L9. Nerves and Vessels of the Abdomen

Question 1

Where does anterior supply of the blood to the abdomen come from? Describe the path of this vessel

Answer 1

Abdominal aorta

It begins at the midline at T12/L1 (where it crosses the diaphragm) and ends anterior to L4 by dividing into a right and left common ileac artery (external for lower limb and internal for pelvis)

Question 2

Describe the major classes of branches coming off the abdominal aorta (3) and generally what they supply

Answer 2

There are three unpaired sets of branches as it descends: supply gastrointestinal viscera and the derivatives [shown in green]

Three paired branches coming of the lateral edges of the abdominal aorta for the paired structures: kidneys, adrenals, and the gonads (ovaries and testes - because they develop in the lumbar region and descend)

A series of paired posterior branches which supply the walls of the abdominal cavity (diaphragm and lumbar vessels: phrenic and lumbar)

Question 3

What are the three major layers of the primitive gut tube

Answer 3

Foregut, Midgut and Proximal gut

Question 4

What are the three unpaired anterior branches off the abdominal aorta that supply the abdominal contents?

Answer 4

1. Celiac trunk
2. Superior Mesenteric Artery: SMA and
3. Inferior Mesenteric Artery: IMA

Question 5

What is the relationship between the three abdominal layers of the primitive gut tube and the unpaired anterior branches

Answer 5

Celiac trunk supplies the foregut
Superior mesenteric artery supplies the midgut
Inferior mesentery artery supplies the proximal gut tube

Question 6

What does the foregut tube give rise to?

Answer 6

Makes up the solid viscera from the gut tube: liver, gall bladder, pancreas, spleen, plus the first part of the GIT abdominal oesphagus, stomach and duodenum down to the major duodenal papilla

Question 7

What does the midgut tube give rise to?

Answer 7

Rest of duodenum, Jejunum and ilium, cecum and ascending colon, transverse colon (just proximal to the splenic flexure

Question 8

What does the proximal gut tube rise to?

Answer 8

Everything beyond that point (rest of transverse colon) of the splenic flexure, descending, sigmoid, rectum and first part of the anal canal

Question 9

What is the first branch off the front of the aorta? Describe it and where it comes off

Answer 9

Celiac Trunk is the first branch off the front of the aorta. It is short wide trunk before breaks down into terminal branches. Usually arises at the superior border of the pancreas (T12) and immediately breaks into 3 branches

Question 10

What are the three branches of the celiac trunk?

Answer 10

Left gastric Artery
Splenic Artery
Common Hepatic Artery

Question 11

Describe the course of the left gastric artery and what it supplies

Answer 11

It arches upwards and to the left to lesser curvature of the stomach giving supply into the stomach. It gives oesophageal branches and then turns and runs along the lesser curvature

Question 12

Describe the course of the splenic artery and what it supplies

Answer 12

It runs along the superior border of the pancreas towards the hilum of the spleen (very torturous course with lots of twists & turns). It also supplies the major part of the body and tail of the pancreas as it runs with it. As it also runs behind the stomach it sends short gastric vessels to the fundus of the stomach and gives the LEFT GASTRO-EPIPLOIC ARTERY which runs along the greater curvature of the stomach.

Question 13

Describe the course of the common hepatic artery and what it supplies

Answer 13

It turns right to the free edge of the lesser omentum where gives rise to PROPER HEPATIC ARTERY which ascends in the free edge of the omentum to the porta hepatis.

Typically the CYSTIC ARTERY branches off the right hepatic artery (but variability in where it arises occurs) to supply the gall bladder.

It also gives off a branch called the GASTRODUODENAL ARTERY, which turns down and runs behind the first part of the duodenum. It gives rise to the right gastroepiploic running along the greater curvature and meets the left gastroepiploic from the spleen.

The gastroduodenal artery also gives off the SUPERIOR PANCREATICODUODENAL ARTERY (top half of duodenum and head of pancreas associated with it). The RIGHT GASTRIC ARTERY comes off the proper hepatic artery as it has already turned up in the free edge of the lesser omentum.

Question 14

When and how does the Superior Mesenteric Artery Arise?

Answer 14

Comes of front of the abdominal aortic artery under the celiac trunk about the level of L1
The artery that supplies the midgut structures

Question 15

What is the first branch of the SMA? What is its course and what does it supply?

Answer 15

The INFERIOR PANCREATICODUODENAL ARTERY, which is given off straight away and goes up to supply the inferior part of the head of the pancreas and distal part of the duodenum

Question 16

How does the superior mesenteric artery descend down the abdominal cavity? What is important to know as it does this?

Answer 16

The SMA ‘walks’ along posterior abdominal wall in the oblique root of The mesentery from DJF, crossing front of vessels, psoas major muscle towards the right lower quadrant.

