Small & Large Intestine Abdomen, Pelvis & Perineum Unit Lecture 6 د. حيدر جليل الأعسم

Small Intestine: (Jejunum and Ileum) 6 m long. Upper 2/5 make up jejunum & lower 3/5 is ileum. Jejunum begins at DJ junction & ileum ends at ileocecal junc. Distinctive features, but a gradual change from one to other. They are freely mobile & are attached to post. abdominal wall by fan-shaped mesentery. Root of the mesentery permits entrance & exit of branches of superior mesenteric artery and vein, lymph vessels and nerves. Small intestine wall contains plicae circulares, which are larger, more numerous, and closely set in jejunum, While in the upper part of the ileum they are smaller and more widely separated and in the lower part they are absent.

Differences between jejunum & ileum Jejunum lies in upper part of peritoneal cavity below left side of transverse mesocolon; ileum is in lower part of cavity and in pelvis. Jejunum is wider bored, thicker walled, and redder than the ileum. Jejunal mesentery is attached to post. abdominal wall above and to left of aorta, whereas ileal mesentery is attached below and to right of aorta. Jejunal mesenteric vessels form only 1 or 2 arcades, with long and few branches to intestinal wall. While ileum receives many short terminal vessels from a series of 3 or 4or even more arcades. In the jejunal mesentery, fat is deposited near root and is scanty near intestinal wall; while at ileal mesentry, fat is deposited throughout mesentery. Aggregations of lymphoid tissue (Peyer's patches) are present in mucous membrane of lower ileum along anti-mesenteric border. These may be visible through wall of ileum from outside.

Blood Supply Arteries: Superior mesenteric artery. Lowest part of ileum is also supplied by the ileocolic artery. Veins: Superior mesenteric vein. Lymph Drainage: Superior mesenteric nodes. Nerve Supply: sympathetic and parasympathetic (vagus).

Meckel's diverticulum It is remnant of proximal part of the yolk stalk (vitelline duct), which extends into the umbilical cord in embryo and lies on antimesenteric border of ileum. Rule of 2: 2 inches long, occurs in 2% of population and about 2 feet from ileocecal junction. May produce symptoms in a small number of patients (Meckel’s Diverticulutis)

Large Intestine It extends from ileum to anus and is divided into cecum, appendix, ascending colon, transverse colon, descending colon, sigmoid, rectum & anal canal. Function of large intestine is absorption of water and electrolytes and storage of undigested material until expelled from body as feces. Longitudinal muscle of the colon is restricted to three flat band called teniae coli.

Cecum It is a blind-ended pouch situated in right iliac fossa and lies below level of ileocecal junction. It is completely covered with peritoneum and considerably mobile. Peritoneal folds create superior ileocecal, inferior ileocecal, and retrocecal recesses. Attached to its posteromedial surface is appendix. teniae coli of the cecum converge on base of appendix and provide it with a complete longitudinal muscle coat. Ileocecal opening is provided with two folds, or lips, which form ileocecal valve. Relations of the cecum: Anteriorly: Small intestine, greater omentum & anterior abdominal wall in right iliac fossa. Posteriorly: Appendix (commonly), Psoas and iliacus muscles, femoral & lateral cutaneous nerve of thigh. Medially: Appendix arises from the cecum on its medial side.

Blood Supply of cecum Arteries: Anterior & posterior cecal arteries form ileocolic artery (branch of superior mesenteric artery) Veins: Drain into superior mesenteric vein. Lymph drainage: Superior mesenteric nodes. Nerve Supply: Sympathetic and parasympathetic (vagus) nerves form superior mesenteric plexus.

ileocecal Valve It consists of 2 horizontal folds of mucous membrane that project around orifice of ileum. It plays little or no part in prevention of reflux of cecal contents into ileum; while circular muscle of lower end of ileum (ileocecal sphincter) serves as a sphincter to controls flow of contents from ileum into colon.

