Anatomical and physiological background

The human large intestine (colon) is a visceral organ that lies with loops and flexures in varying configurations around the abdomen. The length of the organ is 125–154 cm and its diameter is approximately 4.5 cm. The colon is functionally divided into two parts, the right and left colon. The right colon extends from the caecum and the ascending colon to the mid transverse colon, and the left colon from the mid transverse colon through the descending colon and sigmoid to the rectum.

The wall of the organ consists of four layers – the mucosa, submucosa, circular and longitudinal muscle layers and serosa. The thickness of the wall of the large intestine is relatively constant, h ≈ 0.4–0.5 mm. Cells lining the mucosa and submucosa resemble those found in the small intestine. However, they contain significantly greater numbers of goblet cells. They secrete viscous mucus into the lumen and thus moisturize and lubricate the passage of the waste. The layers play a major role in digestion and absorption of food, water and electrolytes. It is the absorption of fluids and bacterial processing that transform the intraluminal effluent into solid stool.

The longitudinal muscle is organized in three bands – teniae coli. They run from the caecum to the rectum, where they fuse together to form a uniform outer muscular layer. The circular muscle layer is homogeneous and uniformly covers the entire colon.