In rats and other vertebrates, the large intestine is comprised of the cecum, colon, and rectum. The terminal portion of the organ is the rectum, which extends from the sigmoid flexure (an S-shaped portion of the colon) to the anal canal. Compared to many other parts of the alimentary canal, the rectum, with a length of only about 5 inches in the adult human, is quite short. Thus it does not wind back in forth in the body as do the intestines, but stretches simply in a straight line toward the anal sphincter.

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.

Labeling Rectal Tissue with Fluorescent Probes Conjugated to Phallotoxins and Lectins - 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.

Rat Rectum Tissue Section Triple Stained for the Golgi Network, F-Actin, and Nuclei - The body temperature of infants and very young children is often taken through the rectum. This technique is typically employed because rectal temperature is closer to the temperature of the core of the body than oral or other temperature readings. The younger an individual is, the more important such accuracy becomes. Another advantage of rectal temperature is that it is easier to obtain from children to small to cooperate with having their temperature taken orally.

Rat Rectal Tissue Sample Labeled with Alexa Fluor 488, Texas Red, and Hoechst 33342 - Colorectal cancer is one of the most common types of cancer in the United States. Cancers of the rectum account for about 20 percent of all cases of colorectal cancer, making them much less prevalent than cancers of the colon. The vast majority of both types of cancer are adenocarcinomas, which originate in the epithelial cells of glandular tissue.

Visualizing Golgi Complexes and Filamentous Actin in Rectal Tissue - Early detection of colorectal cancers is very important because those discovered at an early stage have a much better chance of being cured. Detection is often delayed, however, because many cases do not produce palpable symptoms. If symptoms do develop, they often include blood in the stool, rectal bleeding, diarrhea, constipation, gas pains, bloating, stomach cramps, unexplained weight loss, fatigue, and vomiting.

Sialic Acid Residues, Filamentous Actin, and Nuclear DNA in a Rat Rectum Tissue Sample - For many years it was thought eating a diet high in fiber could help prevent cancers of the rectum and colon. More recently, however, some studies have cast a certain amount of doubt on this long-held belief. For instance, a study carried out by the National Cancer Institute found that individuals who previously developed colorectal polyps, which can develop into cancerous tumors, were not any less likely to develop them again if they consumed a diet high in fiber over the course of several years.

Rat Rectum Tissue Labeled with Oregon Green 488 - Regular exercise and the maintenance of a healthy body weight may be important for the health of the colon and the rectum. A study carried out in 1997 examined the risk for colorectal cancer among a group of female nurses and found that moderate exercise, such as a 60 minute walk, on a regular basis reduced the risk of developing the disease by about 50 percent. That same study further indicated that the nurses with the highest body mass indices were nearly twice as likely to develop colon cancer as those subjects with the lowest body mass indices.