Rectum and upper anal canal
Organ supplied · Hindgut
Termination of the hindgut, supplied chiefly by the superior rectal artery down to the pectinate line and reinforced by the middle rectal (internal iliac) and inferior rectal (internal pudendal) arteries. This triple supply makes rectal infarction rare, and the pectinate line marks the portosystemic and visceral–somatic boundary.
Traced from the start
- Abdominal aorta
- Inferior mesenteric artery
- Superior rectal artery
- Rectum and upper anal canal
Detail
- Above pectinate line
- Superior rectal (IMA) + middle rectal (internal iliac); visceral sensation, painless
- Below pectinate line
- Inferior rectal (internal pudendal); somatic sensation via pudendal nerve, painful
- Venous
- Superior rectal → portal; middle and inferior rectal → systemic — a portosystemic anastomosis
When it goes wrong
Engorgement of the anal cushions above the pectinate line
Internal haemorrhoids at 3, 7 and 11 o'clock: painless bright-red bleeding on the paper; external haemorrhoids below the line are exquisitely painful (pudendal innervation)
IMA occlusion or ischaemic colitis
Rectum is spared by internal iliac collaterals — rectal sparing on endoscopy points to ischaemic rather than ulcerative colitis
Practise this structure
1 question in the bank tagged Hindgut.