L.1 Preservation & Processing Flashcards
Why do samples need to be preserved and fixed?
To prevent tissue death and maintain viability
As soon as tissues are removed from the body, the vascular supply is lost, haemoglobin leaches from the red blood cells and tissues begin to die.
What does fixation do to tissue?
Hardens tissue and converts it to an irreversible semi-solid gel
Fixation allows easy manipulation of soft tissue.
What are preservatives used for?
- Support cells with nutrients
- Maintain viability
- Conserve constituents
Preservatives are supplemented media that help in various applications.
What media does flow cytometry use?
RPMI
Flow cytometry utilizes RPMI as a preservative.
What media is used for cell and tissue culture?
Supplemented growth media
This media supports the growth and maintenance of cells and tissues.
What is the difference between a preservative and a fixative?
A preservative maintains tissue without degradation; a fixative prevents protein breakdown and stabilizes proteins
A fixative retains a semblance of the tissue’s life-like state.
What are the aims of fixation?
- Prevent autolysis and putrefaction
- Maintain tissue close to living state
- Maintain shape and volume
- Allow subsequent staining
Fixation is crucial for accurate tissue analysis.
What types of analysis depend on the type of fixative?
- Morphology
- IHC (Immunohistochemistry)
- Histochemistry
The type of sample (Cytology/Histology) also influences the choice of fixative.
What are the two methods of fixation?
- Thermal (heat or freezing)
- Chemical (crosslinking or coagulation)
Different methods are used based on the requirements of the analysis.
Fill in the blank: A _______ prevents autolysis and putrefaction.
fixative
Fixatives are essential in preserving the integrity of tissue samples.
True or False: A fixative is used to maintain tissue viability over long periods.
False
That is the role of a preservative, while a fixative stabilizes proteins.
What is thermal fixation?
Heating and freezing processes that coagulate proteins and create a solid matrix.
Heating can be done via Microwave or Boiling, while freezing can involve Liquid nitrogen or CO2.
What are the applications of thermal fixation?
Used for storage of fresh or pre-fixed cells and tissues, including:
* Biobanking
* Molecular studies
* Cell lines
* Research
* Frozen sections for excision margins
What is chemical fixation?
The process where chemical solutions permeate cells and tissue structures to preserve them.
What is a crosslinking fixative?
A type of fixative that forms methylene bridges between protein groups, creating a solid protein mesh.
Examples include Formaldehyde and Glutaraldehyde.
What is a coagulant fixative?
A fixative that coagulates proteins and alters their tertiary structure, penetrating rapidly and causing shrinkage.
Examples include ethanol, methanol, and acetic acid.
True or False: Formaldehyde is the most commonly used routine fixative in laboratories.
True
What is the concentration of formaldehyde in 10% formalin?
4% formaldehyde
How long does formaldehyde take to fix small and large samples?
Small samples in a few hours; larger specimens overnight.
What are the properties of Glutaraldehyde?
Provides best morphological preservation but is suitable for small fragments only.
Used in electron microscopy and typically found in a 2.5% buffer solution.
What is the role of osmium tetroxide in fixation?
Acts as a secondary fixative in Electron Microscopy and turns black when fixing lipids.
What does mercuric chloride do in tissue fixation?
Precipitates proteins, providing good staining quality and hardening tissue.
What is picric acid used for in fixation?
A good fixative for glycogen but is potentially explosive.
What are dichromate fixatives used for?
Used as a secondary fixative; potassium dichromate is used when chromaffin reaction is required.
