Small Bowel Anatomy Lecture PDF

Anatomy – MED 106  The Basics ❖ Longest portion of the digestive system ❖ Continuation of the stomach, ends at right colon ❖ 3 portions ❖ Duodenum ❖ Jejunum ❖ Ileum ❖ Function: Ingredients absorption  The Basics Pyloric orifice...

Anatomy – MED 106  The Basics ❖ Longest portion of the digestive system ❖ Continuation of the stomach, ends at right colon ❖ 3 portions ❖ Duodenum ❖ Jejunum ❖ Ileum ❖ Function: Ingredients absorption  The Basics Pyloric orifice ? Ileocecal valve The Basics  The Duodenum ❖ First portion of the small bowel ❖ Approximately 25 cm long ❖ Borders ❖ Pylorus ❖ Duodenojejunal flexion  The Duodenum ❖ C – shaped (head of pancreas inside C) ❖ Retroperitoneal ❖ Four portions ❖ 1st portion: Superior ❖ 2nd portion: Descending ❖ 3rd portion: Horizontal ❖ 4th portion: Ascending  The Duodenum Position ❖ Behind stomach & large intestine ❖ Forms lateral wall of lesser peritoneal cavity  The Duodenum 1st portion Superior portion (1st) ❖ Lateral to body of L1 ❖ Length: 5 cm ❖ Ampulla (duodenal cap) ❖ Intraperitoneal at its beginning  The Duodenum 1st portion Superior portion (1st) ❖ Anterior: Quadrate lobe of liver, gallbladder ❖ Posterior: Bile duct, gastroduodenal artery, portal vein ❖ Superior: Epiploic forame ❖ Inferior: Head of pancreas  The Duodenum 2nd portion Descending portion (2nd) ❖ Lateral to body of L1-L3 ❖ Length: 7.5 cm ❖ Major duodenal papilla (Vater’s) ❖ Retroperitoneal  The Duodenum 2nd portion Descending portion (2nd) ❖ Anterior: Right lobe of the liver, transverse colon ❖ Posterior: Right kidney and vessels, IVC ❖ Lateral: Right colic flexure ❖ Medial: Head of pancreas The Duodenum 2nd portion  The Duodenum 2nd portion Right kidney Right lobe of liver IVC Transverse colon  The Duodenum 2nd portion Major duodenal papilla: ❖ Common ending of common bile duct and pancreatic duct ❖ Posterior – medial wall of 2nd portion of duodenum  Common bile duct ends in the 2nd portion of duodenum ampulla of Vater  Ampulla of Vater Open into lumen of duodenum by means of the major Sphincter duodenal papilla of Oddi halfway down 2nd portion of duodenum ampulla surrounded by sphincter of the hepatopancreatic ampulla (sphincter of Oddi)  The Duodenum Ductal system (short) ❖ Common bile duct: Transfers bile from liver to duodenum (fat emulsification) ❖ Pancreatic duct: Transfers pancreatic enzymes to duodenum (digestion)  The Duodenum 3rd portion Horizontal portion (3rd) ❖ Runs horizontally in front of L3 ❖ Length: 10cm ❖ Retroperitoneal  The Duodenum 3rd portion Horizontal portion (3rd) ❖ Anterior: Transverse mesocolon, SMA, SMV ❖ Posterior: IVC, abdominal aorta, right ureter ❖ Superior: Head of pancreas ❖ Inferior: Peritoneal cavity  The Duodenum 4th portion Ascending portion (4th) ❖ Left side of L2 ❖ Length: 2.5cm ❖ Retroperitoneal ❖ Suspended by the ligament of Treitz  The Duodenum 4th portion Ascending portion (4th) ❖ Anterior: Peritoneal cavity ❖ Posterior: Left crus of diaphgragm, inferior mesenteric vein ❖ Superior: Body of pancreas ❖ Inferior: Peritoneal cavity  The Duodenum Ligament of Treitz ❖ Suspensory ligament between right crus of the diaphragm and 4th portion of duodenum ❖ Creates duodenojejunal flexure ❖ Marks the border between upper and lower gastrointestinal system  Arterial vascularization of duodenum Gastroduodenal artery Hepatic artery Right gastric Anterior superior Posterior superior artery pancreatoduodenal pancreatoduodenal artery artery Right Celiac artery Left gastric gastroepiploic artery artery Posterior inferior Short gastric Anterior inferior Left pancreatoduodenal arteries pancreatoduodenal gastroepiploic artery artery artery Splenic artery Superior mesenteric artery  Venous drainage of the duodenum Right + left gastric vein = Coronary vein Short gastric veins Portal vein. Anterior superior pancreaticoduodenal RGEV. Left gastroepiploic vein Posterior superior pancreaticoduodenal vein Splenic veins Anterior inferior Posterior inferior Superior pancreaticoduodenal pancreaticoduodenal mesenteric vein vein vein  Venous drainage ❖ Same named veins drain into portal system  The Duodenum Lymphatics Lymphatics ❖ Pancreaticoduodenal lymph