Fixation Flashcards
_____________ is the use of physical and chemical methods, to prevent changes associated with tissue decay.
Fixation
State three physical methods of fixation.
Heating, freezing, and microwaving
Heating coagulates tissue ________.
Proteins
Freezing in _________ _________ or carbon dioxide causes water within the tissues to crystallise, forming a solid matrix.
Liquid nitrogen
Coagulants (such as acetone and alcohols), cross-linkers (such as formalin), and unclear (such as mercuric chloride) are all _________ fixation methods.
Chemical
Chemical methods use solutions to __________ tissues, ‘fixing’ all of the components in place.
Permeate
Cross-linkers, such as formaldehyde and glutaraldehyde, form ___________ bridges between side- and end-groups of proteins, creating a solid protein mesh, linked by methyl groups, in a protein-COO-CH2-HN-protein formation.
Methylene
Formaldehyde, or _________, is the fixative of choice in the majority of laboratories.
Formalin
In formalin, _________ _________ reacts with proteins in the sample to form methylene bridges.
Methylene glycol
Cytoplasmic streaming is a form of uneven staining, observed when carbohydrates are pushed to the sides of the subject tissue. It is often observed after __________ use.
Formalin
______________ offers the best morphological preservation.
Glutaraldehyde
State the chemical formula of glutaraldehyde.
CHO.(CH2)3.CHO
Ethanol, methanol, and acetone are examples of ___________.
Coagulants
What is the main disadvantage of coagulants?
They cause shrinkage, with poor preservation of mitochondria
Osmium tetroxide is an oxidising agent, and a secondary fixative, which turns black when fixing ________.
Lipids
A mixture of fixatives, buffers, and salts, which act together, to give best fixation of tissue, is a ____________ fixative.
Compound
List three compound fixatives.
Zenker’s, Carnony’s, and Bouin’s
True or false: compound fixatives may be responsible for over- and under-fixation, antigen masking, and fixation-related deposits.
True
Most tissues, with the exception of muscle biopsies for enzyme histochemistry, and skin and __________ biopsies for investigation of inflammatory skin conditions, are suitable candidates for fixation.
Mucosal
Preservation, or fixation, prevents ____________ and putrefaction of cells and tissues.
Autolysis
__________ refers to nuclear fading.
Karyolysis
Pyknosis is __________ shrinking.
Nuclear
______________ is nuclear fragmentation.
Karyorrhexis
Nuclear dissolution leads to an ______________ necrotic cell.
Anuclear
Give four characteristics of an ideal fixative.
Prevention of decomposition, enhancement of staining, preservation of tissue volumes, and non-toxicity
In a strong acid environment (low pH), the primary target groups on proteins become unreactive to ____________.
Formaldehyde
At low pH, the ____________ effects of formaldehyde are reduced.
Crosslinking
Time of fixation is equal to the __________ the fixative must penetrate.
Distance
Gross specimens should be ______________ in fixative, not saturated.
Suspended
Diffusion of molecules increases in _________ temperatures.
Raised
Formalin stronger than ___% causes hardening and shrinkage.
10
Ethanol weaker than ___% cause a lack of dehydration.
70
Best fixation results are obtained in a slightly ____________ solution.
Hypertonic
Hypotonic solutions cause _________.
Shrinkage
___________ solutions can cause swelling of tissue.
Hypertonic
In the case of CD20 marker analysis, a lack of a __________ positive stain indicates poor fixation.
Brown
Decalcification is performed on _______ samples.
Bone
