The colon is a muscular tube-like component of the digestive system. Also commonly referred to as the large intestine, the colon extends from the small intestine to the anal opening and is about five feet long in a human adult. Six main sections comprise the mammalian colon: the cecum, ascending colon, transverse colon, descending colon, sigmoid colon, and rectum. Though there are some differences in the function of the colon in different species, the organ primarily acts as a temporary repository for waste products and as a site of water absorption. A few vitamins are also absorbed by the colon, though no digestive enzymes are present in the large intestine and most nutritive components of digested material have been removed by the time this part of the digestive system is reached.

A variety of bacteria are necessary for the colon to function properly, and antibiotic treatments can sometimes cause colon problems due to the elimination of such bacteria. Lack of sufficient dietary fiber has been linked to colon malfunction and disease as well, studies indicating that fiber is essential as food for the good bacteria that inhabit large intestine. Without enough fiber in the diet, the good bacteria are unable to survive, producing a void that can be inhabited by pathogens. Some of the many diseases that may affect the colon include colitis, Crohn’s disease, irritable bowel syndrome, polyposis, and cancer. Colon cancer is the second most commonly diagnosed cancer among Americans, but it has an excellent cure rate.

The sample of rat colon tissue presented in the digital image above was labeled with Texas Red conjugated to wheat germ agglutinin, a lectin that selectively binds N-acetylglucosamine and sialic acid residues. The specimen was also labeled with Alexa Fluor 488 conjugated to phalloidin and Hoechst 33342, targeting F-actin 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.

Rat Colon Tissue Labeled with Wheat Germ Agglutinin - The cellular composition of the colon epithelium is similar to that of the small intestine, but it contains a larger proportion of goblet cells interspersed among the columnar absorptive cells. In fact, the goblet cells of the colon are so large and abundant that the absorptive cells can be difficult to see. Goblet cells exhibit polarized morphology and a characteristic cup-like shape for which they are named.

Rat Colon Tissue Labeled with Wheat Germ Agglutinin Conjugated to Oregon Green 488 - The mucus present in the goblet cells of the colon is condensed, but when it is secreted, the material expands significantly. This process is very rapid. Studies indicate that mucus can increase 500 fold in volume in as little as 20 milliseconds. The expansion is indicative of a phase change that occurs as mucins move from secretory granules to the exterior of the cell via exocytosis.

Golgi Networks and F-Actin Visualized in a Rat Colon Sample - Colon cancer normally takes many years to develop, and many cases are believed to arise from adenomatous polyps. These polyps are glandular in origin. Because of their tendency toward malignancy, adenomatous polyps are usually removed when they are discovered. Colonoscopy, which involves the examination of the colon with a camera mounted on a flexible tube, is generally necessary to diagnose or rule out the presence of polyps or cancerous tumors.

Labeling Colon Tissue with Fluorescent Probes Conjugated to Phallotoxins and Lectins - Colon polyps and cancer are much more prevalent in industrialized western societies than other parts of the world. It is generally thought that the western diet, which tends to be low in fruits, vegetables, and roughage, is largely responsible. Smoking, drinking, obesity, and lack of exercise have also been associated with an increased risk of tumors and polyps in the colon.

Sialic Acid Residues, Filamentous Actin, and Nuclear DNA in a Rat Colon Tissue Sample - Symptoms of colon cancer may include a change in bowel activity or blood in the feces. Such blood is often invisible to the human eye, but can be detected through laboratory testing. Treatment for colon cancer is heavily dependent on the stage of the disease. Early stage tumors can often be removed with excision, and in some cases the cancer requires the removal of a significant portion of the colon. A colostomy may be necessary in such cases to provide an alternative route for waste removal from the body.