Part 4: Vessels and Nerves of the Gut

Question 1

Where do the 3 embryonic vessels that supply the gut pass and what vessels are they known as in the developed individual?

Answer 1

Dorsal mesogastrium - supplies foregut - becomes coeliac
Dorsal mesentery - supplies midgut - becomes superior mesenteric
Dorsal mesocolon - supplies hingut - becomes inferior mesenteric

Question 2

What is the lymph drainage system of the gut?

Answer 2

From mucosal lymphoid follicles to local nodes (eg paracolic) to deep nodes (eg para-aortic) to drain via coeliac nodes into ciserna chyli

Question 3

When does herniation of the gut occur in development?

Answer 3

Week 6 to 10 as the growth of the gut outstrips the abdominal cavity.

Question 4

What vessel supplies herniated gut during development and what is the apex of the hernia?

Answer 4

SMA. Only midgut is herniated.

Apex is site of vitellointestinal duct

Question 5

Describe how herniation of the gut in development relates to the final position of the gut?

Answer 5

The hernia rotates anticlockwise on the axis of SMA so that distal loop is anterior to proximal. Thus SMA branches to proximal gut arise on L and branches to distal gut arise from R

Question 6

How does growth of the liver affect its relation to falciform ligament and ligament teres?

Answer 6

Liver outstrips ventral mesogastrium by growing caudally. Thus causes a notch inferiorly by ligamentum teres. Superiorly falciform ligament forms triangular ligament after liver grows superiorly peeling apart L + R layers.

Question 7

What are the boundaries of foregut, midgut and hindgut?

Answer 7

Foregut: lower oesophagus to bile duct opening
Midgut: Bile duct opening to just proximal to splenic flexure
Hindgut: Splenic flexure to upper 1/3 anal canal

Question 8

What vertebral level does coeliac trunk arise and what are its bifurcations?

Answer 8

T12
Common hepatic
L gastric
Splenic

Question 9

What is the cause and divisions of common hepatic artery?

Answer 9

Divides into hepatic (to liver) and R gastric and gastroduodenal arteries.
R gastric to lesser curvature via lesser omentum at distal end of stomach
Gastroduodenal becomes superior pancreaticoduodenal (head of pancreas and duodenum to bile duct) and R gastroepiploic artery passing to greater curvature stomach via greater omentum at disal end

Question 10

Describe the course and branches of splenic artery

Answer 10

Passes to L from trunk, tortuous path. Gives short gastric branches to fundus and L gastroepiploic artery to greater curvature/omentum. Runs in lienorenal ligament to supply spleen after running across hilum L kidney

Question 11

What vertebral level does SMA branch off aorta? What are its major branches?

Answer 11

L1
Inferior pancreaticoduodenal - duodenum and head of pancreas, may come of R hepatic
Jejunal and ileal branches - form anastomosing arcades
Ileocolic artery - Ileocolic region, gives ileal branch that anastomoses with terminal SMA
R colic - Ascending colon
Middle Colic - Hepatic flexure and transverse colon

Question 12

What is the large avascular window sometimes used to access lesser sac and posterior wall of stomach by surgeons?

Answer 12

From middle colic to L colic artery in transverse mesocolon. Colon is supplied by anastomosis of the two arteries running close to bowel

Question 13

Describe the venous drainage of the midgut

Answer 13

Each branch of SMA is accompanied by a vein which all flow into SMV

Question 14

Describe the venous drainage of foregut

Answer 14

Very similar to arterial supply but no gastroduodenal vein.
Splenic vein unites with SMV behind pancreas to form portal vein which drains to liver.
R gastroepiploic joins directly to SMV
L gastric vein empties directly to portal vein

Question 15

What is the vertebral level of IMA branch from aorta? What is its supply?

Answer 15

L3/umbilicus

Hindgut - from spenic flexure to anal canal

Question 16

Describe the course of the IMA?

Answer 16

Runs obliquely down to pelvic brim crossing it at bifurcation of L common iliac vessels over SIJ. At this point converges with ureter. In its course it lies on aorta, L psoas muscle, sympathetic trunk, L common iliac artery and hypogastric nerve

Question 17

What are the branches of IMA?

Answer 17

Gives rise to L colic, 3-4 sigmoid arteries and becomes superior rectal artery after crossing over pelvic brim

Question 18

What is the venous drainage of the hindgut?

Answer 18

Same as arterial system - drains via arteries to IMV which empties into splenic vein.
Inferior rectal vein drains to systemic system not portal

Question 19

What is the lymph drainage of the hindgut?

Answer 19

Starts as lymphoid follicles (eg peyer’s patches). Drains to nearby nodes - eg para colic. These drain alongside major blood vessels to pre-aortic groups. Eventually reaches cisterna chyli.

Question 20

What is the myenteric plexus?

Answer 20

Also known as Auerbach’s plexus. Situated between the two muscle layers of the gut (longitudinal and circular layers). Forms part of enteric nervous system

Question 21

What is the submusoca plexus?

Answer 21

Also known as Meissner’s plexus. Scattered ganglion making upsubmucosal plexus. Part of enteric nervous system.

Question 22

What is unique in regards to the enteric nervous system function?

Answer 22

Although all parts are supplied by sympathetic (post ganglionic inhibitory) and parasympathetic (pre ganglionic excitatory) nerves the enteric nervous system is able to function with out extrinsic supply

Question 23

Describe the mucous membrane of gut?

Answer 23

Made up of epithelium (varies depending on location and therefore function), lamina propria (connective tissue layer) and muscularis mucosa (thin visceral muscle layer

Question 24

What are the layers of gut wall?

Answer 24

Mucous membrane
Muscle wall (inner circular and outer longitudinal layers)
Adventitia