Overview
- Jejunum:
- Wider-bored
- Thicker-walled
- Wall feels ‘double’ (mucous membrane can be felt through muscle wall)
- ‘A shirt sleeve felt through a coat sleeve’
- Coiled in the upper part of the infracolic compartment
- Features taller villi
- Jejunum appears more red than the ileum
- Greater absorptive area than the ileum as it has more circular folds and longer villi
- Ileum:
- Thin wall feels single
- Lower reaches distinguished by presence of Peyer’s Patches on anti-mesenteric border of elongated whitish plaques in the mucous membrane
- Coiled in the lower part of the infracolic compartment and in the pelvis
- Total length varies about 4-6 metres
- 2/5th Jejunum, 3/5th Ileum
Ileal (Meckel’s) Diverticulum
- Present in 2% of the population
- Located 60cm (2 feet) from the Caecum
- Length: 5cm (2 inches)
- True length and location more variable – Meckel’s Diverticulum may be more proximal
- Blind end may contain gastric mucosa or liver or pancreatic tissue
- Represents the intestinal end of the Vitellointestinal Duct
- Apex may be adherent to the umbilicus or connected thereto by a fibrous cord (further remnant of the duct)
Blood Supply
- Jejunal and Ileal branches arise from the left side of the Superior Mesenteric Artery
- Jejunal Branches:
- Join each other in a series of anastomosing loops to form arterial arcades
- Single arcades for the upper jejunum and double lower down
- From arcades, straight arteries pass to the mesenteric border of the gut
- Occlusion of a straight artery may lead to infarction of the segment supplied (end arteries)
- Occlusion of arcade vessels usually inconsequential due to numerous anastomotic connections
- Join each other in a series of anastomosing loops to form arterial arcades
- Ileal Branches:
- Similar but form a larger series of arcades
- 3 to 5
- Most distal lies close to the bowel wall
- Thus, shorter straight arteries
- More fat in the mesentery – windows characteristic of jejunal part are not seen
- Similar but form a larger series of arcades
- Superior Mesenteric Artery
- The end of the artery itself supplies the region of the Ileal Diverticulum (if present)
- Anastomoses with the arcades and with the Ileocolic Branch to supply the Terminal Ileum
Venous Drainage
- Veins all correspond to the arteries and thus drain to the Superior Mesenteric Vein
Lymph Drainage
- Jejunal and Ileal lymph drains to the Superior Mesenteric Nodes via Mural and Intermediate Nodes in the mesentery
Nerve Supply
- Autonomic Nerves reach the small intestinal walls with its blood vessels
- Parasympathetic Vagal Supply
- Augments peristaltic activity
- Augments intestinal secretion
- Many afferent fibres – function uncertain
- Sympathetic Supply:
- From the Lateral Horn Cells of Spinal Segments T9 and T10
- Vasoconstrictor
- Inhibits peristalsis
- Transmits pain signals