Histology Flashcards
(21 cards)
Define histology
Study of cells and tissues by microscopy
After sample of tissue has been taken, tissue fixation occurs. What is purpose of this?
- Prevents degradation of sample by preserving tissue
What causes degradation of sample?
- Stops autolysis (destruction of tissue by own enzymes)
Most common fixative?
Formalin (formaldehyde solution)
Only problem with formalin?
Poor nucleic acid preservation
After fixation, tissue is ‘cut up’ and ‘processed’. What is purpose of ‘processing’
To produce thin slice of tissue to examine under microscope
What must tissue be to be sliced thinly enough?
Stiff & resistant to mechanical trauma
What happens during ‘processing’
- Water removed from tissue by alcohol (dehydration)
- Alcohol replaced with xylene (clearing)
- Xylene replaced with paraffin wax
What is end result of processing?
Paraffin block: tissue embedded in wax
Why can’t tissue be placed straight in wax?
Tissue very rich in water and wax is hydrophobic
Why is frozen tissue not processed tissue used when looking at fats?
Processing removes any hydrophobic substances (i.e. fats)
A section is then taken of this wax block. Why are sections then stained?
Most cells are colourless so an unstained tissue section is translucent to light
What do acidic dyes react with?
Basic components in cells (i.e. acidophilic)
- e.g. proteins are basic
What do basic dyes react with?
Acidic components in cells (i.e. basophilic)
- e.g. nucleic acids are acidic (DNA/RNA)
What is most common stain?
H&E (Haematoxylin & Eosin)
What is H and what colour does it stain
Basic dye, stains acidic structures purple
What is E and what colour does it stain
Acidic dye, stains basic structures pink
What are results of Gram stain
- Gram -ve bacteria stain red
- Gram +ve bacteria stain blue
What is immunohistochemistry used for?
Used to detect specific protein targets
How does IHC differ from H&E?
It is not a tinctorial stain which are not specific
How does IHC work?
- Selectively identifying antigens (proteins) in cells
- Antibodies used as bind specifically to antigens
- Detected using colour change
