Superior Mesenteric Artery

Original Editor - Kardelen Aktas Top Contributors - Stacy Lawrence, Vidya Acharya, Kardelen Aktas and Alexandra Stead

Introduction

The superior mesenteric artery (SMA) is a major anterior branch of the abdominal aorta that provides arterial blood supply to the midgut structures. It plays a critical role in maintaining the blood supply to a significant portion of the gastrointestinal tract, including parts of small intestine and the large intestine. Understanding the anatomy and physiology of the superior mesenteric artery is essential for clinicians, particularly when considering vascular disorders, abdominal surgeries, and diagnostic imaging interpretation.

Anatomy

Origin

The superior mesenteric artery arises from the anterior surface of the abdominal aorta at the level of the first lumbar vertebra (L1), approximately 1 centimetre inferior to the origin of the coeliac trunk and superior to the renal arteries. This corresponds anatomically to the transpyloric plane.

Course

After its origin, the superior mesenteric artery follows a characteristic path through he abdomen:

1. Initial descent: The artery courses anteriorly and inferiorly from the aorta
2. Posterior to pancreas: It passes behind the neck of the pancreas and the splenic vein
3. Entry into mesentery: The SMA emerges from behind the lower border of the pancreatic neck and enters the mesentery of the small intestine
4. Terminal course: It continues infero-laterally towards the right iliac fossa terminating by anastomosing with branches of the ileocolic artery

Anatomical Relations

Anterior relations:

• Pylorus of the stomach
• Neck of the pancreas
• Splenic vein

Posterior relations:

• Left renal vein (which courses between the aorta and the SMA)
• Uncinate process of the pancreas
• Third (horizontal) portion of the duodenum

Lateral relations:

• The superior mesenteric vein typically runs to the right side of the artery

Branches of the Superior Mesenteric Artery

The superior mesenteric artery gives rise to several major branches that supply blood to the pancreas, small intestine, and portions of the large intestine. These branches arise in characteristic pattern:

Inferior Pancreaticoduodenal Artery

Origin: First branch of the SMA, arising from its right side shortly after SMA emerges from behind pancreas .

Course and distribution:

• Divides into anterior and posterior branches
• Both branches pass between the C-shape curve and the duodenum and the head of the pancreas
• Forms anastomoses with the superior pancreaticoduodenal artery (a branch of the gastroduodenal artery from the coeliac trunk)

Supply:

• Head of the pancreas
• Second, third, and fourth parts of the duodenum (distal to the major duodenal papilla)

Jejunal and Ileal Arteries

Origin: Multiple branches (approximately 4-6 jejunal and 8-13 ileal arteries) arising from the left side of the SMA. These arteries have a unique characteristics where the arteries

Jejunal Blood Supply:

• Fewer arterial arcades (1-2 rows)
• Longer vasa recta
• Larger diameter vessels

Ileal Blood Supply :

• More arterial arcaded (3-4 rows)
• Shorter vasa recta
• Smaller diameter vessels

Clinical significance: This difference in vascular patterns reflects the functional differences between the jejunum (site of maximum nutrient absorption) and ileum.

Supply:

• Jejunum (middle portion of small intestine)
• Ileum (terminal portion of small intestine)

Middle Colic Artery

Origin: Arise from the right side of the SMA, just below the pancreas.

Course:

• Travels superiorly within the transverse mesocolon
• Divides into right and left branches

Anastomoses:

• Right branch: anastomoses with the right colic artery
• Left branch: anastomoses with the left colic artery (from the inferior mesenteric artery)

Supply:

• Proximal two-thirds of the transverse colon

Right Colic Artery

Origin: Arises from the right side of the SMA, inferior to the middle colic artery. The right colic artery demonstrates significant anatomical variation and may be absent in up 10-20% of individuals.

Course:

• Passes to the right towards the ascending colon
• Typically divides into ascending and descending branches

Supply:

• Ascending colon

Ileocolic Artery

Origin: The most inferior major branch of the SMA, arising from its right side.

Course:

• Passes inferiorly and to the right
• Divides into multiple branches

Branches includes:

• Ascending branch: Supplies the ascending colon
• Anterior and posterior caecal arteries: Supply the caecum
• Appendicular artery: Supplies the appendix
• Ileal branch: Supplies the terminal ileum

Supply:

• Terminal ileum
• Caecum
• Appendix
• Proximal ascending colon

Clinical relevance: During appendectomy, the appendicular artery must be ligated to prevent bleeding.

Anastomoses and Collateral Circulation

The superior mesenteric artery forms crucial anastomoses with other mesenteric vessels, providing collateral circulation that can maintain intestinal blood supply if one vessel becomes occluded.

Physiological Function

Blood Supply to the Midgut

The primary function of the superior mesenteric artery is to deliver oxygenated blood and nutrients to the organs derived from the embryonic midgut.

Key supplied structures are:

• Pancreatic head (shared with coeliac trunk)
• Duodenum (third and fourth parts)
• Jejunum
• Ileum
• Caecum and appendix
• Ascending colon
• Proximal two-thirds of transverse colon