ANATOMY OF THE LARGE INTESTINE

ANATOMY OF THE LARGE INTESTINE

The large intestine begins at the ileocaecal valve and extends to the anus. It is divided into the caecum, ascending colon, hepatic flexure, transverse colon with attached greater omen tum, splenic flexure, descending colon, sigmoid colon and rectum. The large intestine is approximately 1.5 /uni00A0 m long, but it can be concertinaed over an endoscope so the caecum can be reached with 70–90 /uni00A0 cm of a colonoscope. The external appearance of the colon is distinguished from the small bowel by the presence of taenia coli, three bands of longitudinal muscle that run from the appendix base to the rectosigmoid junction and fat-filled peritoneal tags known as appendices epiploicae found principally on the left side of the colon. The taenia coli act to pull the colon into its sacculated sta te, producing a series of haustrations that may be visible on abdominal radiograph and allowing distinction from distended small intestine, which has complete transverse markings caused by the valvulae conniventes (see Chapter 74 ). The important posterior relations of the caecum and ascending colon are the right ureter, right gonadal vessels and duodenum and these must be protected at surgery . The left ureter, left gonadal ves sels and tail of the pancreas must be protected when operating on the left colon. The blood supply of the large intestine from the caecum to the distal transverse colon is derived from branches of the superior mesenteric artery and from the inferior mesenteric artery and its branches more distally . The middle colic artery is a prominent branch of the superior mesenteric arter y arising soon after the origin, which divides almost immediately into Valvulae conniventes describes a fold of mucous membrane that passes across two-thirds of the bowel circumference. Sir David Drummond , 1852–1932, born Dublin, Ireland, pathologist and physician at the Royal Victoria Infirmary , Newcastle (1878–1920), President of the British Medical Association (1921–1922) and vice chancellor of Durham University (1920–1922). two or three large arcades to supply the transverse colon. The precise vascular anatomy is variable and needs to be taken into account when performing colectomy , particularly total meso - colic excision for cancer (see Chapter 65 ). Peripheral branches of the superior and inferior mesenteric vessels usually anasto - - mose, resulting in a continuous vascular supply along the colon, referred to as the marginal artery of Drummond. This vessel is often the key b lood supply to the vascular arcades, ensuring adequate perfusion of a colonic anastomosis; however, blood flow in the ‘watershed’ area of the splenic flexure representing the junction of the embryological mid- and hindgut may be tenuous. Sudden occlusion of the inferior mesenteric artery may leave the area of the splenic flexure poorly perfused, lead - ing to an ischaemic colitis. V enous and lymphatic drainage of the colon follows the arterial supply and venous drainage is into the portal system. High ligation of the artery supplying a segment of colon will therefor e also remove the lymphatic vessels and nodes, a key technical point in cancer surgery . The nerve supply to the large intestine is derived from the splanch - nic nerves via sympathetic plexuses surrounding the superior (midgut) and inferior (hindgut) mesenteric arteries. Visceral pain from the part of the colon supplied by the superior mes - - enteric arter y is thus felt, like that of the small intestine, in the periumbilical region, while pain from the colon distal to that point is felt suprapubically .

The importance of non-surgical management of large • The principles of colonic surgery • That complex intestinal problems are best managed by a • The management of acute surgical problems of the large •