Abdominal Anatomy (Chapter 5)- Omentum and arterial Supply of the Abdomen

Question 1

Where is the transpyloric plane? and what Organs does it transect

Answer 1

bisects the body midway between the jugular notch and pubic symphysis
o Cuts the costal margins at tip of 9th costal cartilage, which is at the lateral border of the rectus abdominus (semilunar line)
o Beneath on the left is the fundus of the gall bladder and on the right the body of the stomach
o Passes through the 1st lumbar vertebrae  conus medularis and the pylorus of the stomach
o Also passes through the head of the pancreas behing the pylorus of the somach as well as the neck and body, just above the attachment of the transverse mesocolon
o SMA leaves the aorta at this plane and splenic vein behind the pancreas
o Hilum of each kidney is in this plane
o Above lies the liver, spleen and fundus of the stomach (supracolic compartment) and below lies the small intestine and stomach (infracolic compartment)

Question 2

What are the peritoneal folds of the anterior abdominal wall

Answer 2

• Above 1) The falciform ligament: contains the ligamentum teres at its base (obliterated remains of the umbilical vein) and left umbilical vein –> round ligament of the liver and tehir associated paraumbilcal veins. Passes upwards from the midline and deviates rightwards and enters its named fissure on the liver on its visceral surface and continues upwards on the anterior and superior surface of the liver before separating
• Below: 1) Median umbilical fold. Contains the median umbilical ligaments (remains of the urachus)
o 2+3) medial umbilical fold. Contains medial umbilical ligaments (obliterated remains of umbilical artery) – one on each side
o Above three inserts at umbilicus
o 4+5) lateral umbilical fold. Contains inferior epigastric vessels which enter the rectus sheath passing beneath the arcuate line

Question 3

What is the lesser sac and what is its boundaries?

Answer 3

boundaries of the lesser sac
Lesser sac (Omental bursa): space behind the stomach, created by the peritoneum of liver, stomach and spleen
o Opens to the greater sac by the epiploic foramen, in front of the IVC
o Anterior wall: stomach and lesser omentum and gastrocolic omentum
 Left it extends to the hilum of the spleen – to form the lienorenal ligament and the gastrosplenic
o Roof: sloping roof of peritoneum that covers the caudate lobe of the liver
o Inferior wall wall is transverse mesocolon, attached to the lowest part of the pancreas
 Incision of either of the above leads to greater ability to explore the lesser sac due to the space bound posteriorly by the pancreatico gastric and duodenal folds
• Posterior wall is parietal peritoneum

Question 4

Where is the greater omentum attached?

Answer 4

• greater curvature of the stomach - continuous from abdominal oesophagus to duodenum - the 4 layers fuse and hang off the greater curvature
• connects the stomach to the spleen by the gastrosplenic ligament and spleen and kidney via the lienorenal ligament
• Above the spleen the greater omentum passes from the back of the stomach to the diaphragm above the kidney as the gastrophrenic ligament
• The greater omentum immediately below the stomach fuses with the transverse mesocolon – forming the gastrocolic omentum

Question 5

What are the compartments of the peritoneum?

Answer 5

• Due to the attachment of the peritoneum to the posterior abdominal wall – the cavity is divided into 3 compartments
o 1) supra colic 4x subdivisions
 Right upper and lower, left upper and lower
o 2) infracolic – 2x subdivisions
 Right (upper), left (lower)
o 3) pelvic

Question 6

What divides the supracolic and infracolic compartments of the peritoneum? And where does this attach?

Answer 6

The transverse mesocolon attachment at the posterior abdominal wall.

Attachment of the transverse mesocolon as follows: lower border of the pancreas, extends over the top of the duodenum to the right kidney at the hepatic colic flexure, leftwards it extends to the splenic flexure attaching to the lower half of the left kidney

Question 7

How is the supracolic compartment further subdivided?

Answer 7

• Divisions of supracolic compartment defined by attachments of the liver to the diaphragm and abdominal wall
o To the right of the falciform ligament, over the top of the liver, the space is bound by the upper layer of the coronary ligament – this space is the right sub phrenic compartment
o Still to the right of the falciform, underneath the liver and above the kidney the space is bound posteriorly by the lower layer of the coronary ligament- this is the right subhepatic comparotment, also known as the hepatorenal pouch (of Morrison) - fluid accumulates here when lying flat
o The left subdiaphragmatic compartment: left of the falciform ligament and bound posteriorly by the left triangular ligament posteriorly
o The left subhepatic compartment is the lesser sac

Question 8

How is the infracolic compartment divided?

