Colon Flashcards
lymphatic drainage of the colon
The lymphatic drainage of the ascending and transverse colon is into the superior mesenteric nodes. The descending colon and sigmoid drain into the inferior mesenteric nodes.
Most of the lymph from the superior mesenteric and inferior mesenteric nodes passes into the intestinal lymph trunks, and on to the cisterna chyli – where it ultimately empties into the thoracic duct.
innervation fthe colon
he innervation to the colon is dependent on embryological origin:
Midgut-derived structures (ascending colon and proximal 2/3 of the transverse colon) receive their sympathetic, parasympathetic and sensory supply via nerves from the superior mesenteric plexus.
Hindgut-derived structures (distal 1/3 of the transverse colon, descending colon and sigmoid colon) receive their sympathetic, parasympathetic and sensory supply via nerves from the inferior mesenteric plexus:
Parasympathetic innervation via the pelvic splanchnic nerves
Sympathetic innervation via the lumbar splanchnic nerves.
veinous drainge of the colon
The venous drainage of the colon is similar to the arterial supply:
Ascending colon – ileocolic and right colic veins, which empty into the superior mesenteric vein.
Transverse colon – middle colic vein, which empties into the superior mesenteric vein.
Descending colon – left colic vein, which drains into the inferior mesenteric vein.
Sigmoid colon – drained by the sigmoid veins into the inferior mesenteric vein.
The superior mesenteric and inferior mesenteric veins ultimately empty into the hepatic portal vein. This allows toxins absorbed from the colon to be processed by the liver for detoxification.
which part of the colon is midgut and which is hindgut
Ascending colon and proximal 2/3 of the transverse colon – derived from the midgut.
Distal 1/3 of the transverse colon, descending colon and sigmoid colon – derived from the hindgut.
arteiral supply od the colon
As a general rule, midgut-derived structures are supplied by the superior mesenteric artery, and hindgut-derived structures by the inferior mesenteric artery.
The ascending colon receives arterial supply from two branches of the superior mesenteric artery; the ileocolic and right colic arteries. The ileocolic artery gives rise to colic, anterior cecal and posterior cecal branches – all of which supply the ascending colon.
The transverse colon is derived from both the midgut and hindgut, and so it is supplied by branches of the superior mesenteric artery and inferior mesenteric artery:
Right colic artery (from the superior mesenteric artery)
Middle colic artery (from the superior mesenteric artery)
Left colic artery (from the inferior mesenteric artery)
The descending colon is supplied by a single branch of the inferior mesenteric artery; the left colic artery. The sigmoid colon receives arterial supply via the sigmoid arteries (branches of the inferior mesenteric artery).
what is ant and post to the ascending colon?
Small intestine
Greater omentum
Anterior abdominal wall
Iliacus and quadratus lumborum
Right kidney
Iliohypogastric and ilioinguinal nerves
what is ant and post to the transverse colon?
Greater omentum
Anterior abdominal wall
Duodenum
Head of the pancreas
Jejunum and ileum
what is ant and post to the descending colon?
Small intestine
Greater omentum
Anterior abdominal wall
Iliacus and quadratus lumborum
Left kidney
Iliohypogastric and ilioinguinal nerves
what is ant and post to the sigmoid colon?
Urinary bladder
Uterus and upper vagina (females only)
Rectum
Sacrum
Ileum
whar are the paracolic gutters and what do thery do
The paracolic gutters are two spaces between the ascending/descending colon and the posterolateral abdominal wall.
These structures are clinically important, as they allow infective material that has been released from abdominal organs to accumulate elsewhere in the abdomen.
gow to differential small and large bowel
attached to the surface of the large intestine are omental appendices – small pouches of peritoneum, filled with fat.
Running longitudinally along the surface of the large bowel are three strips of muscle, known as the teniae coli. They are called the mesocolic, free and omental coli.
The teniae coli contract to shorten the wall of the bowel, producing sacculations known as haustra.
The large intestine has a much wider diameter compared to the small intestine
where do the differnces between small and large bowel end
These features cease at the rectosigmoid junction, where the smooth muscle of the teniae coli broaden to form a complete layer within the rectum.
dessibe the course of the asending colon
The colon begins as the ascending colon, a retroperitoneal structure which ascends superiorly from the caecum. When it meets the right lobe of the liver, it turns 90 degrees to move horizontally. This turn is known as the right colic flexure (or hepatic flexure), and marks the start of the transverse colon.
dessibe the course of the decending colon
After the left colic flexure, the colon moves inferiorly, and so is termed the descending colon. It is retroperitoneal in the majority of individuals, but is located anteriorly to the left kidney, passing over its lateral border. When the colon begins to turn medially, it becomes the sigmoid colon.
dessibe the course of the transverse colon
The transverse colon crosses the abdomen, extending from the right colic flexure to the spleen, where it turns another 90 degrees to point inferiorly. This turn is known as the left colic flexure (or splenic flexure). Here, the colon is attached to the diaphragm by the phrenicocolic ligament.
The transverse colon is the least fixed part of the colon, and is variable is position – it can dip into the pelvis in tall, thin individuals. Unlike the ascending and descending colons, the transverse colon is intraperitoneal.
