The layered structure of the duodenum is similar to that of the stomach. Both feature an inner lining known as the mucosa, a supportive layer termed the submucosa, a muscular stratum, and an outer covering, or serosa. Brunner's glands, which secrete highly alkaline mucus, are located in the submucosa of the duodenum. This mucus modifies the pH of the chyme that passes into the duodenum, changing it from acidic to basic, and facilitates additional food breakdown. Specialized ducts enable the secretions of the Brunner’s glands to enter the lumen of the duodenum.

In order to localize a red fluorescent tag to filamentous actin in the sample of rat duodenum tissue presented in the digital image above, the specimen was labeled with Alexa Fluor 568 conjugated to phalloidin, a phallotoxin derived from the toxic death cap mushroom. Oregon Green 488 conjugated to the lectin wheat germ agglutinin, which selectively binds to N-acetylglucosamine and N-acetylneuraminic residues, was also applied to the tissue sample, as was the DNA probe Hoechst 33342. Images were recorded in grayscale with a 12-bit digital camera coupled to a Nikon Eclipse 80i microscope equipped with bandpass emission fluorescence filter optical blocks. During the processing stage, individual image channels were pseudocolored with RGB values corresponding to each of the fluorophore emission spectral profiles.