Embedding & Specimen Orientation Flashcards
Why are tissues embedded?
Provides external support for the tissue so it can be cut into thin sections. Remember infiltration provided in processing gives the internal support.
What governs what medium is used for embedding?
Must use the same embedding medium as you used to infiltrate the tissue.
What is the most common medium for embedding?
Paraffin wax.
What temperature should the paraffin in the reservoir be?
The paraffin in the reservoir should be heated to 2 to 4degC higher than its melting point (specific to that wax type, i.e. soft or hard, etc.).
Note: I recall Jose said 1-2C above melting point for this. (Check notes)
What are the working areas of an embedding station?
Wax reservoir for the wax pellets to melt in.
Dispenser – for the wax to go from the reservoir to the mold
Control panel – to set temperatures of reservoir, tanks and warming plate. Can program to come on and shut off at certain hours.
Forceps warming block – spots to keep forceps or picks. These must be kept warm or they will stick to the specimens
Warm working areas – to place base mold and cassette while initially placing specimen in the mold
Cold working area – cools the paraffin in the base mold while gently pushing it in place – glues it where you need it to be.
Warming bath - to warm specimens up prior to embedding.
Storage area for molds – the molds must be kept warm. When you put a bit of wax in the bottom of the mold to “glue” your specimen in place it needs to be melted until you want it to harden slightly around your specimen.
Cold plate – area where the paraffin can cool down and harden quickly
Waste wax drawer
Why must the specimens be placed in a warming bath prior to embedding?
The wax in the tissue must be in a liquid state while you are embedding or it will break out of the block.
Should you open more than one cassette at a time at the embedding station?
No, this could result in a possibility of sample mix-up. Which could lead to misdiagnosis!
What are some guidelines for the embedding procedure to follow?
- Make sure the tissue cassette and base mold are kept warm until you have the specimen oriented
- Check the side of the cassette for indication of multiple specimens (and the number if there are multiple – must match what you have).
- Open the cassette on the warming plate. Check the lid of the cassette for any tissue before discarding it
- Use warmed forceps to move the tissue around.
- Place tissue in center of mold with slight angle.
- Push specimen down to base of mold evenly, gently with flattest part on base of mold and make sure it is held flat.
- Slide mold onto cold section while holding tissue position in mold. Don’t let go or tissue will float up.
- Don’t put tissue back on hot plate.
- Place cassette on top of mold, label towards RHS.
- Fill up again with wax, avoid bubbles. Extend wax past cassette perforations.
- Place on cold plate for rapid cooling.
What is important to remember after you have placed your specimen on the cold plate?
Once the specimen is oriented, make sure you do not put the mold back down in a warm area – will melt the wax and the tissue will raise up
Which direction should the cassette be placed when returning it to the top of the mold?
Always have the labeled part of the cassette on the right hand side.
Once you get the cassette on top of the mold how far do you top up with wax?
You need to extend past the cassette perforations to add support while cutting. (Otherwise the block could fall off while cutting).
How should the tissue be oriented in the mold?
Piece of tissue must be in the center of the mold.
Slight angle helps with cutting.
What ever is in the bottom of the mold (towards you) will be at the top of the block when cutting (and last to hit the blade).
Keep tissue as flat as possible in the bottom of the mold, evenly pushed out.
Must have wax surrounding tissue, if not must use a bigger mold. Note: Jose says you need about 2-3 mm of wax surrounding the tissue. Although I recall you could be closer in direction but not both.
How are tubular structures cut and orientated?
Cut transversely (cross section) to see all layers Small and large intestine, gall bladder, and trachea are tubular structures but you will only have a piece of it (not the entire tube) – Tissues with a wall - These must be oriented to see all the layers.
Which tissues are tubular and also small enough to have an entire tube on a slide?
Blood vessels, vas deferens, fallopian tubes, appendix, ureter, etc.
These are often small enough that you have the entire tube
How is skin to be orientated?
Skin:
Oriented to see all layers, must have hard dermal layer as the last part to hit the knife. This means while embedding have it closest to you. When it is removed from the mold and placed on the microtome it is at the top.
