Large Intestine Structure and Characteristics

Carcinoma of the Stomach

• A common gastrointestinal malignancy
• Chronic gastric inflammation, pernicious anemia, and polyps predispose to its development
• Symptoms: vague epigastric pain, early fullness with eating, bleeding leading to chronic anemia, and obstruction
• Diagnosis: barium and conventional radiology, endoscopy with biopsy, ultrasound scanning for liver metastasis, and computed tomography for surgical resectability
• If diagnosed early, curative surgical resection is possible
• Overall 5-year survival rate: 5-20%, with a mean survival time of 5-8 months

Large Intestine

• Extends from the distal end of the ileum to the anus, approximately 1.5 m in adults
• Absorbs fluids and salts from the gut contents, forming feces
• Consists of:
  • Cecum
  • Appendix
  • Colon
  • Rectum
  • Anal canal
• Characteristics:
  • Large internal diameter compared to the small intestine
  • Peritoneal-covered accumulations of fat (the omental appendices)
  • Segregation of longitudinal muscle in its walls into three narrow bands (the taeniae coli)
  • Sacculations of the colon (the haustra of the colon)

Cecum

• The first part of the large intestine
• Inferior to the ileocecal opening and in the right iliac fossa
• Intraperitoneal structure due to its mobility
• Continuous with the ascending colon at the entrance of the ileum
• May cross the pelvic brim to lie in the true pelvis

Appendix

• A narrow, hollow, blind-ended tube connected to the cecum
• Large aggregations of lymphoid tissue in its walls
• Suspended from the terminal ileum by the mesoappendix
• Point of attachment to the cecum is consistent with the highly visible free taeniae leading directly to the base of the appendix
• Symptoms: fever, nausea, and vomiting
• Treatment: appendectomy

Colon

• Extends superiorly from the cecum
• Consists of the ascending, transverse, descending, and sigmoid colon
• Ascending and descending segments are (secondarily) retroperitoneal
• Transverse and sigmoid segments are intraperitoneal
• Right colic flexure: at the junction of the ascending and transverse colon
• Left colic flexure: at the junction of the transverse and descending colon

Rectum and Anal Canal

• The final segment of the colon begins above the pelvic inlet and extends to the level of vertebra SIII
• S-shaped structure, mobile except at its beginning and end
• Arterial supply:
  • Superior rectal artery from the inferior mesenteric artery
  • Middle rectal artery from the internal iliac artery
  • Inferior rectal artery from the internal pudendal artery (from the internal iliac artery)

Clinical Correlation

Congenital Disorders of the Gastrointestinal Tract

• Developmental anomalies can occur during gut development, many of which appear in the neonate or infant, and some of which are surgical emergencies
• Occasionally, such disorders are diagnosed only in adults

Malrotation and Midgut Volvulus

• Malrotation: incomplete rotation and fixation of the midgut after it has passed from the umbilical sac and returned to the abdominal coelom
• Proximal attachment of the small bowel mesentery begins at the suspensory muscle of duodenum (ligament of Treitz)
• Mesentery of the small bowel ends at the level of the ileocecal junction in the right lower quadrant
• Twisting of the small bowel around the axis of the superior mesenteric artery can lead to a reduction of blood flow and infarction

Bowel Obstruction

• A bowel obstruction can be either functional or due to a true obstruction
• Mechanical obstruction: caused by an intraluminal, mural, or extrinsic mass
• Functional obstruction: usually due to an inability of the bowel to peristalse, often due to a postsurgical state or abnormal electrolytes
• Signs and symptoms depend on the level of the obstruction and include central abdominal, intermittent, colicky pain, abdominal distention, vomiting, and absolute constipation

Diverticular Disease

• Development of multiple colonic diverticula, predominantly throughout the sigmoid colon
• Poor dietary fiber intake and obesity are linked to diverticular disease
• Presence of multiple diverticula does not necessarily require treatment
• Many patients have no other symptoms or signs