/overdehydrated tissue |
| Sponge artifact | Caused by dry sponges being compressed into tissue |
| Best embedding medium for high-resolution light microscopy? | GMA |
| Temperature of melted paraffin used for embedding? | 2°C to 4°C above melting point |
| Polyethylene glycol can be used as embedding medium for? | Lipids |
| OCT compound | Optimal cutting temperature compound; water-soluble embedding medium, freeze quickly w/ liquid nitrogen, frozens |
| Other terms for embedding? | Casting, blocking |