Learning Objectives
- Understand the reclassification of the mesentery as a single, contiguous organ.
- Identify the anatomical root and its oblique attachment to the posterior abdominal wall.
- Distinguish between the mobile and fixed (Toldt’s fascia) segments of the mesocolon.
- Master the neurovascular conduits (SMA and IMA) and lymphatic drainage patterns.
- Correlate mesenteric anatomy with clinical pathologies like intestinal volvulus.
Definition and Contemporary Understanding
The mesentery is a double layer of peritoneum that suspends the intestines from the posterior abdominal wall. While previously described as fragmented parts, it is now recognized as a contiguous structure extending from the duodenum to the rectum.
Primary Functions
- Suspension: Anchors the midgut and hindgut while allowing necessary peristaltic movement.
- Neurovascular Conduit: Acts as a protected “highway” for the mesenteric arteries, veins, nerves, and lymphatics.
- Immunological: Contains dense networks of lymph nodes and may play a role in systemic inflammatory diseases.
Anatomical Structure & The “Root.”
The Root of the Mesentery is the narrow, oblique line of attachment to the posterior abdominal wall. It extends from the L2 vertebra (left side) to the Right Sacroiliac Joint.
Regional Subsections
| Subsection | Mobility & Attachment |
|---|---|
| Small Intestine Mesentery | Highly mobile; connects the jejunum and the ileum. |
| Right & Left Mesocolon | Fixed; flattened against the wall via Toldt’s Fascia. |
| Transverse Mesocolon | Mobile; situated between the hepatic and splenic flexures. |
| Mesosigmoid | Mixed; the medial portion is fixed, while the sigmoid portion is mobile. |
| Mesorectum | Anchors the rectum within the pelvic cavity. |
Vasculature & Innervation
The mesentery houses the primary blood supply for the midgut and hindgut.
- Superior Mesenteric Artery (SMA): Travels within the mesentery to supply the Midgut (duodenal papilla to proximal 2/3 of transverse colon).
- Inferior Mesenteric Artery (IMA): Supplies the Hindgut (distal 1/3 of transverse colon to rectum).
- Innervation: Provided by the Superior Mesenteric Plexus, which carries both sympathetic and parasympathetic fibers (vagus nerve) to the viscera.
Lymphatic Drainage
The mesentery is rich in lymph nodes, which are critical for lipid absorption and immune defense.
- Pathway: Inferior Mesenteric Nodes → Superior Mesenteric Nodes → Pre-aortic Lymph Nodes.
Clinical Relevance: Intestinal Volvulus
A volvulus occurs when the bowel twists around its mesenteric axis. This can lead to mechanical obstruction and ischaemic infarction of the bowel tissue.
- Common Site: The Sigmoid Colon (due to its long, mobile mesosigmoid).
- Diagnosis: Often visualized on X-ray as a “coffee bean” sign.
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