Answer 8

• into upper and lower divisions by the root of the mesentery
• The root of the mesentery path as follows: begins at the left at the duodenojejunal junction, crossing over the third part of the duodenum, where the superior mesenteric vessels enter, continuing downwards over the top of the aorta and IVC, right psoas muscle and ureter to the right iliac fossa

Question 9

What is the structure and contents of the upper infracolic compartment?

Answer 9

• triangular shape- base is the transverse mesocolon, sides are the ascendign colon and attachment of the mesentery
• at its apex lies the ileocolic junction
• at the floor- lower pole of the kidney and ascending branch of the right colic vessles. The duodenum - descending part and transverse part also lie beneath
• of note one must transverse over ileum to reach the pelvis

Question 10

The boundaries and components of the floor of the lower infracolic compartment?

Answer 10

Quadrilateral shape= four sides
o Upper Border: transverse mesocolon attachment, from the duodenojejunal flexure on the left of the midline and the splenic flexure further leftwards
o Right border—attachment of the mesentry
o Left border: paracolic gutter lies to the left of the descending bowel
- inferior boder- sigmoid mesocolon

Contents of the floor:
The ascending part of the duodenum lies in the upper angle
 The para duodenal fossa lies to the left of the ascending duodenum and contains the inferior mesenteric vein
o Floor of this compartment is shallowest in the midline due to the lumbar vertebrae and aorta and IVC protruding in
o The left paracolic gutter lies to the left of the descending colon – it is limited superiorly by the phrenicolic ligament – a fold of peritoneum between the splenic flexure and the diaphragm (fluid such as infection cannot spread above this)
 The gutter leads into the pelvis to the left of the sigmoid mesocolon attachment

Question 11

What organs lie in the retroperitoneal space?

Answer 11

Aorta 
IVC 
Cisterna Chyli 
Lymph nodes 
nerves (lumbar plexus) and sympathetic trunk 
kidney 
ureters
pancreas 
duodenum
suprarenal glands

Question 12

What are the foetal mesentery and their associated blood supply?

Answer 12

• By the 6th week of life the alimentary canal is a tube - and is fixed in the midline posteriorly by the dorsal mesentery
• 3 arteries supply the gut and subdivisions of the dorsal mesentery. they are:
• – the coealiac artery to the dorsal mesogastrium which suspends the foregut
• – the SMA to the dorsal mentery which suspends the midgut
• – the IMA which supplies the dorsal mesocolon and suspends the hindgut

The foregut has an additional mesentery - the ventral mesentery -which attaches it to the anterior abdominal wall - into which the liver and part of the pancreas develops
- • The pancreas develops as two outgrowths- one in the dorsal mesogastrium and one on the ventral mesogastrium  these fuse and exchange ducts systems  but structurally this creates the main and accessory pancreatic ducts

the arterial supply remains constant for the derivatives of the fore, id and hind gut
- exception is the spleen which is not technically part of teh foregut but formed by the growth of cells that mirgate into the left leaf of the dorsal mesogastrium

Question 13

What is the general structure of lymphnode drainage of the GIT?

Answer 13

Mucous membranes –>lymphoid follicles in gut submucosa –> lymphnodes are located at the margin of the gut and the mesentry (the epi group – eg epicolic)–> further nodes in the mesentry before the root of the artery there are the para group (eg paracolic) –> preaortic nodes (coeliac, superior and inferior mesenteric

Question 14

What are the key embryological processes in the development of the abdominal cavity discussed by Lasts?

Answer 14

1) herniation of the gut
2) rotation of the midgut
3) movement of the hind gut
4) Growth of the liver
5) rotation of the foregut

Question 15

What occurs during the herniation of the midgut?

Answer 15

• growth of the liver and gut by the end of the 6th week of life means the abdomen is to small for its contents
• a phsyiological hernia - where a loop of the gut protrudes into the umbilical cord
• this apex of this loop is at the attachment of the vitellointestinal duct (the site of meckels diverticulum) and is where the SMA main branch is directed
• for the SMA - there are many proximal branches of arteries to the Meckel’s diverticulum, which supply- jejunum and ileum, however tehre are only 3 branches distal to its apex- the ileocolic, right colic and middle colic arteries
• by the 10th week the abdominal cavity has grown enough to accommodate gut and the hernia reduces

Question 16

What occurs during Rotation of the midgut and subsequent development?