As it descends.. brancesh on the left = small intestine and branches on the right = large intestine

Question 17

Describe the arterial supply to the small vs. large intestine via the superior mesenteric artery

Answer 17

LEFT: Jejunal and iliac arteries which feed into vascular arcades and then to vasa recta

RIGHT: Colic arteries (that are variable) off the right side of the superior mesenteric artery: ILIOCOLIC ARTERY, right and middle COLIC BRANCHES supplying parts of the midgut colons.

Question 18

Describe the colic and marginal artery organisation of supply to the intestine

Answer 18

COLIC ARTERIES (superior or inferior) feed into MARGINAL ARTERIES which run along the edge of the mucosal tube of the large intestines all the way around (parallel vessel) and intermittently giving off short, straight arteries into the mucosal tube.

Question 19

Where and when does the inferior mesenteric artery arise from the abdominal aorta?

Answer 19

At the inferior border of the third part of the duodenum (At the level of L3)

Question 20

Describe the path of the inferior mesenteric artery

Answer 20

Heads diagonally into the left lower quadrant, inferior laterally and gives off a series of colic branches:
These supply the terminal transverse colon, descending and sigmoid colon

After this it changes its name into the SUPERIOR RECTAL ARTERY and heads down into the pelvis

Question 21

Where do all gastrointestinal tract and derivative organs drain their venous blood into? What is the exception?

Answer 21

All through the portal system of veins

All except the liver

Question 22

Describe the venous drainage of the gastrointestinal contents

Answer 22

Venous systems of the various parts of the tube and the derivative organs (except liver) unite into a single PORTAL VEIN, which takes the portal blood to the liver via the porta hepatis.

Question 23

Why does venous drainage from the gut go through the liver?

What happens to the blood after it has passed through the liver?

Answer 23

At the porta hepatis it splits into left and right and into the liver to into the lobes of the liver through hepatic sinusoids for cleansing of the blood it collects

After, the blood recollects into hepatic veins and into the IVC just before it passes through the diaphragmatic hiatus.

Question 24

Where do the retroperitoneal structures: adrenal, renal, gonadic, phrenic and lumbar veins drain into?

Answer 24

Directly into the IVC

Question 25

How does portal hypertension arise?

Answer 25

Portal vein perfuses liver at a relatively low pressure. If liver sinusoids becomes fibrosed (Eg. repeated inflammation, cirrhosis - alcohol damage) there is no pressure gradient for portal flow: difficult venous return into liver.

Question 26

What is a major characteristic of the portal veins that allows for a compensatory mechanism for portal hypertension?

Answer 26

The portal venous system is valveless, it allows a reversal of flow and portal venous system looks for an alternative way of getting blood into the IVC.

Question 27

What kind of sites does the venous blood tend to shunt into the systemic blood?

Answer 27

This occurs at sites where there is an overlap of venous drainage into the portal system and into systemic system = porto-systemic anastomosis (tributaries portal vein is next to tributaries vein of IVC)

Question 28

What are the 5 major or alternative routes for deoxygenated blood to leave the gastrointestinal area?

Answer 28

• Lower end of the oesophagus (because the middle oesophagus goes into azygous)
• The anal canal: because the middle and inferior veins drain into the IVC thus when the superior rectal vein gets engorged blood is forced here
• The veins of the anterior abdominal wall (the umbilical vein, now ligamental teres - in desperate times can open and recanalise allowing blood flow through veins in the anterior abdominal wall)
• Enteric: When abdominal blood meant for the portal system sits in the abdomen: retroperitoneal space behind ascending/descending colon and another top of the liver where it sits against the diaphragm

Question 29

What branch of the nervous system is the abdominal viscera innervated by?

Answer 29

Autonomic

Question 30

Describe the sympathetic and parasympathetic innervation of the abdominal viscera

Answer 30

• Sympathetic ganglion cluster around the unpaired branches of aorta and the renal arteries. The Preganglionic sympathetic fibres are derived from T6-L2
• The Parasympathetic innervation is from VAGUS to foregut and midgut but PELVIC SPLANCHNICS for hindgut

Question 31

How do the sympathetic post-ganglionic fibres pass from the sympathetic ganglia to their respective viscera?

From where to the nerves arise for the three different segments?

Answer 31

Postganglionic fibres pass to viscera with blood vessels in the mesentery:

• foregut T6-9
• midgut T8-12
• hindgut T12-L2

Question 32

Describe the visceral AFFERENTS

Answer 32

Visceral afferents pass to same spinal cord segment involved in
sympathetic innervation up for all segments and organs up to the mid sigmoid colon.

Beyond that they run with parasympathetics

Question 33

Describe the signalling of pain of the abdominal viscera (through which regions does the pain refer to?)

Answer 33

Afferent fibres carrying pain from all unpaired abdominal viscera proximal to mid-sigmoid will refer pain to midline of anterior abdominal wall (dermatomes T6- L2) but afferent fibres carrying pain from mid-sigmoid down will refer pain to perineal region (dermatomes S2-4).