Arterial supply of the gut
Gut Arteries: Coeliac Trunk, SMA, IMA, Anastomoses and Watershed Areas
Arterial supply of the gut for FCPS Part 1: coeliac trunk, superior and inferior mesenteric arteries, their levels, branches, relations and anastomoses. Covers ulcer bleeding, mesenteric ischaemia, watershed areas, coeliac plexus and malrotation.
Three trunks for three gut regions
| Artery | Level | Territory | Pain referred to |
|---|---|---|---|
| Coeliac trunk | T12 | Foregut: lower oesophagus to D2 (major papilla), liver, gallbladder, upper pancreas; also spleen | Epigastrium |
| Superior mesenteric (SMA) | L1 | Midgut: D2 below papilla to proximal two-thirds of transverse colon | Periumbilical |
| Inferior mesenteric (IMA) | L3 | Hindgut: distal third of transverse colon to upper anal canal | Suprapubic |
- Visceral pain follows the artery and its sympathetic supply, which is why gut pain is referred by embryological region.
- The middle third of the oesophagus is supplied by oesophageal branches of the descending thoracic aorta; the lower third by the left gastric.
Coeliac trunk
- A short trunk arising just below the median arcuate ligament of the diaphragm; it divides into three.
- Left gastric: smallest branch; lesser curvature and lower oesophagus. A lesser curvature ulcer bleeds from it.
- Common hepatic: gives the gastroduodenal artery (behind the first part of the duodenum), then continues as hepatic artery proper (right gastric, right and left hepatic; cystic artery usually from the right hepatic). The GDA gives the right gastroepiploic and superior pancreaticoduodenal arteries; a posterior duodenal ulcer erodes it.
- Splenic: largest, tortuous, along the upper border of the pancreas; short gastrics, left gastroepiploic, pancreatic branches including arteria pancreatica magna. A posterior gastric ulcer may erode it.
Superior mesenteric artery
- Arises behind the neck of the pancreas; the body of the pancreas and splenic vein lie between the coeliac trunk and SMA origins.
- Passes in front of the left renal vein (compressed between SMA and aorta in nutcracker syndrome), the uncinate process and the third part of the duodenum (SMA syndrome).
- Branches: inferior pancreaticoduodenal, 15 or more jejunal and ileal branches (from its left side), middle colic, right colic, ileocolic (appendicular branch).
- Acute mesenteric ischaemia: an embolus (atrial fibrillation) lodges just beyond the middle colic origin, sparing proximal jejunum; thrombosis on atheroma blocks the origin. Pain out of proportion to signs, raised lactate, then purple dead bowel.
Inferior mesenteric artery
- Branches: left colic, sigmoid arteries, and its continuation the superior rectal artery (main supply of the rectum).
- Often ligated in aortic aneurysm repair or left-sided colectomy; the colon survives through the marginal artery if it is intact.
Anastomoses between territories
| Anastomosis | Links | Clinical importance |
|---|---|---|
| Pancreaticoduodenal arcades | Coeliac (via GDA) and SMA | Collateral to the liver if coeliac trunk is narrowed |
| Marginal artery (Drummond) | SMA and IMA along the colon | Allows IMA ligation |
| Arc of Riolan | Middle colic and left colic, closer to the mesenteric root | Enlarges in chronic occlusion |
| Rectal anastomoses | Superior rectal (IMA) with middle and inferior rectal (internal iliac) | Pelvic collateral |
- Coeliac stenosis and the Whipple operation: with a tight coeliac trunk, liver flow comes retrogradely from the SMA through the pancreaticoduodenal arcades and the GDA into the common hepatic artery. Test-clamping the GDA abolishes the hepatic pulse; dividing it would cause liver ischaemia.
Watershed areas and ischaemic colitis
- Splenic flexure (Griffiths' point): between middle colic (SMA) and left colic (IMA); marginal artery may be weak.
- Rectosigmoid (Sudeck's point): between the last sigmoid branch and superior rectal artery.
- Ischaemic colitis typically involves the splenic flexure: elderly patient or after aortic surgery, left-sided pain and bloody diarrhoea.
Chronic ischaemia and coeliac compression
- Chronic mesenteric ischaemia ("abdominal angina"): postprandial pain, fear of eating, weight loss; usually two of three trunks are narrowed, with the SMA most important.
- Median arcuate ligament syndrome: a thin young woman with postprandial epigastric pain, weight loss and an epigastric bruit. The ligament compresses the coeliac trunk mainly in expiration; flow velocities fall on deep inspiration as the trunk moves down. A fixed atherosclerotic stenosis does not vary with breathing.
