Small intestine

• Duodenum

  • First, shortest (25cm), widest and most fixed part of small intestine, connecting stomach to jejunum
  • Begins at pylorus, has a C-shaped course around head of pancreas and ends at duodenojejunal junction (flexure)

  
• Parts and flexures of duodenum

  • 1st part aka superior part
  • 2nd part aka descending part
  • 3rd part aka inferior/horizontal part
  • 4th part aka ascending part

  Flexures

  Superior duodenal flexure

  Inferior duodenal flexure

  Duodenojejunal flexure

  
• First part of duodenum: 5cm

  • Begins at pylorus
  • Lies anterolateral to body of L1
  • Retroperitoneal: lies against post abdominal wall
  • Anterior relations: quadrate lobe of liver, gallbladder
  • Posterior relations: gastroduodenal artery, head of pancreas, bile duct, portal vein

  
• Second part of duodenum

  • 7-10cm long
  • Begins at superior duodenal flexure and descend along right side of l1,l2 and L3 where it curves towards inferior duodenal flexure to become continuous with 3part
  • Anterior relations: right lobe of liber, transverse colon
  • Posterior relations: right kidney, right renal vessels, right edges of inferior vena cava

  Inside the 2 part of duodenum we can see

  • major duodenal papille: elevation where common bile duct and pancreatic ducts opens
  • Minor duodenal papillae: opening of accessory pancreatic duct

  
• Major and minor duodenal papillae

  • The bile duct unites with the main pancreatic duct to form the hepatopancreatic ampulla that opens at the major duodenal papilla on the posteromedial wall of the descending part of duodenum .
  • The major duodenal papilla is surrounded by circular muscle fibers called the sphincter of Oddi .
  • The accessory pancreatic duct opens at the minor duodenal papilla on the posteromedial wall of the descending part of duodenum superior to the major duodenal papilla .

  
• Third part of duodenum

  • 6-8cm long
  • begins at inferior duodenal flexure crosses L3 vertebra from right to left ends by joining with 4th part in front of abdominal aorta
  • Anterior relations: superior mesenteric vessels + root of mesentery
  • Posterior relations: right ureter, right psoas major, inferior vena cava, abdominal aorta, right gonadal vessels.
• fourth part of duodenum

  • 5cm long
  • runs upwards on left of aorta up to the upper border of L2 where it turns forwards to become continuous with jejunum at duodenojejunal flexure.
  • Anterior relations: transverse colon + mesocolon
  • Posterior relations: left sympathetic chain, left gonadal artery, inf mesenteric veins,
• Relations of duodenum with peritoneum

  1. Proximal 2cm of superior part is intraperitoneal and mobile. Its called duodenal ampula and gives attachment superiorly to hepatoduodenal ligament of lesser omentum and inferiorly to to gastrocolic ligament of greater omentum.
  2. distal 3cm of superior part and rest of duodenum is retroperitoneal and immobile.

  
• Duodenum


  Here

  
• Suspensory muscle of duodenum: ligament of treitz

  • Arises from right crus of diaphragm
  • passes anterior to left renal vein and posterior to pancreas and splenic vein
  • Inserts into duodenojejunal flexure
  • widens the angle of duodenojejunal flexure, facilitating movement of intestinal contents

  
• Suspensory ligament of duodenum

  Here

  
• Arterial supply of duodenum

  The arteries of the duodenum arise from the celiac trunk and the superior mesenteric artery .

  Proximal to major duodenal papillae

  • Superior pancreaticoduodenal artery (celiac trunk)

  Distal to major duodenal papillae

  • Inferior pancreaticoduodenal artery (superior mesentery a.)
• Lymphatic drainage of duodenum

  • Pancreaticoduodenal lymph nodes
  • Puloric lymph nodes
  • superior mesenteric lymph nodes
  • All of them drain into celiac Lymph nodes
• Innervation of duodenum

  • Parasympathetic: vagus mn
  • Sympathetic: thoracic and lumbar splanchinc nerves
  • Enteric nervous system
• Venous drainage of duodenum

  • SUPERIOR PANCREATICODUODENAL VEIN
  • inferior pancreaticoduodenal vein

  all drain into, splenic, superior mesenteric and hepatic portal vein
• small intestine

  • Hallow, convoluted tube of approximately 5-7m in length extending from pylorus to ileocecal junction.
  • Completes digestion + absorption of products
  • 3 segments: duodenum, jejunum and ileum.

  
• distinct features of small intestine

  Luminal surface of small intestine is modified to increase its surface area: plica circularis, villi and microvilli.

  • Plica circularis: transverse folds of mucosa forming semicircular elevations; found predominantly in distal duodenum and proximal jejunum. Increase surface area by 2/3 folds
  • Vili: finger-like projections of intestinal mucosa. They increase suf area. Btw villi are crypts of lieberkuhn that secrete intestinal juice.
  • Microvilli: cylindrical protrusions on apical surface of enterocytes.
• Jejunum

  • Middle section of small intestine
  • Starts at duodenojejunal flexure there is no clear demarcation btw jejunum and ileum.
  • 2.5m; lies in upper left quadrant
  • Entirely intraperitoneally has mesentery proper attaching it to posterior abdominal wall
  • Has more prominent circular folds
  • Wall is thicker, redder in color, wider lumen

  
• Ileum

  • final and longest segment of small intestine
  • extends from jejunum to ileocecal junction, where ileum invaginates into cecum to form ileocecal valve.
  • In right lower quadrant, terminal ileum can extend into pelvic cavity
  • narrower lumen, thinner wall, less prominent circular folds
  • Intraperitoneally
  • At ileocecal junction, lamina muscularis of ileum protrudes into lumen of cecum forming ileocecal fold: these muscular fibers form a muscular ring the ileocecal sphincter that controls emptying of small intestine contents into large intestine

  
• Blood supply of small intestine

  • Jejunum and ileum are supplied by branches of superior mesenterif artery: jejunal + ileal arteries. These anastomose with each other forming arterial arcades (loop) which send straight arteries (vasa recta) to jejunum and ileum. These runs along mesentery.

  
• venous drainage pf small intestine

  • Jejunal + ileal veins: these drain into superior mesenteric vein than into portal vein.
• Nerve supply of small intestine

  • The small intestine is innervated by branches of the vagus nerve (CN X) and thoracic splanchnic nerves. Their nerve branches extend throughout the entire length of the small intestine in the form of two plexuses:
  • Submucosal plexus (of Meissner) found in the submucosa of the small intestine and contains only parasympathetic input from the vagus nerve (CN X)
  • Myenteric plexus: located in the muscularis externa of the small intestine, contains both sympathetic and parasympathetic nerve fibers
• • Parasympathetic input to small intestine increases intestinal motility and peristalsis, enhances blood flow to intestine and stimulate secretion of digestive enzymes and fluids.
  • Sympathetic input to small intestine decreases motility and peristalsis, constrict blood vessels decreasing blood flow and inhibits secretion of digestive fluid and enzymes
• Duodenum duodenum

  
• Small intestine- jejunum or ileum

  
• Small intestine slide

  
• Duodenum slide

  
• Duodenum slide description

  
• Small intestine slide description