Answer 16

• As the loop of midgut returns to the abdomen - it rotates so that the distal limb - goes upwards and to the left and the proximal limb goes down and to the right- ie a 270 degree anticlockwise rotation
• rotation occurs around the SMA- so that proxmal branches of the loop come to lie on the left (ileal and jejunal) and the distal lie on the right (ileocolic, right and middle colic)
• Proximal loop mesentary fusion: once back in the abdomen the duodenal part of the midgut (distal to bile duct) becomes plastered to the posterior abdominal wall as rotation has caused its peritoneum to come into contact with the posterior abdominal wall, with transverse mesocolon over the top
• migration of caecum: the caecum lies in the midline and higher up - it then grown down and to the right - taking distal ileum with it to lie in the RIF
• Distal loop mesentery movement and fusion: the distal dorsal mesentary swings to the right- like a door on a hinge- where its 2 layers contact the parietal peritoneum of the Right colic gutter - the left layer fuses and the right layer remains forming teh floor of the right infracolic compartment, with the colic vessels lying immediately deep to it
• the most distal part of teh dorsal mesntary remains and does not fuse- as teh transverse mesocolon

Question 17

What occurs during Movement of the hind gut

Answer 17

• As the midgut loop returns to the abdominal cavity, the hindgut swings on its dorsal mesocolon, like a door across to the left
o This causes the two layers of peritoneum to come into contact with the left paravertebral gutter (3 layers)
• The two deeper layers of peritoneum fuse and are absorbed, and the anterior layer remains as the floor of the left infracolic compartment
o The left colic vessels lie immediately beneath this as the most anterior structure of the posterior abdominal wall ay this part
• Fusion of dorsal mesocolon is incomplete in beneath the pelvic brim  giving rise to the sigmoid mesocolon

Question 18

what occurs during the Growth of the liver

Answer 18

• the liver develops from the hepatic bud in distal forgut, growth separates the ventral mesogastrium into falciform ligament and lesser omentum
• caudally - the liver pushes down the free edge of the ventral mesogastrium until the umbilical vein (ligamentum teres) notches its inferior border and is enclosed in a deep groove on its under surface

•As the liver grows cranially towards the diaphragm is peels apart the left and right leaves of the ventral mesogastrium
o The left leaf of the mesogastroium sweeps up and to the left and folds back on itself to, creating a double fold and becoming the left triangular ligament
o The right leaf – sweeps to the right and folds back on itself, although the folds are not close together, this creates the upper layer of the coronary ligament, the right triangular ligament and the lower layer of the coronary ligament
 The space between the two folds of the right leaf is the bare area of the liver
 The lower layer of the coronary ligament reflects onto the kidney creating the hepato-renal pouch

Question 19

What are the hepatic attachments of the lesser omentum

Answer 19

• The attachment of the lesser omentum runs behind the behind the fissure for the ligamentum teres (a fissure that lodges the fibrous remnant of the ductus venosum (ligamnetum venosum) on the underside of the liver
• The attachment of the lesser omentum passes to the left of the IVC to the diaphragm, causing to be attached between the diaphragm and the end of the oesophagus

Question 20

What occurs during rotation of the foregut

Answer 20

• liver swings to the right as it grows and the stomach to the left
• In doing so the stomach elongates and develops a convex dorsal border and concave venral border - the stomach
• the distal foregut (duodenum) does not dilate, instead its mesentary shortens, grows into a loop and swings to the right - and is plastered to the posterior abdominal wall.
• — Its walls also grow assymetrically - moving the bile duct entry to the medial side
• fixation at oesophagus and duodenum -allows for axis of rotation- 90 degree to the left- so that the dorsal covex border faces left (greater curvature) and the ventral concave border facces right (lesser curvature)

Question 21

what are the other changes during the rotation of the forgut (3 things)

Answer 21

• the dorsal mesogastrium is initially attached in the midline - swinging takes it to the left
• the left layer comes in contact with the posterior abdominal wall as far left as the kidney and fuses before being resorbed - this leaves the right layer which becomes the posterior abdominal wall
• with fusion the left gastric and splenic branches of the coeliac come to lie behind immediately deep to the posterior abdominal wall

o From in front of the left kidney and diaphragm above the 2 layers of the dorsal mesograstium pass to oesophagus and greater curvature of the stomach to form the greater omentum
 This is the left boundary of the lesser sack
 The spleen develops from the left left leaf into the greater sac and divides this part of the omentum into the gastrosplenic and lienorenal ligaments

o The more caudal part of the dorsal mesogastrium – it attached to the greater curvature of the stomach and 1st inch of the duodenum- its dorsal attachment hinges to the left and becomes attached to the peritoneum of the posterior abdominal wall and fused over the top of the pancreas
 Below this from the greater curvature it balloons down like and apron over transverse mesocolon, before returning to the abdominal wall – with 2 layers of double mesogastrium
 The deeper part of the mesogastrium fuses with the transverse mesocolon and and transverse colon forming the lower limit of the lesser sac, the rest of the mesogastrium fuses and hangs down as the greater omentum

Question 22

What are the 3 branches of the coeliac trunk?

