Which stain is used to demonstrate fat in tissue sections?

Study for the CAMLPR Histology Practice Test. Study with flashcards and multiple choice questions, each question has hints and explanations. Get ready for your exam!

Lipids in tissue are best visualized when a stain or fixative binds to them and creates a strong, contrasting deposit. Osmium tetroxide does this by reacting with the double bonds in unsaturated fatty acids, fixing and impregnating the lipid components to form osmiated, electron-dense (dark) deposits. This makes fat droplets and lipid-rich membranes stand out clearly in tissue sections and helps preserve lipids during processing, providing persistent contrast that is particularly useful in histology and electron microscopy contexts. While Sudan stains and Oil Red O are also used to demonstrate fat, they are typically applied in different preparation contexts (often frozen sections or specialized protocols) and do not offer the same fixation and permanence of lipid visualization that osmium tetroxide provides. Nile red is a fluorescent lipid stain and yields a different modality of visibility, whereas osmium tetroxide gives a robust, dark appearance of lipids in sections.