Anatomy 2 Flashcards
What is a mesentary?
Double folded peritoneum which connect individual viscera to the posterior abdominal wall
What is the mesocolon?
It is a mesentary which connect to a component of the large intestine
What is the role of mesentary?
transmit the neurovascular structures from the posterior abdominal wall where they originate to the intraperitoneal viscera which they supply
Make the intraperitoneal structures more mobile
Why do intraperitoneal structures need to be mobile?
We need these structures to be mobile and flexible, for example the stomach needs to be able to expand to accommodate the influx of food, if it were retroperitoneal it would not be able to expand
Where does the nerve supply of the peritoneum come from?
The structure it lines
What is the implication of the peritoneum receiving a nerve supply from the structures it lines?
Thus there is a somatic nerve supply for the parietal peritoneum and a visceral nerve supply to the visceral peritoneum
Describe the progression of pain in appendicitis with regard to the nerve supply of the peritoneum
The appendix is intraperitoneal, thus
when the appendix becomes inflamed and swells the visceral mesentery around it becomes stretched.
It responds to this but the pain associated with it is dull and poorly localised.
It tends to be referred to the umbilical region.
Eventually the tip of the intraperitoneal appendix will impact on the parietal peritoneum. At this point the person will double over and they will be able to very effectively locate the source of the pain. i.e. the pain is being referred through the somatic nerve supply which is sharp, severe and well localised
Same pattern for pleura and pericardium
Is the peritoneal space real or potential?
The intraperitoneal viscera absolutely fill the abdominal cavity.
Thus the peritoneal space is a potential space only.
What is the role of the serous membrane?
The serous membrane is important for providing a friction free glide with the surrounding viscera especially as parts of the digestive system are peristalsing
What is peritoneal dialysis?
Dialysis fluid is put into the peritoneal space so that the fluid and electrolyte exchange can occur across the vast surface area
What is a potential danger associated with the peritoneal space?
It is a disadvantage if there are tumour seeding into the peritoneal space as it allows the rapid spread of tumour along the smooth serous surface
Where are the kidneys located?
On quadratus lumborum in the paravertibral gutters
Where do the ureters travel?
The ureters travel vertically down psoas and along the tips of the lumbar transverse processes
What can be said about unpaired retroperitoneal viscera?
They are secondarily retroperitoneal
What are the unpaired retroperitoneal viscera?
The duodenum, pancreas, bile duct, ascending and descending colon
What sort of mesentary is present during gut tube development?
Dorsal mesentary
Ventral mesentary
What happens to the ventral mesentary?
This will become the falciform ligament
What does it mean to be secondarily retroperitoneal?
All the structures deriving from the GIT initially possess a mesentery.
During development some of these structures lose their mesentery and become retroperitoneal.
These structures are said to be secondarily retroperitoneal.
Where are structures which are secondarily retroperitoneal located relative to those which are truly retroperitoneal?
§ These will lie in front of the structures which are truly retroperitoneal (the kidney, adrenals and ureter)
What happens to the mesentary of the secondarily retroperitoneal organs?
It is resorbed
Where is the stomach located?
Left upper quadrant
What are the subdivisions of the peritoneal cavity?
The greater sac and the lesser sac
What is contained within the greater sac?
The vast majority of the peritoneal cavity
Where is the lesser sac/omental bursa?
It is a space of the peritoneal cavity which is enclosed behind the stomach
What is the purpose of the lesser sac?
§ This is effectively a bursa behind the stomach so it has a nicer bed to expand and contract against. It is serous filled
What is the communication between the lesser and greater sac called?
The epiploic/omental foramen of winslow
What is twisting of the GIT called?
Torsion
Why is the mesentary divided up?
They provide neurovascular inputs to the gut, thus if one were to twist all of the gut would infarct - thus it is divided up into sections
Why do segments of the gut alternate between itnra and retroperitoneal?
It eliminates the possibility of the whole gut infarcting. The retroperitoneal parts provide strength and stability whilst the intraperitoneal parts are mobile (to better facilitate digestion)
What is the root of ‘The Mesentery’?
Where it leaves the posterior abdominal wall
What is ‘The mesentary’
The root of the mesentery attaching the small intestine is called the mesentery
What is the conformation of ‘The mesentary’?
It extends in an oblique line from the DJ flexure above to the ileo-cecal junction below
Crosses the 3rd part of the duodenum and then the aorta and IVC
And then the right psoas as it heads down to the ileo-caecal junction
What is the transverse mesocolon?
