Superior rectal from the inferior mesenteric, middle rectal from the internal iliac, inferior rectal from the internal pudendal
Mnemonic
Three arteries, from three different sources, which is why the rectum survives so well:
- Superior rectal, from the inferior mesenteric artery, the continuation of the hindgut supply
- Middle rectal, from the internal iliac
- Inferior rectal, from the internal pudendal
Venous drainage splits at the pectinate line: the superior rectal vein drains to the portal system via the inferior mesenteric, while the middle and inferior drain to the systemic system via the internal iliac. This makes the anorectum a portosystemic anastomosis.
Lymphatic drainage follows the same line: above to the inferior mesenteric and internal iliac nodes, below to the superficial inguinal nodes, which determines the nodal fields irradiated in rectal and anal cancer.
Expansion
| Artery | Origin | Territory |
|---|---|---|
| Superior rectal | Inferior mesenteric (hindgut) | Upper rectum |
| Middle rectal | Internal iliac | Middle rectum |
| Inferior rectal | Internal pudendal | Lower rectum and anal canal |
Venous drainage mirrors this and creates a portosystemic anastomosis:
- Superior rectal vein → inferior mesenteric vein → portal system
- Middle and inferior rectal veins → internal iliac → systemic system
The rich anastomosis between three sources means rectal ischaemia is rare, and it allows the rectal stump to survive after ligation of the inferior mesenteric artery.
It also means drugs absorbed from the lower rectum partly bypass first-pass hepatic metabolism, which is relevant to rectal drug administration.