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Colon

German: Colon

1 Definition

The colon, the longest part of the large intestine, lies between the caecum and rectum.

2 Anatomy

The colon runs in a frame-like form from the right lower quadrant of the abdomen, starting out from the small intestine in convoluted fashion and is divided into four sections:

The transition from the ascending colon to the transverse colon is marked by a curvature flexura coli dextra. The curvature between the transverse colon and descending colon in the left half of the abdomen is accordingly named the left colic flexure flexura coli sinistra.

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While the ascending and descending sections of the colon lie retroperitoneally and each is fused to the fascia transversalis, the intraperitoneal transversal colon and sigmoidal section exhibit mesentery components and are therefore able to side against the posterior abdominal wall. The colon possesses haustration, which originate(s) from the projecting crossfolds, the plicae semilunares coli in the lumen.

2.1 Blood supply

The arterial supply of the ascending colon occurs via the arteria colica dextra. The transverse colon is mainly supplied by the arteria colica media, whereas the arteria colica sinistra is responsible for supplying the descending colon. The arteries are interconnected by anastomoses such that their supply areas overlap.

Venous drainage is achieved via the veins with matching names (vena colica dextra, vena colica media and vena colica sinistra).

2.2 Innervation

The sympathetic innervation of the colon is supplied through the plexus mesentericus superior, and from the flexura colica sinistra onwards by the plexus mesentericus inferior. The nerve fibres follow the supplying blood vessels here. The parasympathetic innervation occurs in the proximal part of the colon through the nervus vagus, in the distal part via branches of the nervi splanchnici pelvici. The indistinct transition of the parasympathetic innervation is marked by Cannon's point, which is located roughly in the last third of the transverse colon.

3 Histology

The wall structure of the colon largely matches those of the other colon sections. However, the colon exhibits no continuous longitudinal muscle layer, but rather three sections of taenia, which facilitate intraoperative identification of the colon. Alongside the colon hang sections of adipose tissue ( appendices epiploicae). The colon typically exhibits no villi (intestinal villi), but a large number of crypts and many goblet cells instead.

4 Function

In being part of the large intestine, the colon is involved in the absorption of water and electrolytes from the intestinal content and therefore involved in its thickening. The colon is densely populated with bacteria and can take up vitamin K synthesised by bacteria.

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