QS Study

Anal Canal: Blood Supply, Nerve Supply, and Development

Anal Canal is the terminal part of the large intestine, situated below the levels of the pelvic diaphragm. It is the last spot where stools pass through before finally exiting the body. Muscles that surround the anal canal relax to allow waste to leave your body. It serves to lubricate and transmit fecal matter as it passes from the rectum to outside the body.

Blood Supply:

  • Blood supply of upper half of anal canal:

Arterial supply is through the superior rectal artery, which is a branch of the inferior mesenteric artery. Venous drainage is by way superior rectal vein, which is a tributary of the inferior mesenteric vein.

  • Blood supply of the lower half of anal canal:

Arterial supply is through the inferior rectal artery, which is a branch of the internal pudendal artery. Venous drainage is by way of an inferior rectal vein, a tributary of the internal pudendal vein.

Fig: Blood supply of anal canal

Nerve Supply

(a) Above the pectinate line:

  • Sympathetic – From inferior hypogastric plexus (L 1, 2).
  • Parasympathetic – From pelvic splanchnic nerve (S 2, 3, 4).
  • Visceral innervation via the inferior hypogastric plexus.
  • Sensitive to stretch.

(b) Below the pectinate line: Somatic nerves (Inferior rectal, S 2, 3, 4).

  • Somatic innervation via the inferior anal nerves (branches of the pudendal nerve)
  • Sensitive to pain, temperature, touch, and pressure.

Development

(1) Above the pectinate line – From endodermal cloaca.

(2) Below the pectinate line – From ectodermal proctodeum.