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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