Colon• Extends superiorly from the cecum.• Consists of 4 parts: -ascending colon -transverse colon -descending colon -sigmoid colon• Ascending anddescending segments are retroperitoneal andtransverse and sigmoidsegments are intraperitoneal.
Ascending Colon• Lies in the right lower quadrant of trunk.• It extends from the cecum, upward to the inferior surface of right lobe of liver.• At this position, it turns left to form the right colic flexure and becomes continuous with the transverse colon.• The peritoneum covers the front and the sides of the ascending colon and binds it to the posterior abdominal wall.
Relations of ascending colon:Anterior relations:• Coils of small intestine• Greater omentum• Anterior abdominal wallPosterior relations:• Iliacus muscle• Iliac crest• Quadratus lumborum muscle• Origin of transversus abdominis muscle• Lower aspect of the right kidney• Iliohypogastric and ilioinguinal nerves
• Blood supply:Arteries-ileocolic and-right colic branches of the superior mesenteric arteryVeins-The veins correspond to the arteries and eventually drain intothe superior mesenteric vein.• Lymph drainage:-The lymph vessels drain into lymph nodes lying along the courseof the blood vessels of the ascending colon. Ultimately thelymph reaches the superior mesenteric lymph nodes.• Nerve supply to ascending colon:- receives sympathetic and parasympathetic nerves from thesuperior mesenteric plexus.
Transverse Colon• Passes from righthypochondriac region intoleft hypochondriac region.• Extends from right colicflexure to left colic flexurebelow the spleen.• The left colic flexure ishigher and more posterior than the right colic flexure,and is attached to thediaphragm by the phrenicocolicligament.• The transverse colon has its ownmesentery, known as the transversemesocolon. It suspends the transverse colon from the anterior borderof pancreas.
Relations of transverse colon:• Anterior relations:-Greater omentum-Umbilical and hypogastric regions of anteriorabdominal wall• Posterior relations:-Descending part of theduodenum-Head of the pancreas-Coils of jejunum and ileum• superior relations – – Liver – Gall-bladder – Greater curvature of stomach – Lower end of spleen• Inferior relations– – Small intestine
• Blood supply:Arteries-proximal 2/3 by medial colic artery(branch of superior mesentericartery)-distal 1/3 by left colic artery(branch of inferior mesenteric artery)Veins-The veins correspond to the arteries. Those from the proximal 2/3drain into the superior mesenteric vein and those from the distal 1/3drain into the inferior mesenteric vein.• Lymph drainage:-The lymph from the proximal 2/3 drain into the superior mesentericnodes, via the colic nodes.-the lymph from the distal 1/3 drains into the inferior mesentericnodes, via the colic nodes.• Nerve supply to ascending colon:-The proximal 2/3 are innervated by sympathetic and parasympatheticnerves from the superior mesenteric plexus.-The distal 1/3 innervated by sympathetic and parasympathetic fibersfrom the inferior mesenteric plexus.
Descending Colon• lies at the left side of theabdomen in both the upperand lower quadrants.• Begins at the left colicflexure and ends bybecoming continuous with the sigmoid colon, at thepelvic brim.• is covered from the frontand sides by the peritoneum,which binds it to the posteriorabdominal wall.
Relations of descending colon:• Anterior relations:-Coils of small intestine-Greater omentum-Anterior abdominal wall• Posterior relations:-Lateral border of leftkidney-Origin of transversus abdominis muscle-Quadratus lumborum muscle-Iliac crest-Iliacus muscle-Left psoas muscle-Iliohypogastric and Ilioginuinal nerves-Lateral cutaneous nerve of thigh-Femoral nerve
• Blood supply:Arteries-left colic artery and-sigmoid artery (branches of inferior mesenteric artery)Veins-The veins correspond to the arteries and eventually draininto the inferior mesenteric vein.• Lymph drainage:-The lymph first drains into the colic lymph nodes, fromwhere it eventually drains to the inferior mesentericlymph nodes, which are situated around the root ofinferior mesenteric artery.• Nerve supply to ascending colon:- receives sympathetic and parasympathetic pelvicsplanchnic nerves through the inferior mesenteric plexus.
Sigmoid Colon• Begins where descendingcolon passes in front of the pelvic brim. Below, itbecomes continuous with the rectum at the level of S3.• Completely surrounded by peritoneum.• Sigmoid colon is mobileup to a certain extent.• It hangs down into the pelviccavity in the form of a loop. It isattached to the posterior wall ofthe pelvis by a fan shaped fold of peritoneum, known as sigmoid mesocolon. 1-lesser omentum 2-transverse mesocolon 3-small bowel mesentery 4-sigmoid mesentery
Relations of sigmoid colon:• Anterior relations:-Urinary bladder (in males)-Posterior surface of uterus andupper part of vagina (in females)• Posterior relations:-Lower coils of terminalpart of ileum-Rectum-Sacrum-external iliac vessels-left piriformis-left sacral plexus of nerves
• Blood supply:Arteries -sigmoid branches of the inferior mesenteric artery.Veins-venous drainage through the inferior mesentericvein, which eventually drains into the portal venoussystem.• Lymph drainage:-The nodes that receive lymph fromsigmoid colon lie along the course of the sigmoidarteries. From these nodes, the lymph eventuallydrains into the inferior mesenteric lymph nodes.• Nerve supply to ascending colon:-Inferior hypogastric plexus supplies both thesympathetic and parasympathetic nerves.