Taeniae coli

At a glance

English

Taeniae coli

Latin (TA2)

Taeniae coli

System

Digestive

Region

Abdomen

In order

From the free taenia to the omental taenia

About the taeniae coli

In most of the gut the outer muscle coat has a continuous longitudinal layer. In the large intestine this layer is gathered into three flat ribbons, the taeniae coli, each about a centimetre wide, lying just under the serous coat and easily seen through it. They run along the caecum and every part of the colon from ascending to sigmoid, and between them the wall has only a thin longitudinal layer. The three bands converge on the base of the vermiform appendix, which is the classic way to find the appendix at operation. At the junction of the sigmoid colon and rectum they spread out and fuse again, so the rectum has a complete outer longitudinal coat.

The bands are named by their relation to the peritoneal attachments of the colon. The mesocolic taenia lies where a mesentery would attach, the omental taenia where the greater omentum attaches on the transverse colon, and the free taenia lies away from both. On the caecum and the ascending, descending and sigmoid colon their positions are fixed: the free taenia faces forwards, the mesocolic taenia lies posteromedially and the omental taenia posterolaterally. On the transverse colon the gut is twisted, so the free taenia comes to face downwards, the mesocolic taenia backwards, at the attachment of the transverse mesocolon, and the omental taenia forwards and upwards, where the greater omentum joins.

Because the bands are shorter than the gut wall they lie on, they gather it into a row of sacculations, the haustra, separated by creases. These pouches, together with small fatty tags called omental appendices, distinguish the colon from the small intestine. The muscle receives parasympathetic fibres from the vagus in the proximal colon and from the pelvic splanchnic nerves (sacral segments) beyond, and sympathetic fibres that slow its activity.

The wall between the bands is weaker, especially where blood vessels pass through it. Under high pressure the mucosa can push out through these gaps to form diverticula, which are commonest in the sigmoid colon, where pressure is highest. Inflammation of these pouches is diverticulitis. Diverticula do not form in the rectum, where the longitudinal coat is complete again.

At operation the taeniae have practical uses beyond finding the appendix. They mark the colon at a glance, separating it from loops of small bowel, and they are strong enough to hold stitches well, so surgeons often place sutures along a taenia when joining or closing the colon. The haustra they create also give the colon its segmented outline on X-ray.