Appendix It is a narrow, muscular tube containing a large amount of lymphoid tissue. Its length from 8 to 13 cm (sometimes 20 cm). Its base is attached to posteromedial surface of cecum about below ileocecal junction and remainder is free. It has a complete peritoneal covering (attached to mesentery of small intestine by a short mesentery (mesoappendix) that contains appendicular vessels and nerves. Arteries: appendicular artery (branch of posterior cecal artery). Veins: appendicular vein drains into posterior cecal vein. Lymphatics: Superior mesenteric nodes. Nerve Supply: sympathetic & parasympathetic (vagus) nerves from superior mesenteric plexus. (Referred pain to umbilicus) T10 (umbilical region pain)

Appendectomy Operation Appendix lies in right iliac fossa and its base is situated at (McBurney's point) 1/3 of line joining right anterior superior iliac spine to umbilicus. Base of appendix is easily found by identifying the teniae coli of cecum and tracing them to base of appendix, where they converge. Common Positions of Tip of Appendix: Pelvic position: hanging down into pelvis against right pelvic wall. (b) Retrocecal position: coiled up behind cecum. (c) Paracecal position: projecting upward along lateral side of cecum. (d) Pre-ileal or Retro-ileal postion: in front of or behind terminal part of ileum.

Ascending Colon It lies in right lower quadrant and extends upward from cecum to inferior surface of right lobe of liver, where it turns to the left, forming right colic flexure, and becomes continuous with transverse colon. Peritoneum covers front and sides of ascending colon. Relations: Anteriorly: Coils of small intestine, greater omentum & anterior abdominal wall. Posteriorly: Iliacus, iliac crest, quadratus lumborum, origin of transversus abdominis Muscle & lower pole of right kidney. Ilio- hypogastric & ilioinguinal nerves cross behind it. Blood Supply Arteries: ileocolic & right colic branches of superior mesenteric artery. Veins: drain into superior mesenteric vein. Lymph Drainage: Superior mesenteric nodes. Nerve Supply: Sympathetic &parasympathetic (vagus) nerves from superior mesenteric plexus.

Transverse Colon It extends across abdomen, occupying umbilical region. It begins at right colic flexure below right lobe of liver and hangs downward, suspended by transverse mesocolon from pancreas. It then ascends to left colic flexure below the spleen. Left colic flexure is higher than the right one and is suspended from the diaphragm by phrenicocolic ligament. Relations: Anteriorly: Greater omentum & anterior abdominal wall. Posteriorly: 2nd part of duodenum, head of the pancreas& jejunum & ileum. Blood Supply: Arteries: proximal 2/3 by middle colic Artery (superior mesenteric artery). Distal 1/3 by left colic artery (inferior mesenteric artery). Veins: Superior and inferior mesenteric veins. Lymph Drainage: proximal 2/3 into colic nodes (superior mesenteric nodes); distal 1/3 into colic nodes (inferior mesenteric nodes). Nerve Supply: proximal 2/3 by Superior mesenteric plexus; distal 1/3 pelvic splanchnic nerves through inferior mesenteric plexus.

Descending Colon It extends downward from left colic flexure, to pelvic brim, where it becomes continuous with sigmoid colon. Peritoneum covers front &sides Relations: Anteriorly: Coils of small intestine, greater Omentum & anterior abdominal wall. Posteriorly: Lateral border of left kidney, origin of transversus abdominis muscle, quadratus lumborum, iliac crest, iliacus, and left psoas. Iliohypogastric & ilioinguinal nerves, femoral nerve & lateral cutaneous nerve of thigh, lie posteriorly. Blood Supply: Arteries: left colic and sigmoid branches of inferior mesenteric artery. Veins: inferior mesenteric vein. Lymph Drainage: inferior mesenteric nodes. Nerve Supply: Sympathetic & parasympathetic pelvic splanchnic nerves (inferior mesenteric plexus)

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