The primary function of the rectum is to temporarily store waste material prior to defecation. As undigested food builds up in the rectum, the muscular rectal walls expand. This expansion produces pressure that triggers the urge to expel fecal material. Eventually the pressure leads to the relaxation of the anal sphincter, allowing the material to be voided from the body via peristalsis. As this occurs, the rectum shortens.

The sample of rat rectum tissue featured in the digital image above was labeled with Texas Red conjugated to wheat germ agglutinin, a lectin that selectively binds to sialic acid residues found in both mucoproteins and glycoproteins. The cells were also stained with Alexa Fluor 488 conjugated to phalloidin and the dye 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.