The transverse mesocolon is the double folded peritoneum connecting the transverse colon to the posterior abdominal wall
What is the sigmoid mesocolon?
The sigmoid mesocolon is the double folded peritoneum connecting the sigmoid colon to the posterior abdominal wall
Where is the root of the transverse mesocolon?
Across the front of the pancreas and the second part of the duodenum
Where is the root of the sigmoid mesocolon?
It has a small inverted V shaped attachment to the posterior abdominal wall in the left lower quadrant or left iliac fossa
Where does the lesser omentum attach to the stomach?
The lesser curvature
What is the path of the lesser omentum?
Runs via the liver to the abdominal wall, it then surrounds the liver and then goes up to the diaphragm (also considered to be a wall of the abdominal cavity)
It heads towards the visceral surface of the liver in the region of the porta hepatis
It splits to enclose the liver before heading to the top of the cavity and line under surface of the diaphragm.
At the top of the liver it is the coronary and triangular ligaments
The lesser omentum stops at the point where the duodenum becomes retroperitoneal ◊ This is the free edge of the lesser omentum ◊ Behind the free edge of the lesser omentum one reaches the space behind the stomach - the omental bursa
What is the path of the greater omentum?
Coming off the greater curvature of the stomach
Instead of diving back to the peritoneal wall it creates what is called the fatty apron
It comes off the greater curvature and sweeps all the way down to the suprapubic region and then comes back on itself - it gets impregnated with fat
Why is the greater omentum like 4 layers of peritoneum?
2 layers of greater omentum on its way down and then 2 on its way up towards the posterior abdominal wall
How does the greater omentum get to the abdominal wall - which abdominal wall does it go to?
When it goes back to the posterior wall it goes over the top of, and becomes stuck to, the transverse colon
Thus its attachment to the posterior wall is basically the same as the transverse mesocolon
What are the 2 divisions of the lesser omentum?
Hepatogastric
Hepatoduodenal
Where is the Hepatogastric part of the lesser omentum?
○ The part of the lesser omentum going from the stomach to the liver
Where is the Hepatoduodenal part of the lesser omentum?
The part of the lesser omentum gong from the duodenum to the liver
which parts of the greater curvature give rise to the fatty apron?
It is only the distal part of the first curvature and the first inch of the duodenum
What happens to the section of greater omentum that does not form the fatty apron?
The most superior part goes straight to the diaphragm (i.e. to the left dome)
This is called the gastro-phrenic ligament
The middle part of the stomach makes an impression on the visceral surface of the spleen
The greater omentum splits to enclose the spleen before heading back onto the posterior abdominal wall
Called the gastro-splenic ligament/gastro-lienal ligament
What is the arterial supply to the abdominal aorta, where does it begin?
Abdominal aorta
Begins in the midline at T12/L1
How does the aorta get into the abdomen?
It comes through the aortic hiatus:
Between the crura and behind the diaphragm
Where does the abdominal aorta end?
L4
What does the abdominal aorta become?
Divides into the right and left common iliac arteries
What are the 3 sets of branches coming off the aorta?
3 anterior branches
3 branches off the side
Multiple paired posterior branches
What do the anterior branches of the aorta supply?
Are they paired?
Unpaired
3 anterior branches which supply the GI viscera
What do the side branches of the aorta supply?
Are they paired?
Paired 3 paired branches which supply the paired structures: Adrenals Renals (not ureters) Gonads
What do the posterior branches of the aorta supply?
Are they paired?
Paired
Supply the walls of the abdominal cavity (including the phrenic diaphragm)
What are the 3 unpaired branches off the anterior part of the aorta called?
The celiac trunk
The superior mesenteric artery
The inferior mesenteric artery
What does the celiac trunk do?
It supplies the foregut:
Liver, gallbladder, pancreas and spleen, distal/abdominal oesophagus, stomach and the half of the duodenum (as far as the major duodenal papilla)
What does the Superior mesenteric artery do?
It supplies the midgut:
From the major duodenal papilla, jejunum and ileum, caecum and ascending colon, transverse colon (just proximal to the splenic flexure i.e. it is most of the transverse colon but stops short of the splenic flexure)
What does the Inferior mesenteric artery do?
It supplies the hindgut:
Everything distal to the point proximal to the splenic flexure - last part of the transverse colon, descending colon, sigmoid colon, rectum and first part of the anal canal
Where does teh celiac trunk branch?
