lecture 8 part 3 - small intestine

Question 1

Small intestine position

Answer 1

• Left upper and right lower quadrants
• Infracolic compartment: extends into pelvis

Question 2

the small intestine is

Answer 2

intraperitoneal

Question 3

Divisions and features of small intestine

Answer 3

• Duodenum
• Jejunum
  - Proximal 2/5ths of small intestine from duodenojejunal junction
• Ileum
  - Distal 3/5ths of the small intestine ending at the ileocaecal junction

Question 4

Duodenum

Answer 4

• Whole duodenum (excluding 1st part) lies retroperitoneally
• Common bile duct + pancreatic duct = common opening on medial aspect of 2nd part of duodenum
  → Opening on major duodenal papilla, controlled by sphincter of Oddi
• Suspensory ligament of duodenum (Ligament of Treitz) – extends from R crus of diaphragm to suspend duodenojejunal juncture
• Divided into 4 parts

Question 5

Question 6

first part of duodenum

Answer 6

• – 1st part is 5cm from gastroduodenal junction
• – Anterior: liver, gall bladder, L1 vertebral body
• – Posterior: portal vein, bile duct
• – On transpyloric line (L1)

Question 7

second part of duodenum

Answer 7

• Vertical 7.5cm that curves around head of pancreas
• Ascends along the right sides of L1-L3
• Anterior: transverse colon
• Posterior: R kidney, ureter, R suprarenal gland
• Posteromedial: major & minor duodenal papillae and head of pancreas

Question 8

third part of duodenum

Answer 8

• Horizontal 6-8cm
• Crosses the body of L3
• Transverse 10cm to the L
• Anterior: mesentery of small intestine
• Posterior: inferior vena cava, abdominal aorta
• Superior: head of pancreas

Question 9

fourth part of duodenum

Answer 9

• Runs vertical for 2.5 - 5cm to duodenojejenal junction
• Begins at the left of L3
• Rises superior as far as the superior border of L2
• Suspensory ligament of duodenum (Lig. of Treitz) extend from right crus of diaphragm
• Suspends duodenojejunal junction

Question 10

Jejunum versus Ileum

Answer 10

Jejunum
* – Larger diameter
* – Greater surface for digestion
* – Thicker wall
* – Less vascular arcades present
* – Thinner mesentery with less fat
* – Many large, tall mucosal folds
* – Less lymphoid tissue
* – Vasa recta long, large loops

Ileum
– Smaller diameter
– Smaller surface for digestion
– Thinner wall
– More vascular arcades present
– Thicker mesentery with more fat
– Less low, sparse mucosal folds
– More lymphoid tissue
– Vasa recta short, short loops

Question 11

Blood supply:

Answer 11

Besides the inferopancreaticoduodenal that forms an anastomosis with the superior pancreaticoduodenal artery from the celiac trunk
Superior mesenteric artery
* Jejunal and ileal branches form arterial arcades which give vasa recta

Question 12

Lymphatic drainage

Answer 12

• Superior mesenteric lymph nodes (part of midgut)
• Mesenteric lymph nodes, juxtaintestinal lymph nodes
• Ileocolic lymph nodes
• These 3 first drains the lymph before it enters the superior mesenteric lymph nodes

Question 13

Small intestine: Innervation

Answer 13

• Sympathetic (T9-12) NOTE: change in roots
• Sympathetic trunks
• Greater, lesser and least splanchnic nerves
• To the superior mesenteric (and coeliac) plexus * Pain
• Acts as a vasoconstrictor – makes food available for fight or flight reflex

Parasympathetic
* Posterior vagal trunk
* Motor
* Increases motility and secretion of intestine
* Restores digestive activity following a sympathetic reaction