If the urge to expel fecal material from the rectum is not acted upon in a timely manner, the waste is often returned to the colon. The chief function of the colon is to remove water from waste. Thus, if material spends additional time in the colon, more water than normal is absorbed from the waste. The result can be very hard and dry stool that is difficult to pass through the anus. This condition is commonly known as constipation.

In order to localize a red fluorescent tag to F-actin in the sample of rat rectum 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.