STAINING
PREPARED BY MR. ABHIJIT DAS
Staining in pathology is a method used to color cells and tissues so they
can be seen clearly under a microscope.
TYPES OF DYE
Hematoxylin
– Stains cell nuclei blue or purple.
Eosin – Stains cell components like the cytoplasm pink.
Gram stain
– Differentiates between bacteria types (Gram-positive
and Gram-negative).
Giemsa stain
– Used for blood cells and parasites, staining
them pink or purple.
Periodic Acid-Schiff (PAS)
– Stains carbohydrates and mucus magenta.
Toluidine blue
– Highlights certain tissue structures, staining
them blue.
MECHANISM OF STAINING
Affinity: Dyes bind to
cellular structures based on attraction between opposite charges. For example, basic dyes like Hematoxylin bind
to acidic structures (e.g., DNA in the nucleus),
staining them blue/purple. Acidic dyes like Eosin bind to basic components
(e.g., proteins in the cytoplasm), staining them pink.
Permeability:
Stains penetrate cells and tissues depending on their size and composition. For example,
Gram stain differentiates bacteria based on their cell wall permeability,
coloring Gram-positive bacteria purple and Gram-negative pink.
FACRORS INFLUENCING STAINING
pH: The acidity or alkalinity of the stain affects how it binds to different cell parts.
Temperature:
Warmer temperatures can speed up the staining
process.
Concentration:
Stronger stains can produce more intense colors.
Time: The longer a sample is stained, the darker the color will be.
Tissue Permeability:
How easily a stain enters the tissue depends on the thickness of
the cells.
METACHROMASIA
Metachromasia is a phenomenon where a dye changes color after binding to certain cell
parts.
For example, a blue dye like
Toluidine Blue might turn purple or red when it attaches to specific tissues (Ex-
Cartilage).
MORDANT
A mordant is a substance used in staining to help dyes bind more strongly to tissues or cells.
ACCENTUATORS
Accentuators are substances used in staining to enhance the color of a dye. They help improve the
contrast and visibility of specific structures in tissues or cells.