Coeliac plexus and splanchnic nerves
- The greater splanchnic nerve (T5–T9) pierces the crus and synapses mainly in the coeliac ganglion; lesser (T10–T11) in the aorticorenal ganglion; least (T12) in the renal plexus.
- The coeliac plexus surrounds the coeliac trunk and SMA origins. Pain from pancreatic cancer (epigastric, boring through to the back) is visceral and is relieved by a coeliac plexus block, not intercostal blocks.
Midgut rotation
- The midgut loop rotates 270° anticlockwise around the SMA axis, placing the DJ flexure left of the midline and the caecum in the right iliac fossa.
- Malrotation: DJ flexure lies to the right of the spine and the mesentery has a narrow base; Ladd bands may cross the duodenum. The danger is midgut volvulus: bilious vomiting in a newborn, "corkscrew" duodenum on contrast study; SMA flow is cut off, risking loss of the whole midgut.
Bleeding vessels
| Lesion | Vessel |
|---|---|
| Posterior duodenal ulcer | Gastroduodenal |
| Lesser curvature gastric ulcer | Left gastric |
| Posterior gastric wall ulcer | Splenic |
| Diverticular bleeding | Vasa recta (right colon more than left) |
Remember Coeliac T12, SMA L1, IMA L3; foregut, midgut, hindgut; epigastric, umbilical, suprapubic.
Exam trap The SMA supplies colon only up to the proximal two-thirds of the transverse colon.
Exam trap Median arcuate ligament compression worsens on expiration and eases on inspiration.
How FCPS asks about this
- Branch of the coeliac trunk: left gastric, common hepatic, splenic; gastroduodenal comes from the common hepatic.
- Structure between the coeliac trunk and SMA: pancreas (neck/body) with the splenic vein.
- Synapse of the greater splanchnic nerve: coeliac ganglion; coeliac plexus block for pancreatic cancer pain.
- Watershed area of the colon: splenic flexure (Griffiths' point).
- Liver pulse lost when GDA is clamped: coeliac stenosis with retrograde flow from the SMA.
- Bilious vomiting with DJ flexure on the right: malrotation with midgut volvulus.
- Young woman, postprandial pain, bruit varying with breathing: median arcuate ligament syndrome.
Test yourself on this topic
5 of the 37 questions in our bank on this topic. Choose an answer to see why every option is right or wrong.
On the second day after open repair of an infrarenal aortic aneurysm, a 70-year-old man passes bloody diarrhoea and has left-sided abdominal tenderness. His lactate is raised. Sigmoidoscopy shows dusky, oedematous mucosa. Which of the following best explains this?
Answer: Ligation of the inferior mesenteric artery
The inferior mesenteric artery arises from the front of the infrarenal aorta at L3 and is often ligated or covered during aneurysm repair. The sigmoid colon then relies on collaterals from the SMA (via the marginal artery and middle colic) and from the internal iliac arteries (via the rectal arteries). If these are poor, especially when an internal iliac is also excluded, the left colon becomes ischaemic, giving bloody diarrhoea within days. Colonoscopy or sigmoidoscopy confirms it.
Colon ischaemia after AAA
- IMA from aorta at L3
- Often ligated in AAA repair
- Sigmoid depends on marginal artery and internal iliacs
- Bloody diarrhoea day 1–3
Remember Bloody stool after AAA repair: think IMA.
Exam trap Bleeding per rectum after AAA repair is colonic ischaemia until proved otherwise.
Why the other options are wrong
- Clamping above the renal arteries Would threaten the kidneys rather than the colon.
- Injury to the superior mesenteric vein Would cause small bowel venous congestion.
- Damage to the pelvic splanchnic nerves Cause erectile and bladder problems, not ischaemia.
- Embolism to the coeliac trunk Supplies the foregut, not the sigmoid.
In colorectal surgery, which of the following sites is the classical watershed between the lowest sigmoid artery and the superior rectal artery, where perfusion may be poor if the communicating branch is divided?
Answer: Rectosigmoid junction (Sudeck point)
Sudeck critical point lies at the rectosigmoid junction, between the last sigmoid branch and the superior rectal artery. If the superior rectal artery is tied below the last sigmoid branch, the communication may be lost and the rectosigmoid can become ischaemic. Griffith point is the other colonic watershed, at the splenic flexure where the SMA and IMA territories meet through a weak marginal artery. Knowing both helps surgeons choose levels of ligation and anastomosis.
