Mesentery

Overview

The mesentery is a continuous fold of double-layered peritoneum that attaches portions of the intestine to the posterior abdominal wall. It acts as a supportive and suspensory structure while serving as a conduit for blood vessels, lymphatics, and nerves. Once considered a fragmented structure, recent anatomical understanding classifies the mesentery as a single, continuous organ that plays vital roles in digestion, immunity, and structural integrity of the gut.

Location

The mesentery is located in the abdominal cavity and is classified based on the portion of the gastrointestinal tract it supports:

• The mesentery proper: Connects the jejunum and ileum to the posterior abdominal wall

• Mesocolon: Includes the transverse mesocolon, sigmoid mesocolon, and mesoappendix

• Mesorectum: Attaches the rectum to the sacrum and posterior pelvic wall

• Other mesenteries: Include the mesogastrium (stomach) and mesoduodenum (first parts of duodenum)

All mesenteric structures arise from the dorsal mesentery during embryological development, except the ventral mesentery of the foregut.

Structure

The mesentery consists of:

• Two layers of peritoneum: Enclosing connective tissue and a loose fatty matrix

• Blood vessels: Including branches of the superior mesenteric artery and vein for the small intestine

• Lymphatic vessels: Important for fat absorption and immune cell trafficking

• Nerves: Derived from the autonomic plexuses to innervate the intestines

• Lymph nodes: Embedded within the mesentery for gut-associated immune response

The mesentery has a root approximately 15 cm long, obliquely oriented from the left upper quadrant (L2) to the right lower quadrant (sacroiliac region).

Function

The mesentery serves several essential functions:

• Suspends the intestine: Anchors the intestines while allowing mobility for peristalsis and digestion

• Supports neurovascular supply: Conveys arteries, veins, lymphatics, and nerves to the intestines

• Maintains gut alignment: Prevents intestinal twisting or volvulus

• Pathway for immune cells: Houses lymph nodes and immune cells involved in gut immunity

Physiological Role(s)

The mesentery contributes to overall digestive physiology through:

• Absorption of nutrients: Transports absorbed nutrients, including fats via lacteals, from the intestines to the bloodstream

• Fat storage: The mesentery contains adipose tissue that serves as an energy reserve and insulator

• Immune surveillance: Lymph nodes filter antigens and coordinate immune responses to pathogens in the gut

• Inflammatory signaling: Plays a role in local inflammatory responses, particularly in diseases like Crohn's

Clinical Significance

The mesentery is involved in various pathological and surgical conditions:

• Mesenteric ischemia: Occlusion of mesenteric arteries can lead to intestinal infarction, a surgical emergency

• Mesenteric lymphadenitis: Enlargement of mesenteric lymph nodes, often due to viral or bacterial infection

• Mesenteric tumors: Includes rare neoplasms like mesenteric fibromatosis or liposarcoma

• Inflammatory bowel disease: In Crohn's disease, mesenteric fat wrapping ("creeping fat") is a hallmark feature

• Internal hernias: May involve mesenteric defects allowing bowel loops to protrude and cause obstruction

• Mesenteric traction syndrome: A perioperative complication characterized by hypotension due to mesenteric manipulation

• Surgical access and resection: Surgeons rely on the mesentery for vascular control in resections, transplants, or anastomoses

Recent reclassification of the mesentery as a continuous organ has implications for surgery, imaging, embryology, and disease understanding. CT and MRI imaging are frequently used to assess mesenteric pathology.