What is the first stage of tissue processing?
Dehydration – the removal of water and fixative from the tissue
What is the purpose of the clearing stage in tissue processing?
Removal of dehydrating solutions, making the tissue receptive to the infiltration media
What occurs during the infiltration stage of tissue processing?
Permeating the tissue with the support media
What is embedding in the context of tissue processing?
Orienting the tissue sample in a support media and allowing it to solidify
What are the two special techniques that occur before dehydration?
- Decalcification
- Frozen sectioning
When is decalcification performed in the tissue processing sequence?
Usually done after fixation but before the dehydration step
What must be removed from tissue prior to embedding unless special studies are requested?
Calcium
What are the two methods for removing calcium from tissue?
- Acid methods
- Chelating agents
How do acid methods affect the stainability of the tissue?
Acid will have some effect on the stainability of the tissue
What is the role of chelating agents in decalcification?
Organic compounds that bind certain metals, such as EDTA binding calcium ions
What should be done after decalcification?
Rinse the sections with running water
What methods can be used to test the adequacy of decalcification?
- Mechanical methods
- Chemical methods
- Radiographic methods
True or False: Mechanical methods for testing decalcification are highly accurate.
False
What is the chemical method for checking decalcification based on?
Precipitation of calcium oxalate with the addition of ammonium hydroxide and ammonium oxalate
What is the most accurate method for determining if decalcification is complete?
Radiographic methods
What precautions should be followed when using decalcifying agents?
Proper PPE and acid precautions
When are frozen sections typically performed?
When a rapid diagnosis is needed or when a staining technique will not work
What is a cryostat?
A microtome in a refrigeration unit used to freeze tissue for rapid diagnosis
What are the two types of tissue processors?
- OPEN (tissue transfer)
- CLOSED (fluid transfer)
What is a disadvantage of open tissue processors?
Health and fire hazards due to open reagent containers
What is a key feature of closed tissue processors?
The tissue remains in a stationary retort with reagents pumped in and out
What is the fluid interchange that occurs during tissue processing?
Fluid exchange between the fluid in the tissue and the surrounding fluids
What are the five factors that influence the rate of processing?
- Agitation
- Heat
- Vacuum
- Viscosity
- Fixation
How does agitation affect fluid exchange during tissue processing?
Increases the flow of the solutions around the tissues
