Located at each end of the esophagus is a ringlike band of muscle fibers, termed a sphincter. Usually the upper and lower esophageal sphincters are constricted, preventing continual entry of air into the esophagus or the leakage of stomach contents into the tract. The sphincters relax during swallowing, however, to facilitate the passage of food. Many individuals also experience relaxation or incomplete constriction of the lower esophageal sphincter at other times, resulting in acid reflux. The burning related to this abnormal entry of stomach acid into the esophagus is commonly called heartburn.

In the digital image above, a rat esophagus tissue section is presented that was labeled with the fluorophore Oregon Green 488 conjugated to wheat germ agglutinin, a fluorescent lectin that selectively binds to sialic acid residues. Wheat germ agglutinin conjugates are often used as probes for the Golgi network in mammalian tissues and cells. The sample was also stained with Alexa Fluor 568 conjugated to phalloidin and Hoechst 33342, which target the cytoskeletal filamentous actin network and nuclear DNA, respectively. 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.