Answer 22

The coeliac trunk comes off just after the aorta passes through the diaphragm at T12
division occurs at upper border of pancreas into:
1) left gastric - runs on left crus of diphragm to oesophagus
2) Splenic - tortuous- behind pancreas, left crus and psoas and to the hilum of the kidney - before turning forward into the leiorenal ligament
3) common hepatic - runs down over the superior border of the pancrease, continuing, to the 1ts part of teh duodenum - where it turns superiorly to enter the 2 layers of lesser omentum - continues as hepatic

Question 23

What is the branches and path of the left gastric artery?

Answer 23

 The left gastric artery runs upwards across the left crus towards the oesophagus
o It gives off an oesophageal branch
o It then enters the lesser omentum and runs along the lesser curvature – rightwards to anastomose with the right gastric artery

Question 24

What is the branches of the splenic artery and their respective paths?

Answer 24

o Before breaking into the splenic branches it gives off
 Short gastic arteries which run in the gastrosplenic ligmanet to the stomach fundus
 Left gastroepiploic artery which curves down and runs along the greater curvature in the greater omentum and joins its right gastroepiploic artery

Question 25

Branches and path of the common hepatic artery

Answer 25

 The common hepatic – passes over the upper border of the pancreas, continuing downwards and to the right behind to peritoneum of the lesser sac to the first part of duodenum. It then turns forwards at the epiploic foramen and curves upwards into the space between the two layers of the lesser omentum – continuing as the hepatic artery
o On the left of the hepatic artery is the bile duct and both lie in front of the portal vein
 On reaching the portahpeatidis – the hepatic artery divides into right and left branches –> subsequent accessory hepatic arteries
o The common hepatic also gives off the right gastric artery – normally branches off as it turns into the lesser omentum–> meets the left on the lesser curvature
o Also gives of the gastroduodenal artery which passes behind the first part of the duodenum to the left of the portal vein before dividing into two- divisions as follows
 The right gastroepiploic – passes forward between the first part of the duodenum and the pancreas and turns left to enter the greater omentum at the front of the head of the pancreas  travels along greater curvature to join its left counterpart
 The superior pancreaticoduodenal divides into a smaller anterior and larger posterior branch to encircle the head of the pancreas and concavity of the duodenum down to the entrance of the bile duct
• Anastomoses with the inferior pancreaticoduodenal arteries
 Of note the bile duct marks the end of the foregut and start of the midgut – hence artery supply meet here

Question 26

What is the path of the SMA?

Answer 26

• Super mesenteric artery: arises from the 1cm below the coealic trunk at the level of L1, it is directed downwards behind the splenic vein and the neck of the pancreas
o The superior mesenteric vein lies to its right, both travel down and over the uncinate head of the pancreas and the third part of the duodenum
o Lies on the left renal vien
o The vessels then enter the upper end of the mesentrym and then pass along the root of the mesentry, then directing itself ot the place of meckels diverticulum
o Pressure from the superior mesenteric artery may produce a left sided varicocele and chronic duodenal ileus

Question 27

Venous supply of the foregut

Answer 27

• superior mesenteric continues as the portal vein after it receives the splenic vein behind the neck of the pancreas – all stomach veins drain into this
• the oesophageal veins drain into the left gastric vein in the lower 1/3
• left gastric follows artery and drain into the the portal at vein
• right gastric - empties into portal vein
• – receives prepyloric vein
• The short gastric and left gastroepiploic runt through the gastrosplenic ligament and greater omentum to the spleen hilum  drain into the splenic vein
• The splenic veinbegins at the hilum of the spleen, it passes with the tail of the pancrease below the splenic artery, through the lienorenal ligament to lie over the hilum of the left kidney, before straightening to run behind the pancreas

The right gastroepiploic - runs with artery to exiting the greater omentum at its attachment over the head of the pancreas and runs over the front of the pancreas to join the superior mesenteric vein at the lower border of the neck of the pancreas
• Super pancreatico- duodenal veins: runs behind the curve of the duodenum and head of the pancreas to join the portal vein

Question 28

What are the branches of the SMA?

