Anatomy: Abdomen VI - Small Intestine & Duodenum

duodenum

jejunum

ileum

main function:

absorption of nutrients from ingested materials

• first + shortest (25 cm) part

• widest + most fixed part

• C-shaped course around head of pancreas

• starts @pylorus on right side; ends @duodenojejunal junction on left side

(duodenojejunal flexure = L2 vertebra, 2 - 3 cm L. of midline)

• considered partially retroperitoneal

(mostly fixed by peritoneum to structures on post. ab. wall)

Superior (first) part:

• Short (5 cm); lies anterolateral to body of L1 vertebra

Descending (second) part:

• Longer (7 - 10 cm); descends along right sides of L1 - L3 vertebrae

Horizontal (third) part:

• 6 - 8 cm long + crosses the L3 vertebra

Ascending (fourth) part:

• short (5 cm); begins at left of L3 vertebra + rises superiorly as far as superior border of L2 vertebra

ampulla (duodenal cap)

• first 2 cm of the superior part

(distal 3 cm of the superior part are immobile –> retroperitoneal)

liver + gallbladder

(Peritoneum covers its anterior aspect, but it is bare of peritoneum posteriorly, except for the ampulla)

- hepatoduodenal ligament (part of the lesser omentum) attached superiorly

• greater omentum attached inferiorly

DESCENDING

(lies to right of/parallel to the IVC; curves inferiorly aroudn head of pancreas)

• fusion of bile duct and main pancreatic duct @ major duodenal papilla

• located posteromedially in the descending duodenum

• entirely retroperitoneal

• anterior surface of proximal + distal thirds covered with peritoneum

• peritoneum reflects from middle third = double-layered mesentery of transverse colon = transverse mesocolon

• transversely to the left; passing over the IVC, aorta, + L3 vertebra

• inferior to head of pancreas + uncinate process

• posteriorly = separated from vertebral column by: right psoas major, IVC, aorta, + right testicular or ovarian vessels

• superiorly/along left side of aorta; reaches inferior border of body of pancreas

• curves anteriorly to join the jejunum at the duodenojejunal junction

• ligament of Treitz = supportive suspensory muscle of duodenum

• composed of a slip of skeletal muscle from diaphragm + a fibromuscular band of smooth muscle from 3rd + 4th parts of duodenum

• Contraction = widens angle of duodenojejunal flexure = movement of the intestinal contents

arise from celiac trunk + superior mesenteric artery

celiac trunk:

• supplies duodenum proximal to the entry of the bile duct

• via gastroduodenal artery + branch, superior pancreaticoduodenal artery

Superior Mesenteric Artery:

• supplies the duodenum distal to the entry of the bile duct

• vis its branch = inferior pancreaticoduodenal artery

• lie in the curve b/t duodenum + head of the pancreas

• supply both structures

• anastomosis of superior + inferior pancreaticoduodenal arteries (@level of entry of bile duct), is formed between the celiac + superior mesenteric arteries

–THIS IS THE JUNCTION OF THE EMBRYOLOGICAL FORGUT/MIDGUT–

• proximally, blood supply = celiac trunk

• distally, blood supply = superior mesenteric artery (to L. colic flex.)

• follow the arteries and drain into the portal vein

• some directly, others indirectly (thru superior mesenteric + splenic veins)

• follow the arteries

- anterior lymphatic vessels:

drain into the pancreaticoduodenal lymph nodes (along superior + inferior pancreaticoduodenal arteries) + into pyloric lymph nodes (along gastroduodenal artery)

- posterior lymphatic vessels:

pass posterior to the head of the pancreas, drain into superior mesenteric lymph nodes

- Efferent lymphatic vessels:

drain into celiac lymph nodes

• derive from vagus + greater and lesser (abdominopelvic) splanchnic nerves by way of celiac + superior mesenteric plexuses

• conveyed to the duodenum via periarterial plexuses extending to the pancreaticoduodenal arteries

inflammatory erosions of the duodenal mucosa

• (65%) occur in posterior wall of superior part, within 3 cm of pylorus

• occasionally, ulcer perforates duodenal wall = permitting contents to enter peritoneal cavity = peritonitis

(ex. erosion of the gastroduodenal artery = severe hemorrhage +peritonitis)

liver

gallbladder

pancreas

• two or three inconstant folds + fossae around duodenojejunal junction

• paraduodenal fold + fossa = large and lie to left of ascending part of duodenum

If a loop of intestine enters this fossa, it may strangulate

• resuires surgical repair; do not injure branches of inferior mesenteric artery + vein or ascending branches of left colic artery (associated with fold)