Mesentery Proper

The mesentery proper is a fan-shaped double layer of visceral peritoneum that suspends the jejunum and ileum from the posterior abdominal wall. It provides a flexible anchor that permits mobility while carrying vital blood vessels, lymphatics, and nerves between the intestines and the systemic circulation. Despite appearing delicate, the mesentery proper is a structurally complex and clinically important structure, especially in surgeries involving the small bowel, trauma, or ischemic disease.

Structure

The mesentery proper is composed of two closely apposed layers of visceral peritoneum enclosing adipose tissue, vasculature, lymphatics, and autonomic nerves. These peritoneal folds arise from embryonic mesoderm and retain continuity between the jejunoileal loops and the posterior abdominal wall.

Layers and Composition

• Peritoneal layers: Two layers of visceral peritoneum

• Connective tissue core: Fat, loose connective tissue, and mesothelial lining

• Vascular structures: Superior mesenteric artery and vein, jejunal and ileal branches

• Lymphatics: Central lacteals, mesenteric lymph nodes, and collecting vessels

• Nerve supply: Autonomic plexuses (sympathetic from T10–T12, parasympathetic from vagus)

Contained Vessels and Pathways

Structure Function Superior mesenteric artery (SMA) Main arterial supply to jejunum and ileum Superior mesenteric vein Drains blood from small intestine into portal vein Jejunal and ileal branches Form arcades and vasa recta to supply intestinal wall Mesenteric lymph nodes Drain intestinal lymph toward preaortic lymphatics

Location

The mesentery proper is located in the central abdominal cavity. It suspends the jejunum and ileum from the posterior abdominal wall and allows their mobility while maintaining vascular continuity.

Root of the Mesentery

• Length: Approximately 15 cm

• Orientation: Oblique line from the left side of L2 to the right sacroiliac joint

• Structures crossed: Third part of the duodenum, abdominal aorta, inferior vena cava, right ureter, right psoas major muscle

Extent of Coverage

• Proximal attachment: Root of the mesentery on posterior abdominal wall

• Distal spread: Fans out to enclose approximately 6 meters of jejunum and ileum

The peripheral edge of the mesentery is long and convoluted, allowing the small intestine to move within the confines of the abdominal cavity without twisting its vascular supply under normal conditions.

Function

The mesentery proper serves both supportive and physiological functions vital to the health and function of the small intestine.

Mechanical Functions

• Suspension: Holds the jejunum and ileum in place while allowing motility

• Flexibility: Permits peristalsis and intestinal movement without tearing vessels

Conduction of Structures

• Vascular: Provides the main pathway for arteries, veins, and vasa recta

• Lymphatic: Carries lymph from intestinal villi to regional nodes

• Neurological: Transmits autonomic signals for motility and secretion

Immune and Absorptive Support

• Lymph nodes: Monitor intestinal immunity and act as first-line defense

• Fat padding: Cushions vessels and allows for storage and protection

Clinical Significance

Mesenteric Ischemia

Occlusion or narrowing of the superior mesenteric artery or its branches can compromise blood supply to the jejunum and ileum, leading to ischemia. This is a surgical emergency.

• Acute: Sudden severe pain, usually embolic or thrombotic

• Chronic: Postprandial pain, weight loss, fear of eating

Volvulus

Rotation of the bowel around the mesenteric root can lead to obstruction and vascular compromise.

• Can occur due to congenital malrotation

• Most commonly affects sigmoid colon but can involve small intestine

Internal Herniation

Loops of small intestine may herniate through defects in the mesentery or postoperative spaces, leading to intermittent obstruction or ischemia.

Mesenteric Lymphadenopathy

Enlargement of mesenteric lymph nodes is commonly seen in:

• Viral or bacterial gastroenteritis

• Tuberculosis

• Lymphoma or metastatic carcinoma

Surgical Implications

• Bowel resection: Involves dividing and controlling mesenteric vessels

• Risk of devascularization: During segmental resection, understanding arcade patterns is crucial

Embryological Development

The mesentery proper is derived from the embryonic dorsal mesentery, which suspends the entire gut tube in the peritoneal cavity during development. As the midgut elongates and rotates, part of the dorsal mesentery persists to become the adult mesentery proper.

• Week 5–10 of development: Gut herniates and rotates 270° around the SMA

• Jejunum and ileum: Retain a mesentery; other regions (like duodenum and ascending colon) become secondarily retroperitoneal

Comparison Table

Feature Mesentery Proper Transverse Mesocolon Sigmoid Mesocolon Attaches to Jejunum and ileum Transverse colon Sigmoid colon Root location L2 to right iliac fossa Pancreatic neck to anterior wall Pelvic brim to rectosigmoid junction Blood supply Jejunal and ileal branches (SMA) Middle colic artery (SMA) Sigmoid branches (IMA) Clinical notes Volvulus, ischemia, hernia Volvulus, mesocolon tumors Common site for volvulus in elderly