MLT GlobeHistopathology: H&E and routine staining – page 3
45 Histopathology MCQs on H&E and routine staining with answers and explanations.
A tissue protein is placed in a staining solution at a pH equal to its isoelectric point. How will it behave?
At the isoelectric point the net charge is zero, so electrostatic binding of charged dyes is minimal. Below the IEP proteins are cationic and bind acidic dyes; above it they bind basic dyes.
Dye uptake by tissue in routine staining is best explained by:
Staining involves ionic and other chemical bonds together with physical factors such as adsorption, diffusion and tissue permeability. Neither mechanism alone explains most staining.
Which ionizable protein group, when negatively charged, helps tissues bind basic dyes?
Ionized carboxyl groups (–COO⁻) carry a negative charge and attract cationic dyes. Protonated amino groups (–NH3⁺) attract acidic dyes such as eosin.
Haematoxylin must be ripened to haematein. Which reagent can perform this chemical ripening?
Oxidizers such as sodium iodate, mercuric oxide or potassium permanganate convert haematoxylin to haematein. Aluminium salts are mordants.
Formalin-fixed tissue tends to stain more strongly with basic dyes than unfixed tissue. What causes this?
Formaldehyde binds and blocks basic amino groups, so the net charge of proteins becomes more negative and basophilia increases. Formalin contains no heavy metals.