Tissue Prep and Staining Flashcards
What are the four steps of tissue preparation?
fixing, dehydration, removal of alcohol, embedding
What is fixing?
The addition of fixative (formalin) to reduce the deterioration of the tissue specimen. Acid fixatives preserve chromatin, nucleoli and spindle fibers. Basic fixatives preserve mitochondria.
What is dehydration?
Removal of water from the specimen by placing the tissue in ethanol. It however dissolves neutral fats.
What is clearing?
Removal of alcohol in the specimen and replacement with xylene, cedar oil or carbon tetrachloride.
What is embedding?
Placing the tissue specimen in several melted paraffin baths. All xylene is removed.
How are thin tissue slices prepared?
By using a sharp blade (rotary microtome), diamond knives.
How are animal tissues stained?
Paraffin is removed with xylene, xylene is removed with water, stain is applied and dehydrated with alcohol, alcohol removed via xylene.
H&E
hematoxylin and eosin; are used for routine staining and display strucutral features; NUCLEAR and CYTOPLASMIC components are dyed.
What are basic dyes?
Dyes that react with anionic groups of tissue components. (basophilic components). Methyl green, methylene blue, pyronine G, toluidine blue
What are acid dyes?
Dyes that bind to tissue components by forming linkages with cationic groups, such as amino groups of proteins. Acid fuchsin, EOsin
What is metachromasia?
A phenomenon whereby a dye changes color after reacting with a tissue component.
Histochemical techniques
Techniques used to study the chemistry of cells and tissues.
What are schiff reagent reactions?
Reaction dependent n the formation of aldehyde groups following exposure to HCl or periodic acid. Can react with deoxyribose to show DNA.
What are periodic acid-schiff reactions?
Reactions that cleave bonds between adjacent carbons of carbohydrates that form aldehyde groups. They form a deep-pinkish color; PAS-positive substances include glycogen (polysaccharides), glycoproteins and glycolipids.
RNA-rich organelles are stained with what kind of dyes?
basic dyes; e.g. toluidine blue and methylene blue.
