FIXATION Flashcards
The specimen is placed in a liquid fixing agent (fixative) such as ________
FORMALDEHYDE (FORMALIN)
It is usually as a phosphate-buffered solution, is the most popular fixative
for preserving tissues that will be processed for paraffin embedding.
FORMALIN
The critical step in the preparation of histological sections is ______
FIXATION
Following fixation, appropriately trimmed specimens are placed in
suitable ___________ to segregate them from
other specimens.
LABELLED CASSETTES (SMALL PERFORATED BASKETS)
Formalin-fixed, paraffin-embedded tissues may be stored indefinitely at ________, and nucleic acids (both DNA and RNA) may
be recovered from them decades after fixation.
ROOM TEMPERATURE
A process that preserves tissues from decay, thereby preventing autolysis or putrefaction
FIXATION
T/F
Fixation should be carried out as soon as possible after removal of the
tissues (in the case of surgical pathology) or soon after death (in the case of
autopsy) to prevent autolysis.
TRUE
T/F
Fixation terminates any ongoing biochemical
reactions, and may also increase the mechanical strength or stability of the
treated tissues.
TRUE
T/F
The fixatives employed prevent autolysis by inactivating lysosomal enzymes. They stabilize the fine structure, both inside and between cells, by making macromolecules resistant to dissolution by water and other liquids.
TRUE
T/F
Fixatives also inhibit the growth of bacteria and molds that give rise to putrefactive changes.
TRUE
T/F
Fixation prevents
degeneration, decomposition, putrefaction, and distortion of tissues after removal from the body.
TRUE
______ results from tissue digestion by intracellular enzymes that are released
when organelle membranes rupture.
AUTOLYSIS
Bacterial decomposition or ________ is brought about by microorganisms which may already be present in the specimen.
PUTREFACTION
________ methods include heating, microwaving and cryo-preservation (freeze drying).
PHYSICAL
______ fixation is rarely used on tissue specimens, its application being confined to smears of microorganisms.
HEAT
It is regarded as a form of heat fixation, is now widely practiced in routine laboratories
MICROWAVE FIXATION
________, usually in the form of freeze drying, has some applications in histochemistry but is not usually applied to diagnostic tissue specimens.
CRYOPRESERVATION
_______ fixation is usually achieved by immersing the specimen in the fixative solution (immersion fixation) or, in the case of small animals or some
whole organs such as a lung, by perfusing or injecting the vascular system with fixative (perfusion fixation).
CHEMICAL
VAPOR TYPE FIXATIVES are ______, which is used to vapor-fix freeze-dried tissues
PARAFORMALDEHYDE & OSMIUM TETROXIDE
_________ whereby the chemical constituent of the fixative is taken in and becomes part of the tissue by forming cross-links or
molecular complexes and giving stability to the protein.
ADDITIVE FIXATION
EXAMPLES OF ADDITIVE FIXATION
FORMALIN, MERCURY, & OSMIUM TETROXIDE
________ whereby the fixing agent is not incorporated
into the tissue, but alters the tissue composition and stabilizes the tissue
by removing the bound water attached to H-bonds of certain groups
within the protein molecule.
NON-ADDITIVE FIXATION
Fixative solutions may contain a single fixative agent dissolved in a solvent
such as _______ or _______ or more commonly, a buffer solution to stabilize pH.
WATER or ALCOHOL
Specimens should be transferred to fixative quickly _______ after
surgery as deterioration will commence with the loss of blood supply.
LESS THAN 1 HOUR
Tissues should be fixed in a sufficient volume of solution; generally in a
ratio of ____ or at least ____ fixative to specimen, for penetration to occur
in the most efficient manner.
20:1 or at least 10:1
Anatomical barriers to fixation must be _______ or _______ (e.g. fascia,
bone, feces, thick tissue)
REMOVED or INCISED
large specimens must be ______ or ______ with fixative (e.g. lung) or opened and cleaned (gastrointestinal
tract) to allow penetration.
SECTIONED or INFLATED
The volume of fixative is important. Traditionally, the amount of fixative used has been ______ the volume of tissue to be fixed.
10-20 times
Fixation is best carried out close to _______ pH, in the range of ______
NEUTRAL pH (6-8)
Commercial formalin is buffered with phosphate at a _______
pH of 7
Many laboratories use tissue processors that work at ______ for regular tissue processing.
40C
For electron microscopy and some histochemistry, the ideal temperature is ______
0-4C
Formalin heated to ____ is sometimes used for the
rapid fixation of very urgent biopsy specimens, although the risk of tissue
distortion is increased.
60C
Electron Microscopy tissue blocks size should be ______
1-2mm^2
Light Microscopy tissue blocks size should be ______
2cm^2 wide
Brain is usually suspended whole in _________ to ensure fixation and some hardening prior to sectioning.
10% buffered formalin for 2-3 weeks
For solid material (e.g., liver) the longest dimension should not exceed ______
10-15mm
HYPERTONIC = _______
SHRINKS
HYPOTONIC = ________
SWELL & BURST
