Colon

Colon

• Extends superiorly from the cecum.• Consists of 4 parts:

-ascending colon -transverse colon -descending colon -sigmoid colon• Ascending and descending segments are retroperitoneal and transverse and sigmoid segments 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 wall

Posterior 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 into the superior mesenteric vein.

• Lymph drainage:-The lymph vessels drain into lymph nodes lying along the course of the blood vessels of the ascending colon. Ultimately the lymph reaches the superior mesenteric lymph nodes.

• Nerve supply to ascending colon:- receives sympathetic and parasympathetic nerves from the superior mesenteric plexus.

Transverse Colon• Passes from right hypochondriac region into left hypochondriac region.• Extends from right colic flexure to left colic flexure below the spleen.• The left colic flexure is higher and more posterior than the right colic flexure ,and is attached to the diaphragm by the phrenicocolic ligament.• The transverse colon has its own mesentery, known as the transverse mesocolon. It suspends the transverse colon from the anterior border of pancreas.

Relations of transverse colon:• Anterior relations:

-Greater omentum-Umbilical and hypogastric regions of anterior abdominal wall

• Posterior relations:-Descending part of the duodenum-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 mesenteric artery)-distal 1/3 by left colic artery(branch of inferior mesenteric artery)Veins-The veins correspond to the arteries. Those from the proximal 2/3 drain into the superior mesenteric vein and those from the distal 1/3 drain into the inferior mesenteric vein.• Lymph drainage:-The lymph from the proximal 2/3 drain into the superior mesenteric nodes, via the colic nodes. -the lymph from the distal 1/3 drains into the inferior mesenteric nodes, via the colic nodes.• Nerve supply to ascending colon:-The proximal 2/3 are innervated by sympathetic and parasympathetic nerves from the superior mesenteric plexus. -The distal 1/3 innervated by sympathetic and parasympathetic fibers from the inferior mesenteric plexus.

Descending Colon• lies at the left side of the abdomen in both the upper and lower quadrants. • Begins at the left colic flexure and ends by becoming continuous with the sigmoid colon, at the pelvic brim. • is covered from the front and sides by the peritoneum, which binds it to the posterior abdominal wall.

Relations of descending colon:• Anterior relations:-Coils of small intestine-Greater omentum-Anterior abdominal wall• Posterior relations:

-Lateral border of left kidney-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 drain into the inferior mesenteric vein.

• Lymph drainage:-The lymph first drains into the colic lymph nodes, from where it eventually drains to the inferior mesenteric lymph nodes, which are situated around the root of inferior mesenteric artery.• Nerve supply to ascending colon:- receives sympathetic and parasympathetic pelvic splanchnic nerves through the inferior mesenteric plexus.

Sigmoid Colon• Begins where descending colon passes in front of the pelvic brim. Below, it becomes continuous with the rectum at the level of S3.• Completely surrounded by peritoneum.• Sigmoid colon is mobile up to a certain extent.• It hangs down into the pelvic cavity in the form of a loop. It is attached to the posterior wall of the 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 and upper part of vagina (in females)

• Posterior relations:-Lower coils of terminal part 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 mesenteric vein, which eventually drains into the portal venous system.• Lymph drainage:-The nodes that receive lymph from sigmoid colon lie along the course of the sigmoid arteries. From these nodes, the lymph eventually drains into the inferior mesenteric lymph nodes.• Nerve supply to ascending colon:-Inferior hypogastric plexus supplies both the sympathetic and parasympathetic nerves.