Appendix

Function

The appendix is a 6–10 cm lymphoid diverticulum hanging from the caecum, its base fixed where the taeniae coli converge — McBurney's point marks its surface projection one-third from the ASIS to the umbilicus.

Long dismissed as vestigial, it is now appreciated as a lymphoid organ and a 'safe house' — a reservoir of commensal bacteria that repopulates the colon after severe diarrhoea. Its varied positions (retrocaecal 65%, pelvic 30%) explain appendicitis' many disguises.

Blood supply

Appendicular artery — an end artery whose thrombosis explains gangrenous appendicitis.

Nerve supply

Vagus and sympathetic T10 — early umbilical pain before localisation.

Clinical relevance

Appendicitis

Lumen obstruction by a faecolith or lymphoid swelling breeds bacterial overgrowth — anorexia, migration of pain, then peritonism.

Carcinoid tumour

The appendix is one of the commonest sites of neuroendocrine (carcinoid) tumours — usually incidental, occasionally obstructive.

Related conditions

• Appendicitis