Download JEJUNUM AND ILEUM Jejunum begins at the duodenojejunal flexure

JEJUNUM AND ILEUM









Jejunum begins at the duodenojejunal flexure where the digestive tract resumes an
intraperitoneal course
Ileum ends at ileocecal junction
Jejunum makes of 2/5ths of the length, while ileum makes of 3/5ths of intraperitoneal section of
the small intestine
Most of jejunum lies in right upper quadrant, while most of ileum lies in right lower quadrant
Mesentery is a fold of peritoneum that attaches the jejunum and ileum to the posterior
abdominal wall
o Origin of the root of the mesentery is directed obliquely, inferiorly, and to the right
o Extends from duodenojejunal junction on the left side of L2 to the ileocolic junction and
the right sacroiliac joint.
ARTERIES
o Superior mesenteric artery supplies jejunum and ileum via jejunal and ileal arteries
 Arises from abdominal aorta at the level of L1, 1 cm inferior to the celiac trunk,
and runs between the layers of the mesentery, sending 15-18 branches to the
jejunum and ileum
 Arteries unite to form loops or arches, called arterial arcades, which give rise to
straight arteries, called vasa recta
VEINS
o Superior mesenteric vein drains the jejunum and ileum
 Lies anterior and to the right of the SMA in the root of the mesentery
 Ends posterior to the neck of the pancreas, where it unites with the splenic vein
to form hepatic portal vein
Intestinal villi absorb fat lacteals
o Lymph nodes involved are juxta-intestinal lymph nodes—located close to intestinal wall
o Mesenteric lymph nodes—scattered among the arterial arcades
o Superior central nodes—located along the proximal part of the SMA
NERVES
o SMA and its branches are surrounded by a periarterial nerve plexus through which
nerves are conducted to the parts of the intestine supplied by the artery
o Sympathetics to jejunum and ileum come from T8-T10 segments of the spinal cord and
reach superior mesenteric nerve plexus through the sympathetic trunks and thoracic
abdominopelvic (greater, lesser, and least) splanchnic nerves
 Presynaptics synapse in celiac and superior mesenteric (prevertebral) ganglia
 Reduces peristaltic and secretory activity of intestine and acts as a
vasoconstrictor
o Parasympathetics derived from posterior vagal trunks
 Presynaptics synapse with post-synaptic parasympathetic neurons in the
myenteric and submucosal plexuses in the intestinal wall
 Increases peristalsis and secretion
o
o
Also has sensory/visceral afferent fibers
Intestine is insensitive to most pain, but it is sensitive to distension that is perceived as
colic (spasmodic abdominal pains or “intestinal cramps”)
LARGE INTESTINE




Absorbs water and stores feces
Consists of cecum; appendix; ascending, transverse, descending, sigmoid colon; rectum; anal
canal
Can be distinguished from small intestine by
o Omental appendices
 Small fatty omentum like projections
o teniae coli
 3 longitudinal bands
 Mesocolic tenia—transverse and sigmoid colon attach
 Omental tenia—omental appendices attach
 Free tenia—neither mesocolons nor omental appendices are attached
 They begin at the base of the appendix as the thick longitudinal layer of the
appendix separates into 3 bands
 They run the length of the large intestine, abruptly broadening and merging
with each other again at the rectosigmoid junction into a continuous
longitudinal layer around the rectum
 Contractions of these form the haustra
o Haustra
 Sacculations of the wall of the colon between the teniae
o It’s just larger than the small intestine.
CECUJM AND APPENDIX
o Cecum is the first part of the large intestine—continuous with ascending colon
 Is a blind intestinal pouch
 Lies in the iliac fossa of the right lower quadrant of the abdomen, inferior to the
junction of the terminal ileum and cecum
 May be palpable through the anterolateral abdominal wall if distended with gas
or feces
 Lies close to inguinal ligament
 Almost entirely enveloped by peritoneum, but has no mesentery
 Commonly bound to lateral abdominal wall by one or more cecal folds of
peritoneum
 Terminal ileum enters the cecum obliquely and partly invaginates into it
 Ileal orifice enters cecum between ileocolic lips (superior and inferior)
 Folds that meet laterally forming ridges called the frenula of the ileal
orifice
 Is usually closed, appearing as ileal papilla on the cecal side
o
o
o
o
Appendix is a blind intestinal diverticulum that contains masses of lymphoid tissue
 Is on the posteromedial aspect of cecum, inferior to the ileocecal junction
 Has short triangular mesentery, the mesoappendix, which derives from the
posterior side of the mesentery of the terminal ileum
 Attaches to the cecum and proximal part of appendix
 Position of the appendix is variable, but it is usually retrocecal
ARTERIAL SUPPLY
 Ileocolic artery, terminal branch of the SMA
 Appendicular artery, branch of ileocolic artery, supplies the appendix
VENOUS DRAINAGE
 Tributary of SMV, the ileocolic vein
NERVES
 Superior mesenteric plexus
 Sympathetic fibers are from lower thoracic part of spinal cord
 Afferent nerve fibers accompany these to T10 spinal segment
 Parasympathetics are from vagus nerves