Surgery of colon and rectum is done for various reasons including cancer, diverticulitis, inflammatory bowel disease, volvulus and fistulae.

Anatomy and Physiology

• The large bowel absorbs 90% of the water content of the digested food it receives from the small intestine.
  
• It also propels the residue towards the rectum, where it is stored and expelled with a bowel movement
  
• The large bowel is composed of:
  
  1. Colon. The colon averages 150 cms. (60 inches) in length. The colon is divided into four segments: the ascending colon, transverse colon, descending colon and sigmoid colon. There are two bends (flexures) in the colon. The hepatic flexure is where the ascending colon joins the transverse colon. The splenic flexure is where the transverse colon merges into the descending colon. (Figure 1)
     
  2. Cecum. This is the first portion of the large bowel and is joined to the small bowel. The appendix lies at the lowest portion of the cecum. (see Appendectomy)
     
  3. The ascending colon is about eight inches in length, extends upwards from the cecum to the hepatic flexure near the liver
     
  4. The transverse colon is usually over 18 inches in length and extends across the upper abdomen to the splenic flexure
     
  5. The descending colon, usually less than 12 inches long extends from the splenic flexure downwards to the start of the pelvis
     
  6. The sigmoid colon, which is S-shaped and measures about 18 inches long. It extends from the descending colon to the rectum
     
• Rectum. The rectum is a curved pouch that lies in the hollow formed by the sacrum and connects with the anal canal at its lower end.
  
• The wall of the colon is composed of four layers (Figure 2):
  
  1. Mucosa - The epithelial (single layer of cells) lining is flat and regenerates itself every 3-8 days. Small glands lie beneath the surface
     
  2. Submucosa - The area between the mucosa and circular muscle layer and is separated from the mucosa by a thin layer of muscle, the muscularis mucosa
     
  3. Muscularis propria - The inner circular and outer longitudinal muscle layers
     
  4. Serosa - The outer single cell thick covering of the bowel. Similar to the peritoneum, the layer of cells that lines the abdomen
     
• The colon does not have lymphatic channels in the submucosa between the mucosa and muscle. This is important because tumors invading into this area do not have lymphatic channels to metastasize (spread) through

Figure 1 - Anatomy of the colon.	Figure 2 - Cross-section through the wall of the colon (see text). © C. Hogan