Colonic watershed points
- Griffith: splenic flexure (SMA–IMA)
- Sudeck: rectosigmoid (sigmoid–superior rectal)
- Ischaemia risk in low flow or ligation
- Plan ligation levels around them
Remember Griffith at the bend, Sudeck at the bottom.
Exam trap Do not confuse the two watersheds; the splenic flexure is the commoner site of ischaemic colitis.
Why the other options are wrong
- Splenic flexure (Griffith point) The SMA–IMA watershed, a different site.
- Hepatic flexure Well supplied by right and middle colic.
- Ileocaecal junction Well supplied by the ileocolic artery.
- Anorectal junction Well supplied by middle and inferior rectal arteries.
A 28-year-old thin woman has postprandial epigastric pain and weight loss. An epigastric bruit is louder on expiration. Duplex shows high coeliac trunk velocities that fall on deep inspiration. What is compressing the vessel?
Answer: Median arcuate ligament
The median arcuate ligament joins the right and left crura of the diaphragm in front of the aorta at about T12, just above the origin of the coeliac trunk. If the ligament is low or the trunk arises high, the ligament compresses the trunk. Compression is greatest in expiration, when the diaphragm rises, and eases in inspiration, which explains the varying bruit and duplex findings. Treatment is division of the ligament.
Median arcuate ligament
- Joins the two crura at T12
- Over the coeliac trunk origin
- Compression worse in expiration
- Bruit and postprandial pain
Remember Breathe out, the ligament squeezes.
Exam trap The compression lessens on inspiration, unlike fixed atherosclerotic stenosis.
Why the other options are wrong
- Splenic vein Lies behind the pancreas; does not compress arteries.
- Neck of the pancreas Lies in front of the SMV-portal confluence, below the coeliac trunk.
- Left renal vein Is itself compressed between aorta and SMA (nutcracker).
- Superior mesenteric artery Arises below the coeliac trunk; does not compress it.
After shock, colonoscopy shows ischaemia from the hepatic flexure to the mid-transverse colon. Which of the following arteries supplies this segment?
Answer: Middle colic artery
The middle colic artery arises from the superior mesenteric artery as it enters the small bowel mesentery, runs in the transverse mesocolon and supplies the proximal two-thirds of the transverse colon from the hepatic flexure. The right colic supplies the ascending colon, the ileocolic the caecum and terminal ileum, and the left colic (from the IMA) the distal transverse and descending colon. Its branches join the marginal artery, which may be poor at the splenic flexure.
Colic arteries
- Ileocolic: caecum, terminal ileum
- Right colic: ascending colon
- Middle colic: proximal two-thirds of transverse
- Left colic (IMA): distal third, descending
Remember Middle colic, middle of the colon.
Exam trap The left colic artery comes from the IMA, not the SMA.
Why the other options are wrong
- Right colic artery Supplies the ascending colon.
- Left colic artery From the IMA; supplies the distal transverse and descending colon.
- Ileocolic artery Supplies the caecum, appendix and terminal ileum.
- Sigmoid arteries Supply the sigmoid colon.
A 60-year-old woman has a carcinoma of the caecum. For an oncological right hemicolectomy, the main lymph node basin removed lies along which artery?
Answer: Ileocolic artery
Lymph from the colon follows its arteries: epicolic, paracolic, intermediate (along named vessels) and then central nodes at the root of the vessel. The caecum and ascending colon are supplied by the ileocolic and right colic branches of the SMA, so a caecal cancer spreads to nodes along the ileocolic artery to the SMA root. A right hemicolectomy divides the ileocolic (and right colic) vessels at their origin; the middle colic is divided only for hepatic flexure or proximal transverse tumours.
Colonic lymph drainage
- Lymph follows the arteries
- Caecum: ileocolic nodes
- Divide vessel at its origin
- Middle colic for hepatic flexure lesions
Remember Take the artery, take the nodes.
Exam trap Lymph follows the artery, so the level of vessel ligation sets the node harvest.
Why the other options are wrong
- Inferior mesenteric artery Drains the left colon and rectum.
- Middle colic artery Taken for hepatic flexure and transverse tumours.
- Left colic artery Drains the descending colon.
- Superior rectal artery Drains the rectum.
Where this sits in the CPSP syllabus
- Paper 1: Abdomen, Gut arteries: coeliac, SMA, IMA; watershed areas
- Surgery & Allied, Paper 2: Abdomen, Gut arteries: coeliac, SMA, IMA; watershed areas