Answer 28

•The inferior pancreaticoduodenal: first branch, arising from the posterior surface. Runs in the curve between duodenum and pancrease, and anastomoses with the superior pancreaticoduodenal

• ileal and jejunal branches
• ileocolic
• right colic
• middle colic

Question 29

what are the branches and path of the ileocolic artery

Answer 29

• Ileocolic artery: arises from the right of the SMA trunk at base of mesentry, where it travels towards the ielocaecal jnunction where it gives off ileal branch which anastomoses with the terminal branch of thre SMA and a colic branch which travels left and up along the ascending colon, behind the peritoneum to anastamose with the right colic artery
o The colic branch also gives off the anterior and posterior caecal arteries

Question 30

what are the branches and path of the right colic artery?

Answer 30

• The right colic artery: branches from the right side of the SMA trunk, often in common with the ileocolic artery. It traves behind the peritoneum over the right psoas, gonadal vessels, ureter, genitofemoral nerve and quadratus lumborum. It didvides at the left side of the ascending bowel into ascending and descending branches
o The ascending branch runs up over the inferior pole of the right kidney to the heapatic flexure where it anastomoses with the middle colic
o Descending anastomoses with ileocolic colic branch

Question 31

What are the branches of the Middle colic artery?

Answer 31

• The middle colic artery: is the highest up of the branches of the SMA. Emerges at the lower border of the neck of the pancreaand passes forwards into the transverse mesocolon. It runs downwards (although illustrations portray upwards as the transverse colon is lifted)
o Lies to the right of the midline and divides into left and right branches at the colic border
o Right anastomoses with roght colic
o Left – supplies nearly to splenic flexure and anastomoses with the left colic artery
o As it lies to the right of the midline there is an avascular window in the left of the transverse mesocolon for surgical access to the lesser sac and posterior stomach wall

Question 32

Describe the venous drainage of the midgut?

Answer 32

• All artery branches are accompanied by a vein which drains into the Superior mesenteric vein
• The superior mesenteric vein lies to the right of the artery, it crosses the third part of the duodenum and runs between the uncinate process and the neck of the pancreas, where it is jojned by the splenic vein to form the portal vein
o The SMV is continuous with the portal vein, and becomes the portal vein after the splenic vein joins

Question 33

describe the path of the IMA

Answer 33

• Supplied by the inferior mesenteric: arises off the front of the aorta at the inferior border of the duodenum, at L3 (also the level of umbilicus)
o It runs obliquely beneath the floor of the left infracolic compartment to the pelvic brim, where it crosses at the bifurcation of the left common iliac vessels at the sacroiliac join, it then converges in the ureter (although it does not cross) at the apex of the V attachment of the sigmoid mesocolon. It then continues along the pelvic wall in the root of the sigmoid mesocolon as the superior rectal artery
 In it course is lies on the aorta, left psoas, left sympathetic trunk, left common iliac and hypogastric nerve

Question 34

what are the branches of the IMA?

Answer 34

Left colic artery, 3-4x sigmoid arteries and superior rectal

Question 35

What are the branches of the left colic artery?

Answer 35

• The left colic artery: leaves the trunk and travels leftwards towards the splenic flexure, beneath the left infracolic compartment peritoneal floor
o It branches after a short course to the ascending and descending branch
 The ascending travels laterally and upwards over the left psoas muscle, ureter and genitofemoral nerve and quadratus lumborum. It is crossed by the inferior mesenteric vein
• The ascending divides into a upper branch- which passes across the left kidney inferior pole to the splenic flexure
o And a lower branch – which passes transversely to the descending colon
• Each upper and lower branch divides which anastomose with the left branch of the middle colic artery and with each other to continue the arterial circle of the large intestine
 The descending branches passes laterally but downwards crossing the same structures as the ascending branch but lower dwon and divides above the pelvic brim to 2-3 branches
• They pass to the left behind the peritoneum of the iliac fossa and supply the lower part of the descending colon and the sigmoid colon forming anastomosing loops before doing so

Question 36

venous supply of the hindgut

Answer 36

superior rectal vein runs in the root of the sigmoid mesocolon left of the superior rectal artery–> at the pelvic brim it becomes inferior mesenteric vein –> receives tributaries the same as the arteries

Question 37

Path of the inferior mesenteric vein

Answer 37

• runs on the left of the IMA, under the infracolic compartment
• runs over the left psoas muscle and vessels, ureter and genitofemoral nerve
• just below the attachment of the transverse mesocolon lies to the left of the duodenojejunal flexure, where it raises a ridge, forming the paraduodenal recess
• it the curves to the right and passes below the border of the pancreas body, in front of the left renal vein to join the splenic vein