Study guide
Study guide

Gastrointestinal blood supply

Outline the anatomy of the blood supply (arteries and veins) of the gastrointestinal system

Arterial supply

Oesophageal arterial supply

The oesophagus has a segmental arterial supply:

  • Upper third: Inferior thyroid artery
  • Middle third: Oesophageal branches of the thoracic aorta
  • Lower third: Left gastric artery

Coeliac trunk

Branches from the aorta at the T12 level.

Supplies the foregut:

  • distal third of the oesophagus
  • proximal duodenum
  • liver
  • spleen
  • pancreas

Major Branches

  • Left gastric artery
    • Anastomoses with the right gastric artery to supply the lesser curvature of the stomach
  • Splenic artery
    • Supplies the spleen
    • Gives rise to the left gastroepiploic artery
      • Which anastomoses with the right gastroepiploic artery to supply the greater curvature of the stomach
  • Common hepatic artery, which gives rise to several important branches:
    • Gastroduodenal artery, giving rise to:
      • Right gastroepiploic artery
      • Superior pancreaticoduodenal arteries → pancreas and duodenum
    • Right gastric artery → lesser curvature of the stomach
    • Hepatic artery proper, giving rise to:
      • Right and left hepatic arteries → liver
      • Cystic artery → gallbladder

Superior mesenteric artery (SMA)

Branches from the aorta at L1.

Supplies the midgut (distal duodenum → proximal two-thirds of transverse colon).

Major branches

  • Inferior pancreaticoduodenal artery
    • Supplies the pancreas and duodenum
    • Forms anastomoses with superior pancreaticoduodenal arteries
  • Jejunal and ileal arteries
    • supply the jejunum and ileum
    • Arranged in arterial arcades (a series of interconnected arterial arches)
    • Give rise to arteriae rectae (straight branches that connect the arcades to the bowel itself)
  • Ileocolic, right colic, and middle colic arteries
    • Supply the caecum, ascending colon and transverse colon respectively, up to the splenic flexure
    • Do not have arcades
    • Instead they have longer arteriae rectae

Inferior mesenteric artery (IMA)

Branches from the aorta at L3.

Supplies the hindgut (distal transverse colon → upper rectum).

Major Branches

  • Left colic artery &rar; descending colon
  • Sigmoid arteries → sigmoid colon
  • Superior rectal artery → upper third of the rectum, down to the dentate line

These branches don't have arcades either. They supply the distal colon via long arteriae rectae.

Watershed ischaemia

The splenic flexure and rectosigmoid junction are both regions 'in betweeen' two major arterial supplies. The splenic flexure lies between the SMA and IMA supply, while the rectosigmoid junction lies between the last sigmoid arterial branch and the superior rectal artery supply.

This property makes them more prone to ischaemia during periods of low blood flow or pressure. The splenic flexure in particular is the most common site of ischaemic colitis.

Rectal blood supply

Above the dentate line:

  • Superior rectal artery → upper third of the rectum, down to the dentate line

Below the dentate line:

  • Supplies the remaining two thirds of the rectum from systemic arterial supply
  • Middle rectal artery: branch of the internal iliac artery
  • Inferior rectal artery: branch of the inferior pudendal artery
Dentate line

The dentate (pectinate) line is an anatomical landmark in the anal canal that marks the junction between endodermal and ectodermal epithelium.

Above the dentate line:

  • Epithelium is columnar (like many mucosal surfaces)
  • Can be considered a 'visceral organ' with visceral innervation, blood supplied/drained from the IMA and portal vein, and lymphatic drainage via deep internal iliac nodes

Below the dentate line:

  • Epithelium is stratified squamous (like skin)
  • Can be considered an 'external' or 'peripheral' organ with somatic innervation, blood supplied/drained by systemic arteries/veins, and lymphatic drainage to the comparatively superficial inguinal nodes
The dentate line and pain

Somatic innervation of the rectum below the dentate line allows for strong pain signals that are well localised. By contrast, visceral innervation above the dentate line causes poorly localised pain.

This feature has major clinical relevance to the localisation of pathology. For example painless rectal bleeding may indicate pathology above the dentate line (e.g. internal haemorrhoids, rectal cancer), while painful bleeding may indicate pathology below the dentate line (e.g. external haemorrhoids, anal fissure, anorectal extension of cancer).

Venous drainage

Oesophagus

  • Upper third → Inferior thyroid veins → systemic circulation
  • Middle third → Azygos and hemiazygos veins → systemic circulation
  • Lower third → Left gastric vein → portal vein
Clinical relevance

The transition between systemic and portal venous drainage explains the portosystemic anastomoses at the distal oesophagus and proximal stomach. Portosystemic anastomoses also occur in the rectum. This is why oesophageal/gastric/rectal varices form in portal hypertension.

Abdominal GI Tract

  • Foregut (organs supplied by the coeliac trunk)
    • Drain via corresponding veins → portal vein
    • e.g. the regions supplied the the right and left gastric arteries are drained by the right and left gastric veins
  • Midgut (organs supplied by the SMA)
    • Drain via corresponding veins → superior mesenteric vein (SMV) → portal vein
  • Hindgut (organs supplied by the IMA)
    • Drain via corresponding veins → inferior mesenteric vein (IMV) → portal vein

Portal circulation

  • Portal vein → liver → hepatic veins → inferior vena cava

Rectum

Above dentate line: superior rectal vein → IMV → portal vein

Below dentate line: middle and inferior rectal veins → systemic circulation

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