Overview

The terminal ileum pushes into the posteromedial wall of the caecum, forming upper and lower lips that meet at the sides as frenula. The circular muscle here is thickened into the ileocaecal sphincter, which normally maintains a modest tone.

After a meal the gastroileal reflex, together with gastrin, relaxes the sphincter and increases ileal peristalsis, so chyme moves on into the colon. Distension or irritation of the caecum contracts the sphincter and inhibits ileal peristalsis. This keeps the colon's dense bacterial population out of the small bowel. Ileal chyme passes the valve at roughly 1.5 L a day.

Location: Right iliac fossa, on the posteromedial wall of the caecum, about 2 cm above the opening of the appendix.

Anatomy

Innervation: Myenteric plexus with vagal and sympathetic input via the superior mesenteric plexus. Sympathetic activity contracts the sphincter.
Arterial supply: Ileocolic artery (from the SMA).

Function

Regulates passage of ileal chyme into the colon.
Prevents colonic reflux into the ileum and so protects against small-intestinal bacterial overgrowth.

Clinical significance

Closed-loop large bowel obstruction

If a distal colonic obstruction occurs while the ileocaecal valve is competent, gas and fluid cannot decompress back into the small bowel. The caecum, the widest part with the highest wall tension (Laplace's law), distends progressively and can perforate once its diameter exceeds about 10–12 cm.

Loss of the valve

Resection of the ileocaecal region speeds transit and allows colonic bacteria to colonise the small bowel (SIBO). It adds to diarrhoea and malabsorption in short bowel syndrome.

Test yourself

Regarding Meckel diverticulum, which statement is correct?

It is a remnant of the urachus
It lies on the mesenteric border of the jejunum
It occurs in about 20% of the population
It is a true diverticulum about 60 cm (2 ft) proximal to the ileocaecal valve and may contain gastric mucosa

Answer: It is a true diverticulum about 60 cm (2 ft) proximal to the ileocaecal valve and may contain gastric mucosa

It is a persistent vitelline duct, a true diverticulum on the antimesenteric border of the ileum. Rule of 2s: about 2% of people, about 2 ft from the ileocaecal valve, about 2 inches long, 2 ectopic tissues (gastric, pancreatic), and usually presents before age 2. Ectopic gastric acid causes painless bleeding.