Tissue Processing and Embedding Flashcards
What are the 4 steps of tissue processing
fixation, dehydration, clearing, infiltration
What occurs during dehydration
removal of all unbound water and fixative
What occurs during clearing
removal of the dehydrating agent and provides a solvent for the paraffin wax
What occurs during infiltration
impregnation of the tissue with a support medium
What is the most common dehydrating agent
alcohol
Ethyl alcohol
routinely used, fast acting and non toxic but might cause hardening and shrinkage of tissues
Isopropyl alcohol
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
Methyl alcohol
similar to ethanol but more hazardous
What is one thing that a clearing agent must do
be soluble in both dehydrants and paraffin
Why must a clearing agent have a high refractive index
to make the tissue appear transparent when mounted on glass
Xylene
routinely used. fast acting and miscible with most solvents and paraffin. Over-exposure will harden tissue. Flamable and moderately toxic
Toluene
similar in action to xylene but unlikely to harden tissues. More volatile than xylene. Most often used in fibromuscular sampels
Chloroform
sometimes used for CNS specimens. Non-flammable but highly toxic, in the presence of oxygen may form phosgene which is exceptionally hazardous
Xylene substitute
less toxic and work almost as well as xylene. Short-chain aliphatic hydrocarbons. Intolerant of water and doesn’t harden tissues
What are universal solvents
capable of dehydrating and clearing tissue
What are the two most used universal solvents
tetrahydrofuran and dioxane
What is infiltration
forms the matrix that prevents distortion of tissue during microtomy
Paraffin wax
the most popular infiltrating and embedding media. non-toxic, inexpensive and easy to use
What are plasticizers used for
to make wax harder and facilitate ribboning
What is beeswax used for
lowers the melting point and makes the sections sticky
What is rubber used for
facilitates ribboning by increasing the elasticity
What are resins used for
makes the wax harder/increases the melting point
What does agitation do during tissue processing
ensures the solutions surrounding the tissue do not become locally saturated and helps avoid dead zones
What does heat do during tissue processing
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
