Abdomen VI - Small Intestine & Duodenum

Question 1

SMALL INTESTINE

• 3 parts
• main function

Answer 1

duodenum

jejunum

ileum

main function:

absorption of nutrients from ingested materials

Question 2

DUODENUM

Answer 2

• 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) **

Question 3

4 parts of the DUODENUM

Answer 3

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

Question 4

Which part of the duodenum has a mesentery and is mobile?

Answer 4

ampulla (duodenal cap)

• first 2 cm of the superior part

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

Question 5

superior part of the duodenum ascends from the pylorus and is overlapped by what structures?

Answer 5

liver + gallbladder

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

Question 6

The proximal part of the superior duodenum has what 2 structures attached to it?

Answer 6

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

• greater omentum attached inferiorly

Question 7

The bile and main pancreatic ducts enter the posteromedial wall of whiche duodenal section?

Answer 7

DESCENDING

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

Question 8

hepatopancreatic ampulla

Answer 8

• fusion of bile duct and main pancreatic duct @ major duodenal papilla
• located posteromedially in the descending duodenum

Question 9

DESCENDING DUODENUM

Answer 9

• entirely retroperitoneal
• anterior surface of proximal + distal thirds covered with peritoneum
• peritoneum reflects from middle third = double-layered mesentery of transverse colon = transverse mesocolon

Question 10

HORIZONTAL DUODENUM

Answer 10

• 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

Question 11

ASCENDING DUODENUM

Answer 11

• 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

Question 12

Ligament of Treitz

Answer 12

• 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

Question 13

arteries of the duodenum

Answer 13

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

Question 14

pancreaticoduodenal arteries

Answer 14

• 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.)

Question 15

veins of the duodenum

Answer 15

• follow the arteries and drain into the portal vein
• some directly, others indirectly (thru superior mesenteric + splenic veins)

Question 16

lymphatic vessels of the duodenum

Answer 16

• 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

Question 17

nerves of the duodenum

Answer 17

• 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

Question 18

Duodenal (peptic) ulcers

Answer 18

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)

Question 19

Which structures may become adherent to the inflamed duodenum and also become ulcerated as the lesion continues to the tissue that surrounds it?

(due to close proximity)

Answer 19

liver

gallbladder

pancreas

Question 20

Paraduodenal Hernias

Answer 20

• 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)