Anatomy: Abdomen VII - Jejunum & Ilium

• begins at duodenojejunal flexure (alimentary tract resumes an intraperitoneal course)

• jejunum + ileum = 6 - 7 m long (jejunum constituting 2/5)

• most of jejunum lies in left upper quadrant of the infracolic compartment

• Jejunum + ileum = 6-7m long (ilium consists of 3/5)

• most of the ileum lies in the right lower quadrant

- ends at ileocecal junction (union of terminal ileum + cecum)

(no clear line of demarcation)

• Jejunum = site of digestion processes + secretion of enzymes continue

• ileum = more fat inside the mesentery

• ileum = abundant mucosa associated lymph tissue (MALT)

Peyer’s patches

fan-shaped fold of peritoneum; attaches jejunum + ileum to posterior abdominal wall

• origin = (approximately 15 cm long) directed obliquely, inferiorly, and to the right

• extends from duodenojejunal junction (L. of vertebra L2) to ileocolic junction + right sacroiliac joint

• average width of mesentery (root to intestinal border) = 20 cm

• root of mesentery crosses (successively) the ascending + horizontal parts of duodenum, abdominal aorta, IVC, right ureter, right psoas major, and right testicular or ovarian vessels.

superior mesenteric vessels

lymph nodes

variable amount of fat

autonomic nerves

supplies the jejunum + ileum

• usually arises from abdominal aorta at L1 vertebra level

(approx 1 cm inferior to celiac trunk)

• runs b/t layers of mesentery, sending 15 - 18 branches to the jejunum + ileum

• arteries unite to form loops or arches = arterial arcades

(give rise to straight arteries = vasa recta)

drains jejunum + ileum

• lies anterior + to the right of superior mesenteric artery in the root of the mesentery

• ends posterior to the neck of the pancreas, where it unites with the splenic vein to form the portal vein

• specialized lymphatic vessels in the intestinal villi

• absorbe fat

• empty their milk-like fluid into lymphatic plexuses in the walls of the jejunum + ileum

• drain in turn into lymphatic vessels between the layers of the mesentery

Juxta-intestinal lymph nodes: located close to the intestinal wall

Mesenteric lymph nodes: scattered among the arterial arcades

Superior central nodes: located along the proximal part of the superior mesenteric artery

• Efferent lymphatic vessels from mesenteric lymph nodes drain to the superior mesenteric lymph nodes

• Lymphatic vessels from terminal ileum follow ileal branch of the ileocolic artery to ileocolic lymph nodes

Sympathetic:

• origin: T8 - T10 segments of spinal cord; reach the superior mesenteric nerve plexus through the sympathetic trunks + thoracic abdominopelvic (greater, lesser, and least) splanchnic nerves

Parasympathetic:

• derive from the posterior vagal trunks

- presynaptic parasympathetic fibers synapse with postsynaptic parasympathetic neurons in the myenteric and submucosal plexuses in the intestinal wall

… reduces motility of intestine + secretion; acts as a vasoconstrictor

• reducing/stopping digestion + making blood (and energy) available for an emergency situation

… increases motility of intestine + secretion, restoring digestive activity following a sympathetic reaction

* also has sensory (visceral afferent) fibers; insensitive to most pain stimuli, including cutting and burning; it is sensitive to distension that is perceived as colic (spasmodic abdominal pains).

foregut derivatives:

esophagus, stomach, pancreas, duodenum, liver, and biliary ducts localizes in the epigastric region

midgut derivatives:

small intestine distal to bile duct, cecum, appendix, ascending colon, and most of the transverse colon

localizes in the periumbilical region

hindgut derivatives:

distal part of the transverse colon, descending colon, sigmoid colon, and rectum

localizes in the hypogastric region.

• usually occurs around 6-8 weeks of development

• bowel returns to abdominal cavity by weeks 10 - 11

• rapidly growing midgut (supplied by superior mesenteric a.) is physiologically herniated into proximal part of umbilical cord

• attached to the yolk sac by the yolk stalk

• as it returns to abdominal cavity, midgut rotates 270° around axis of superior mesenteric artery

• as relative size of liver + kidneys decreases, midgut returns to the abdominal cavity as increased space becomes available

• results in several congenital anomalies such as volvulus (twisting) of the intestine

• Occlusion of vasa recta by emboli = ischemia of part of the intestine concerned

• if severe, necrosis of the involved segment results and ileus (obstruction of the intestine) of the paralytic type occurs

• Ileus accompanied by a severe colicky pain, along with abdominal distension, vomiting, and often fever + dehydration

• early detection = surgical clearing of vessel

ileal diverticulum (of Meckel) = congenital anomaly in 1 - 2% of population

- remnant of proximal part of embryonic yolk stalk; diverticulum usually appears as a finger-like pouch

• always at site of attachment of the yolk stalk on the antimesenteric border (opposite mesenteric attachment) of the ileum

• usual location: infants = 30-60cm fr. ileocecal junction; adults = 50cm

• may be free (74%) or attached to umbilicus (26%)

• may include areas of acid-producing gastric tissue, pancreatic tissue, or jejunal or colonic mucosa

• may become inflamed + produce pain mimicking appendicitis

• gastric tissue = peptic ulcer may occur here