It is the first branch off the abdominal aorta
Usually at the superior boarder of the pancreas (T12)
What are the three branches of the celiac trunk?
Left gastric artery
The splenic artery
The common hepatic artery
What direction does the left gastric artery branch off the celiac trunk?
Upwards and to the left
Where does the left gastric artery run?
Heads up to the lesser curvature of the stomach.
It gives oesophageal branches to the abdominal oesophagus.
It then turns and runs along the lesser curvature
What direction does the splenic artery branch off the celiac trunk?
It heads towards the spleen (turns to the left)
Where does the splenic artery run?
It runs along the top of pancreas (the tail of the pancreas is directly related to the hilum of the spleen)
Sometimes it is tucked in behind the superior boarder of the pancreas
It has a very tortuous course - it has lots of little loops and turns
What does the splenic artery supply?
It is the arterial supply to the spleen
It also supplies the major part of the body and tail of the pancreas
It runs behind the stomach
As it does so it sends short gastric arteries to the fundus of the stomach
Also gives off the left gastro-epiploic artery
This runs along the greater curvature of the stomach
What direction does the common hepatic artery artery branch off the celiac trunk?
Turns right to the free edge of the lesser omentum
What does the common hepatic artery give rise to?
Proper hepatic artery
Right and Left hepatic arteries
What course does the proper hepatic artery follow?
Ascends in the free edge of lesser omentum (part of the portal triad)
◊ Portal vein behind, bile duct to the right, artery to the left
What do the right and left hepatic arteries supply?
The two FUNCTIONAL halves of the liver
Where does the cystic artery branch from?
it is variable where it come off, but classically it is a branch of the right hepatic artery
Where does the gastroduodenal artery branch from?
This is a branch off the common hepatic artery
What is the path of the gastroduodenal artery?
Turns down when the proper hepatic artery turns down
It runs behind the first part of the duodenum
It gives off the right gastro-epiploic and the Superior pancreaticoduodenal
Where does the right gastro-epiploic run?
This runs along the greater curvature
Meets and anastomoses with the left gastro-epiploic from the splenic
What does the Superior pancreaticoduodenal supply?
The top half of the duodenum and the head pancreas associated with it
Where does the right gastric branch from?
Comes off the proper hepatic artery as it turns up
Some say it comes off the common hepatic, some say that the proper hepatic can only be considered as such once it has given off the right gastric
Where does the superior mesenteric artery branch?
It comes off the front of the abdominal aorta about 1 cm below the celiac trunk at the level of L1
What is the first branch of the superior mesenteric?
The first branch of the superior mesenteric is the inferior pancreaticoduodenal artery.
Gives this off straight away
What does the inferior pancreaticoduodenial artery supply?
It goes up to meet the superior pancreaticoduodenal artery (which has come down)
Together they supply the C shaped duodenum and the head of the pancreas
What is the route of the superior mesenteric?
Continues along the posterior abdominal wall in the root of the mesentery - it has a diagonal course
From the DJ flexure, across the front of the aorta and IVC, onto right poas, down towards the right lower quadrant
What do all the branches of the superior mesenteric to the left supply?
Every branch to the left goes to the small intestine
A series of jejunal and ileac arteries
These feed into the vascular aracades
What is the arrangement of blood vessels in the mesentary?
Vascular arcade
Vasa recta
What is the difference between the proximal and distal vasa recta/arcades?
In proximal part of the intestine (jejunal region of the mesentery)
Fewer vascular arcades and long vasa recta
In the distal part of the intestine (ileac region of the mesentery)
More vascular arcades and short vasa recta
Where do all right hand branches of the superior mesenteric go?
Every branch to the right goes to the large intestine
What gives off the ileocolic artery?
superior mesenteric
it is the first branch to supply the large intestine
What are the Right and middle colic branches?
Branches of the superior mesenteric which supply the LI.
These are variable They feed into a marginal artery which runs along the edge of the mucosal tube all the way. From this marginal artery (parallel vessel to the mucosal tube) there are short straight arteries heading into the mucosal tube
Where does the inferior mesenteric artery arise?
Arises at the inferior boarder at the 3rd part of the duodenum
Corresponds to L3
What direction does the inferior mesenteric artery head?
It heads diagonally into the left lower quadrant (inferolaterally)
What does the inferior mesenteric artery do?
It gives a series of colic branches.
