Additive fixatives lead to the formation of which type of bridges in tissue?

• A. Methylene bridges
• B. Hydrogen bridges
• C. Ionic bridges
• D. Disulfide bridges

Answer: (A)

Additive fixatives stabilize tissue by forming covalent cross-links between protein molecules, specifically creating methylene bridges that link amino groups on neighboring proteins. Formaldehyde, a common additive fixative, reacts with amino groups to form a reactive hydroxymethyl intermediate, which then condenses with another amino group to produce a -CH2- bridging bond between proteins. This covalent cross-linking preserves the structural arrangement of cells and tissues, giving rigidity and stability during processing.

Hydrogen bonds are noncovalent and not the primary mechanism of fixation, so they don’t account for the strong, permanent cross-links produced by additive fixatives. Ionic bridges involve electrostatic interactions rather than covalent bonds. Disulfide bridges form between cysteine residues via S-S bonds and are not the characteristic cross-links generated by typical additive fixatives like formaldehyde.