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Histotechnology > Tissue Processing and Embedding > Flashcards

Tissue Processing and Embedding Flashcards

1
Q

What are the 4 steps of tissue processing

A

fixation, dehydration, clearing, infiltration

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2
Q

What occurs during dehydration

A

removal of all unbound water and fixative

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3
Q

What occurs during clearing

A

removal of the dehydrating agent and provides a solvent for the paraffin wax

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4
Q

What occurs during infiltration

A

impregnation of the tissue with a support medium

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5
Q

What is the most common dehydrating agent

A

alcohol

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6
Q

Ethyl alcohol

A

routinely used, fast acting and non toxic but might cause hardening and shrinkage of tissues

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7
Q

Isopropyl alcohol

A

miscible with water but not miscible with salt solutions so tissue must be washed following fixation. Can mix with paraffin so clearing agent not always required. Non toxic and does not harden or shrink tissues

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8
Q

Methyl alcohol

A

similar to ethanol but more hazardous

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9
Q

What is one thing that a clearing agent must do

A

be soluble in both dehydrants and paraffin

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10
Q

Why must a clearing agent have a high refractive index

A

to make the tissue appear transparent when mounted on glass

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11
Q

Xylene

A

routinely used. fast acting and miscible with most solvents and paraffin. Over-exposure will harden tissue. Flamable and moderately toxic

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12
Q

Toluene

A

similar in action to xylene but unlikely to harden tissues. More volatile than xylene. Most often used in fibromuscular sampels

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13
Q

Chloroform

A

sometimes used for CNS specimens. Non-flammable but highly toxic, in the presence of oxygen may form phosgene which is exceptionally hazardous

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14
Q

Xylene substitute

A

less toxic and work almost as well as xylene. Short-chain aliphatic hydrocarbons. Intolerant of water and doesn’t harden tissues

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15
Q

What are universal solvents

A

capable of dehydrating and clearing tissue

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16
Q

What are the two most used universal solvents

A

tetrahydrofuran and dioxane

17
Q

What is infiltration

A

forms the matrix that prevents distortion of tissue during microtomy

18
Q

Paraffin wax

A

the most popular infiltrating and embedding media. non-toxic, inexpensive and easy to use

19
Q

What are plasticizers used for

A

to make wax harder and facilitate ribboning

20
Q

What is beeswax used for

A

lowers the melting point and makes the sections sticky

21
Q

What is rubber used for

A

facilitates ribboning by increasing the elasticity

22
Q

What are resins used for

A

makes the wax harder/increases the melting point

23
Q

What does agitation do during tissue processing

A

ensures the solutions surrounding the tissue do not become locally saturated and helps avoid dead zones

24
Q

What does heat do during tissue processing

A

heat will speed up the process though must be used with caution as using temperatures above 40C can effect the microscopic appearance of the tissue

25
Q

What does vacuum/pressure do during tissue processing

A

force solutions into tissues and open porous structures

26
Q

What does viscosity do during tissue processing

A

effects how quickly the stations are effective

27
Q

How does a modern day tissue processor work

A

tissue remains in a stationary retort and reagent solutions are pumped in and out according to the schedule

28
Q

What do microwave processors do

A

speed up processing by heating tissues from the inside which increased the diffusion of solutions. They are formalin and xylene-free

29
Q

What are the steps for xylene free processing

A
  1. fixation
  2. ethanol dehydration (50% ethanol)
  3. continued ethanol dehydration (80% ethanol, 20% isopropanol)
  4. isopropanol clearing (100% isopropanol)
  5. high temp paraffin wax infiltration
30
Q

What is a clean cycle

A

the removal of the paraffin from the retort and lines using xylene followed by alcohol

31
Q

What is the most common processing issue

A

incomplete dehydration

32
Q

What does over processing do to tissues

A

makes it brittle

33
Q

What is the most important part of embedding

A

orientation

34
Q

How to embed tissues with lumens

A

so that a cross section can be cut

35
Q

How to embed tissues with layers

A

on edge so that all layers are demonstrated

36
Q

How to embed cassettes with multiple pieces

A

side by side and oriented so the epithelium is facing the same way

37
Q

How to embed currettings

A

clustered centrally but not overlapping

38
Q

What are acrylic resins used for

A

to section undecalcified teeth, bones, or to cut thin sections <2um

39
Q

What are epoxy resins used for

A

electron microscopy

Histotechnology (10 decks)

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