Histology Flashcards
What is the order of processes for preparing sections on slides?
Fixation, dehydration, embedding, cutting, mounting
What is the fixation (first step) used for?
To maintain tissue morphology and stabilise proteins
What do fixatives do?
Crosslink proteins and form gels
What do fixatives inhibit?
Bacterial/fungal growth
Degradation
What happens to soluble proteins?
Rendered insoluble which provides mechanical strength
What does fixation damage?
Proteins
What is the most common fixative?
Aldehydes
Explain aldehydes
Cross links are formed with and between protein molecules (e.g. lysine-argnine)
True or false: Reaction between protein and aldehydes is pH dependent
True (faster at high pH)
What are the problems with aldehydes?
Protein alterations that lead to change in isoelectric points
Toxic! Slow process!
Explain oxidising agents (fixative)
More detailed and higher resolution
Allows stable cross links
Explain microwave fixation and stabilisation
Fixation by heat which leads to good cross linking
Microwave energy reacts with dipolar molecules
Problems with microwave fixation and stailisation
Unsuitable for larger biopsies
What are the two types of embedding?
Paraffin embedding and frozen sections
Explain paraffin embedding
Cheap, simple and common
Lipid will be stripped out using paraffins and destroy enzyme activity and antigenic sites
Explain frozen sections
Used to demonstrate subcellular location of enzymes
Lipid analysis
Explain dehydration in tissue processing
Removal of aqueous fixative fluids
What is the most used dehydration agent?
Industrial methylated spirit
Explain clearing in tissue processing
Dehydrating agents do not generally mix with paraffin wax
Give tissue translucent appearance
Enable rapid removal of dehydrating agents
Which clearing agent is the best?
Xylene
What is the most used embedding agent?
Paraffin wax
When is paraffin wax not suitable?
When sections need to be thinner
Heat affects tissue (e.g. pancreas)
Processing agents remove or destroy tissue components
What are alternative embedding media?
Waxes - no longer used
Resins - high resolution, cut much thinner sections
Explain tissue orientation
Sections are generally cut from largest area of tissue
What are the exceptions to the general tissue orientation
Tubular structures
Skin and epithelial
Muscle biopsies
True or false: A microtome can cut frozen sections
False: it can’t
True or false: Sections are cut at 2-4 mM thick
False: cut at 2-4 um sections
True or false: Microtomes cannot cut through paraffin very easily
False: Cut easily
True or false: Citrus fruit oils mix well with alcohol
TRUE
