Rectum
The rectum is a crucial part of the gastrointestinal tract, situated at the end between the sigmoid colon and the anal canal, measuring approximately six inches (fifteen centimeters) in length. It functions primarily as a storage pouch for waste until defecation. The rectum is lined with mucous glands and has three lateral folds known as Houston's valves, which help retain feces until the body is ready to expel them. When the walls of the rectum stretch due to accumulating waste, nerve receptors signal the urge to defecate, leading to a series of muscular contractions that move the feces into the anal canal.
Various disorders can affect the rectum, including infections that may lead to abscesses or fistulas. Conditions such as rectal prolapse can occur when the rectum protrudes through the anus, often due to excessive straining. Inflammation of the rectal lining, known as proctitis, can arise from infections or other diseases. Moreover, the rectum is a common site for colorectal cancers, which primarily appear as adenocarcinomas. Early detection and surgical intervention can lead to a high survival rate, especially when the cancer is localized. Understanding the structure and function of the rectum is essential for recognizing its role in digestive health and potential medical issues.
Subject Terms
Rectum
Anatomy or system affected: Anus, gastrointestinal system, intestines
Definition: The pouch at the end of the gastrointestinal tract that collects and stores food wastes just before defecation.
Structure and Functions
The rectum is the pouch at the end of the gastrointestinal tract, between the sigmoid colon and the anal canal. It is about six inches (fifteen centimeters) in length, dilated slightly at the end (the rectal ampulla), and lined by an orange-red tissue with mucous glands, much like the colon.
The rectum remains empty until just before defecation when wastes pass into it from the colon. Three lateral folds in the rectum, called Houston’s valves, hold the feces in place until a sufficient quantity is collected and the walls of the rectum are distended. Nerve receptors in the walls detect the stretching and prompt the urge to defecate. Waves of muscular contraction, known as peristaltic waves, move the feces into the anal canal and through the anus.
Defecation depends in part on a person’s conscious relaxation of the anus in response to the defecation urge. If the urge is resisted, then the feces may return to the colon, where water may be absorbed from them. If defecation is postponed repeatedly, the feces may harden and cause constipation.
Disorders and Diseases
Like the anus, the rectum is subject to various malformations caused by infection or injury. The rectum may develop an abscess—a cavity in its wall that is filled with pus—when bacteria infest a mucous gland. The abscess may open a channel, or fistula, to another part of the rectum, the anus, or an entirely different organ, such as the vagina; fistulas can also be the product of other diseases, such a diverticulitis or injury to the rectum. When the rectum is made to protrude through the anus and outside the body, usually from straining at stool, the condition is called rectal prolapse. Rectal prolapse also occurs during the labor and delivery of a baby. Proctitis is inflammation of the rectal lining from various infectious diseases, such as ulcerative colitis or a sexually transmitted disease.
About a quarter of colorectal cancers, the most common of the gastrointestinal tract, occur in the rectum, about equally in men and women. They are adenocarcinomas, growing in the lining of the rectum, and if untreated, often spread to the liver or, less commonly, to the lungs and bones. Rectal cancer usually grows slowly and can be surgically removed. When the cancer is localized, the five-year survival rate for colorectal cancer is over 90 percent.
Bibliography
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