nodes (anterior) ❖ Pyloric lymph nodes (anterior) ❖ Superior mesenteric lymph nodes (posterior) ❖ Celiac lymph nodes  Jejunum & Ileum General ❖ Intraperitoneal ❖ Extends rom the duodenojejunal flexure to the ileocecal junction ❖ No clear transition between jejunum and ileum ❖ Jejunum 2/5 (in LUQ) and ileum 3/5 (in RLQ) ❖ Length of 6-7m (in cadavers)  Jejunum & Ileum Differences Jejunum Ileum Color Deeper red Pale pink Diameter Wider Small Wall Thicker Thinner Vasa recta Long Short Mesentery Less fat More fat Lymph nodes Few Many  Jejunum & Ileum Mesentery ❖ Fan shaped peritoneal fold ❖ Attaches/suspends small intestine to posterior abdominal wall ❖ Contains superior mesenteric vessels, lymphatics, nerves Small intestine mesentery  Basic arrangement Abdominal wall Retroperitoneum Parietal peritoneum Visceral peritoneum Retroperitoneal organ Intraperitoneal organ Mesentery  Peritoneal formations Mesentery Double layer of peritoneum enveloping the vessels, nerves and lymph nodes supplying the viscera ❖ Small intestine mesentery ❖ Transverse and sigmoid mesocolons ❖ Mesoesophagus ❖ Mesogastrium ❖ Mesoappendix  Root of mesentery ❖ Extends from duodenojejunal flexure to ileocolic junction ❖ Olique, inferior and to the right  Jejunum & Ileum Vascularization Arteries ❖ Superior mesenteric artery ❖Jejunal arteries ❖Ileal arteries ❖Anastomotic arterial arcades → Vasa recta  Arterial vascularization of small bowel Gastroduodenal artery Hepatic Jejunal artery arteries Ileal arteries Right gastric Anterior superior Posterior superior artery pancreatoduodenal pancreatoduodenal artery artery Right Left gastric gastroepiploic Ileocecal artery Celiac artery artery artery Posterior inferior Short gastric Anterior inferior Left pancreatoduodenal arteries pancreatoduodenal gastroepiploic artery artery artery Splenic artery Superior mesenteric artery Jejunum & Ileum Vascularization  Jejunum & Ileum Vascularization Jejunum Ileum Arcades Single row Many rows Vasa recta Longer Shorter Density High Low  Jejunum & Ileum Vascularization Small bowel veins ❖ Jejunal veins ❖ Ileal veins ❖ Ends at superior mesenteric vein → Portal vein  Venous drainage of the small bowel Right + left gastric vein = Coronary vein Short gastric veins Portal vein. Anterior superior pancreaticoduodenal RGEV. Left gastroepiploic vein Jejunal veins Posterior superior pancreaticoduodenal Ileal veins vein Splenic veins Anterior inferior Posterior inferior Superior pancreaticoduodenal pancreaticoduodenal mesenteric vein vein vein  Lymphatics of the small bowel Lymphatics ❖ Lymphatics in the intestinal villi Cysterna chyli Para- (lacteals) aortic lymph ❖ Lymphatic plexuses nodes Superior mesenteric ❖ Lymph nodes lymph nodes Superior ❖Juxta-intestinal lymph nodes central lymph nodes ❖Ileocolic lymph nodes Mesenteric lymph ❖Mesenteric lymph nodes Ileo-colic nodes lymph ❖Superior central lymph nodes Juxta- nodes intestinal lymph nodes ❖ To Cysterna chyli => Thoracic duct  Innervation of the small bowel Enteric nervous system Sympathetic Parasympathetic innervation innervation Bowel motility  The enteric nervous system Two interconnected Plexuses within the walls of the gastrointestinal tract Myenteric plexus Submucous plexus  The enteric nervous system > Each plexus is formed by: ganglia + bundles of nerve fibers. Sensory and motor neurons within the enteric system control reflex activity within the gastrointestinal system. These reflexes regulate peristalsis, secretomotor activity, and vascular tone. These activities can occur independently of the brain and spinal cord Can also be modified by input from parasympathetic and sympathetic fibers (Sensory information from the enteric system is carried back to the CNS by visceral sensory fibers).  Enteric System ❖ Enteric nervous plexuses initiate and end bowel activity ❖ Can function independently of central nervous system ❖ Contain more neurons than the spinal cord  Enteric innervation Parasympathetic Posterior vagal n. Enteric plexus T8-T10.. Sympathetic Superior mesenteric g.. Major, lesser, least splachnic nerve. ❖ Parasympathetic accelerates bowel motily ❖ Sympathetic slows down bowel motility Surface anatomy