Terminal portion of the transverse colon, descending colon and sigmoid colon
After it has given off its branches what does the inferior mesenteric become?
It changes its name to the superior rectal artery.
It heads down in the pelvis
What is the venous drainage in the GIT?
Drains through the portal system of veins
Unite to form a single portal vein which unites to bring to blood to the liver via the porta hepatis.
When is the portal vein formed?
The portal vein is created behind the neck of the pancreas at the level of L2.
The portal vein is formed when the splenic vein joins the superior mesenteric vein
What does the portal vein drain?
Gall bladder, tubular GIT, pancreas and spleen
Aside from the liver what are the other tributaries of the IVC?
All the paired structures supplied by the side and back of the abdominal aorta drain into the IVC
All of the structures supplied by the front of the abdominal aorta drain into the portal veins and then into the liver before IVC
Why is cirrhosis a very big problem for the liver?
The portal vein perfuses the liver under relatively low pressure, so if the substance of the liver becomes fibrosed as a result of repeated inflammation or alcohol damage (cirrhosis) then it becomes very hard for the portal vein to push its blood - there is no pressure gradient for portal venous return.
Portal hypertension can then develop
Does the portal system have valves?
No
What happens if the portal vein cannot empty its blood into the liver (due to destruction of the sinusoids)?
Reverse flow may occur
What happens to blood flow when there is portal hypertension?
The alternative way of getting the blood into the IVC occur at points where there is an overlap between venous drainage into the portal system and venous drainage into the systemic system
These are called sites of porto-systemic anastomosis
How many sites of porto-systemic anastomosis are there?
5
What are the sites of porto-systemic anastomosis?
Lower end of the oesophagus
The anal canal
The anterior abdominal wall
Retroperitoneal space behind the ascending and descending colon
The top of the liver where it sits against the diaphragm
Why is the lower oesophagus a site of porto-systemic anastomosis?
Middle 3rd is drained by veins that empty into the azygous
Lower 3rd is drained by oesophageal veins that try to get into the portal system
If they cannot drain the veins become very enlarged and eventually push the blood through the azygous tributaries and into the IVC, but they get so dilated and engorged with blood in the submucosa part of the oesophagus that they can often rupture with for eg a sharp piece of food or vomiting etc ◊ This causes massive hematemesis ◊ People may arrive at casualty with a bucket of vomited blood from the oesophageal varices
Why is the anal canal a site of porto-systemic anastomosis?
Where the superior rectal vein goes into the portal system
It will become engorged and try to push its blood through the middle and inferior rectal veins which drain into the systemic system
People using these porto-systemic anastomoses as shunts get very large haemorrhoids (dilated veins in the anal region)
Why is the anterior abdominal wall a site of porto-systemic anastomosis?
Their veins drain into the IVC, but the umbilical vein (which is ligamentum teres) can open up push blood out to the anterior abdominal wall
Why is the Retroperitoneal space behind the ascending and descending colon a site of porto-systemic anastomosis?
□ Behind the retroperitoneal viscera the venous tributaries can anastomose directly with the veins of the posterior abdominal wall
What innervates the abdominal viscera?
The ANS
Where are preganglionic sympathetic fibres of the derived from?
T6-L2
Where are the sympathic ganglion clusters?
Around unpaired branches of the aorta and renal arteries
Where is parasympathetic innervation from in the forgut and midgut?
The vegus
Where is parasympathetic innervation from in the hindgut?
splanchnics
How do the postganglionic fibres pas to viscera?
With blood vessels
Where doe the ganglionic fibres for the foregut come from
T6-9
Where doe the ganglionic fibres for the midgut come from
T8-12
Where doe the ganglionic fibres for the hindgut come from
T12-L2
Where do the visceral afferent pass?
Visceral afferents pass to same spinal cord segment involved in sympathetic innervation up to mid sigmoid colon.
But beyond that they run with parasympathetics
What does the fact that visceral afferents pass to same spinal cord segment involved in sympathetic innervation up to mid sigmoid colon mean for referred pain in that area?
Afferent fibres carrying pain from all unpaired abdominal viscera proximal to the mid-sigmoid will refer pain to midline of anterior abdominal wall (dermatomes T6-L2)
What does the fact that visceral afferents beyond the sigmoid colon run with parasympathetics mean in terms of referred pain?
Afferent fibres from the mid-sigmoid down will refer pain to perineal region (dermatomes S2-4)
