Rectum

Overview

The rectum is the final portion of the large intestine and serves as a temporary storage site for feces before defecation. It is a muscular, tubular structure that connects the sigmoid colon to the anal canal. Though part of the digestive tract, the rectum also plays a role in continence and sensory feedback during the defecation process.

Location

The rectum is located in the pelvic cavity. It:

• Begins at the level of the S3 vertebra (continuation of the sigmoid colon)

• Terminates at the anorectal junction, about 2–3 cm above the anal verge

• Is situated posterior to the bladder in males and posterior to the vagina and uterus in females

• Lies anterior to the sacrum and coccyx

Structure

The rectum is approximately 12–15 cm long and consists of:

• Upper third: Covered by peritoneum anteriorly and laterally

• Middle third: Covered by peritoneum only on the anterior surface

• Lower third: Located below the peritoneal reflection and entirely extraperitoneal

Internally, the rectum has:

• Transverse rectal folds (valves of Houston): Three semilunar mucosal folds that help support fecal mass

• Muscularis externa: Thick longitudinal and circular muscle layers that aid in peristalsis and continence

• Mucosa: Lined with columnar epithelium that transitions to squamous epithelium at the anal canal

Function

The rectum plays critical roles in:

• Temporary fecal storage: Holds feces until voluntary elimination is appropriate

• Defecation reflex: Triggers rectal contraction and internal anal sphincter relaxation when filled

• Coordination with pelvic floor muscles: Works with the levator ani and anal sphincters to allow or delay defecation

Physiological Role(s)

The rectum contributes to digestive physiology and continence through:

• Sensory detection: Detects stretch from fecal accumulation, signaling the need to defecate

• Pressure modulation: Helps regulate intra-abdominal pressure during bowel movements

• Continence preservation: Maintains fecal continence in collaboration with the internal and external anal sphincters

• Neural regulation: Governed by autonomic (parasympathetic via pelvic splanchnic nerves) and somatic innervation (pudendal nerve)

Clinical Significance

The rectum is involved in numerous clinical conditions and is a common site for examination and procedures:

• Rectal cancer: A common malignancy, especially in older adults; evaluated by colonoscopy and treated via surgery, radiation, or chemotherapy

• Hemorrhoids: Dilated veins in the rectal or anal region; internal hemorrhoids are typically painless but may bleed

• Rectal prolapse: Full-thickness protrusion of the rectal wall through the anus; common in older adults and chronic straining

• Fecal incontinence: Loss of voluntary bowel control due to sphincter damage, nerve injury, or severe constipation

• Rectal examination: Digital rectal exam (DRE) is essential in assessing prostate size, rectal masses, and sphincter tone

• Ulcerative colitis: Inflammatory bowel disease that almost always starts in the rectum (proctitis)

• Rectocele: Herniation of the rectum into the vaginal wall, typically due to pelvic floor weakness

The rectum’s anatomical position and unique role in both digestion and defecation make it a critical focus in colorectal surgery, gastroenterology, and pelvic floor medicine.