BMS221 Histology L7: Extracellular Matrix and Special Stains

Flashcards covering the components, types, and specialized staining techniques for the extracellular matrix as discussed in the BMS221 Histology lecture.

Type I Collagen

Thick fibres of mature collagen found in the dermis and lung that stain well with acid dyes (eosinophilic) and are very widespread.

Type II Collagen

Thin fibre meshes found specifically in cartilage.

Type III Collagen (Reticulin)

A delicate supporting network found in the spleen, liver, lymph nodes, and early wounds; these fibres are argyrophilic.

Type IV Collagen

Collagen located in basement membranes that is associated with carbohydrates and is positive for both PAS and methenamine silver.

Lysyl oxidase

An enzyme that uses a $Cu$ cofactor to facilitate the crosslinking of elastin molecules.

Van Gieson stain

A trichrome stain consisting of Weigert’s haematoxylin for nuclei, picric acid as a small dye, and acid fuchsin as a larger dye that displaces picric acid in collagen.

Masson’s trichrome

A stain using Weigert’s haematoxylin, acid fuchsin, phosphotungstic acid (PTA) to displace fuchsin from collagen, and aniline blue (a larger dye) to stain collagen.

Verhoeff-van Gieson

A regressive staining technique where tissues are overstained with haematoxylin and oxidizing agents, then differentiated until elastin is the last to decolourise, and counterstained with Van Gieson.

Aldehyde-fuchsin stain

A method that oxidises disulphide links with potassium permanganate to create anions, followed by staining with basic fuchsin; it is superior for demonstrating fine elastin fibres.

Orcein

A natural dye derived from the lichen $Roccella \text{ } tinctoria$ used to stain elastin dark brown; it also identifies Hepatitis B surface antigens.

Autofluorescence

A property of elastin where it typically emits green light when excited over a broad range of wavelengths.

Multiphoton microscopy

A technique involving the simultaneous absorption of 2 photons with a wavelength of approximately $700 \text{ } nm$ ($IR$) to produce excitation and fluorescence at a very thin focal plane.

Gordon & Sweets’ method

A silver impregnation technique for reticulin where silver ions bind to fibres and are reduced by a reducing agent into black metallic silver.

Proteoglycans

Molecules consisting of a core protein covalently linked to glycosaminoglycans (GAGs) that attract cations and water to create a viscous gel with compressive resistance.

Glycosaminoglycans (GAGs)

Heteropolysaccharides, such as chondroitin sulphate or keratan sulphate, composed of repeating disaccharide units like glucosamine and glucuronic acid.

Mucins

Polypeptide cores with polysaccharide chains that vary from neutral to strongly acidic, serving functions in lubrication and protection.

Alcian blue

A cationic dye with strong bases that binds electrostatically to polyanionic mucins and proteoglycans; its binding can be adjusted by varying the pH.

Periodic acid-Schiff (PAS)

A reaction where periodic acid ($HIO_4$) oxidises carbohydrates (1,2 glycol groups) to di-aldehydes, which then reduce Schiff’s reagent to a magenta color.

Adhesive glycoproteins

Extracellular matrix proteins such as fibronectin and laminin that use receptors like integrins to mediate cell adhesion, migration, and signal transduction.

Birefringence

Also known as double refraction, this occurs when the refractive index depends upon the polarization of light, requiring polarized light for visualization.