Rectum: Function, Anatomy and Common Diseases
The rectum is the final section of the large intestine, responsible for storing and controlling the elimination of stool from the body.
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The rectum is the final section of the large intestine, responsible for storing and controlling the elimination of stool from the body.
What Is the Rectum?
The rectum is the last segment of the large intestine (colon). It connects the sigmoid colon to the anal canal and measures approximately 12 to 16 centimeters in length. Located in the pelvis, just in front of the sacrum, the rectum plays a critical role in bowel continence and the controlled passage of stool. It acts as a temporary reservoir for feces before defecation occurs.
Anatomy and Structure
Like the rest of the large intestine, the wall of the rectum consists of several layers: the mucosa (inner lining), submucosa, muscular layer (muscularis propria), and an outer covering. Inside the rectum, there are characteristic crescent-shaped folds of mucosa known as the transverse folds of the rectum (Houston valves). These folds help to support the contents of the rectum and regulate stool flow.
At its lower end, the rectum transitions into the anal canal, which is kept closed by the internal and external anal sphincter muscles. This sphincter system is responsible for maintaining continence -- the voluntary control of bowel movements.
Functions of the Rectum
The rectum serves several essential functions within the digestive system:
- Stool storage: The rectum receives and temporarily stores fecal matter from the sigmoid colon until voluntary defecation is convenient.
- Defecation reflex: As the rectum fills with stool, stretch receptors in its wall are activated. These send signals to the brain, triggering the urge to defecate.
- Coordinated emptying: During defecation, the sphincter muscles relax while the rectal muscles contract, expelling stool through the anal canal.
- Water absorption: Small amounts of water and electrolytes are still absorbed in the rectum before stool is excreted.
Common Diseases of the Rectum
Rectal Cancer
Rectal cancer is a malignant tumor arising from the lining of the rectum. Together with colon cancer, it is classified as colorectal cancer, one of the most common cancers worldwide. Warning signs include blood in the stool, changes in bowel habits, and unexplained weight loss. Regular screening, particularly colonoscopy, is key to early detection and improved outcomes.
Hemorrhoids
Hemorrhoids are enlarged blood vessels in and around the anal canal and lower rectum. They are extremely common and may cause itching, burning, rectal bleeding, and discomfort. Treatment ranges from conservative measures -- such as a high-fiber diet and sitz baths -- to minimally invasive or surgical procedures, depending on severity.
Rectal Prolapse
A rectal prolapse occurs when part or all of the rectal wall protrudes through the anus. This can lead to fecal incontinence, pain, and mucus discharge. Surgical correction is often required to restore normal anatomy and function.
Proctitis
Proctitis refers to inflammation of the rectal mucosa. It can be caused by inflammatory bowel diseases such as Crohn's disease or ulcerative colitis, infections, or radiation therapy. Symptoms include bloody or mucus-containing stools, rectal pain, and frequent urges to defecate.
Fecal Incontinence
Fecal incontinence is the inability to control bowel movements, leading to unexpected leakage of stool. Causes include sphincter muscle damage, neurological disorders, and pelvic floor weakness. Treatment options include pelvic floor exercises, biofeedback therapy, and in severe cases, surgical intervention.
Diagnostic Methods
Several methods are used to examine the rectum:
- Digital rectal examination (DRE): A physician manually palpates the inside of the rectum to detect abnormalities such as masses or polyps.
- Proctoscopy and rectoscopy: These procedures use rigid or flexible instruments to directly visualize the interior of the rectum.
- Colonoscopy: A full endoscopic examination of the entire large intestine, including the rectum, used for cancer screening and diagnosis.
- Pelvic MRI: Magnetic resonance imaging provides detailed images of the rectum and surrounding structures, especially important for staging rectal cancer and planning treatment.
- Endorectal ultrasound: Transrectal ultrasonography is used to assess the layers of the rectal wall and nearby lymph nodes.
Prevention and Bowel Health
A balanced diet rich in dietary fiber, regular physical activity, and adequate hydration all contribute to healthy rectal and bowel function. Health authorities recommend regular colorectal cancer screening from the age of 45 to 50, or earlier for individuals with increased risk factors such as a family history of colorectal cancer.
References
- World Health Organization (WHO): Colorectal Cancer Fact Sheet. www.who.int (accessed 2024).
- American Cancer Society: Colorectal Cancer Early Detection, Diagnosis, and Staging. www.cancer.org (accessed 2024).
- Standring, S. (Ed.) (2021): Gray's Anatomy -- The Anatomical Basis of Clinical Practice. 42nd Edition. Elsevier.
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