The PAS reaction is used in histology to demonstrate which of the following tissue components?

• A. Polysaccharides, neutral mucins and basement membranes
• B. Proteins and lipids
• C. Nucleic acids
• D. Pigments

Answer: (A)

The PAS stain targets carbohydrate-rich substances in tissue. Periodic acid oxidizes sugar moieties to create aldehyde groups, which then react with Schiff reagent to yield a magenta color. This makes polysaccharides such as glycogen, neutral mucopolysaccharides in mucins, and the carbohydrate-rich components of basement membranes stand out prominently. It’s commonly used to visualize basement membranes and mucins because of their high carbohydrate content. If you want to distinguish glycogen specifically, you can treat sections with diastase before PAS; glycogen will be removed and the PAS staining will diminish, whereas other carbohydrate-containing structures may remain PAS-positive. In contrast, proteins, lipids, nucleic acids in typical histology contexts, and pigments do not produce the characteristic PAS-positive reaction.