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The Embryological Organization of the Gut Tube:
- subdivided into 3 parts defined on the basis of their blood supply:
- The foregut structures are supplied by celiac arterial trunk system.
- The midgut structures are supplied by the superior mesenteric artery system.
- The hindgut is supplied by the inferior mesenteric artery system.
- supplied by celiac arterial trunk system
- Foregut structures include: the stomach, proximal 1/2 of the duodenum, pancreas, liver, gallbladder, (the spleen is associated with foregut structures but does not develop embryologically from the primitive foregut).
- Innervated by �the celiac plexus.�
- Forgut sturcture lies below the left dome of the diaphragm and is that part of the gut tube between the esophagus and duodenum.
- The greater omentum attaches to its greater curvature.
- The lesser omentum attaches from its lesser curvature to the liver.
- You should be familiar with the following parts of the stomach: the fundus, body, pylorus (leading into the duodenum), lesser & greater curvatures.
blood supply to the stomach
- left gastric a. (a direct branch of the celiac trunk),
- right gastric a. (a branch of the proper hepatic a.),
- which anastomose along the lesser curvature,
- left gastroepiploic a. (br. of the splenic a.) and
- right gastroepiploic a. (br. of the gastroduodenal a.) which anastomose along the greater curvature.
The Celiac Arterial Trunk
- main blood supply to the foregut structures.
- main branches are:
- common hepatic artery,
- left gastric artery (to the lesser curvature of the stomach on the left side)
- splenic artery (passing posterior to the stomach)
Celiac Arterial Trunk & Branching Pattern
- Common hepatic artery
- proper hepatic artery (one of the portal triad structures)
- right gastric artery (to lesser curvature of stomach)
- right & left hepatic arteries (to the liver)
- gastroduodenal artery (passes posterior to duodenum)
- right gastroepiploic artery (to greater curvature of stomach)
- superior (ant. & post.) pancreaticoduodenal a. (head of pancreas)
- Left gastric artery (to lesser curvature of stomach)
- Splenic artery (to body of pancreas and spleen)
- short gastric arteries (to stomach)
- left gastroepiploic artery (to greater curvature of stomach)
Portal Triad (Porta Hepatis) Structures
- consist of three anatomical structures that course in the free edge of the lesser omentum (hepatoduodenal ligament portion) which forms the anterior wall of the epiploic foramen (entrance into the lesser sac).
- common bile duct (to the right)
- proper hepatic artery (to the left)
- portal vein (posterior to the other two).
Gall Bladder & Bile Ducts
- The gall bladder stores excess bile and is located on the visceral surface of the liver.
- The gall bladder is supplied by the cystic artery which is usually a branch of the right hepatic artery.
- (note: the right and left hepatic arteries are branches of the proper hepatic artery).
extends from the gall bladder and joins the common hepatic duct to form the common bile duct.
common hepatic duct
formed by right and left hepatic ducts extending from the liver.
Duodenum (proximal �)
- first part of the small intestine
- has a C-shape in which the head of the pancreas sits.
- The main pancreatic duct and common bile duct come together to form a short wide ampulla as they drain into the duodenum.
- A spinchter controls the discharge of bile and pancreatic secretions into the duodenum.
- The duodenum is derived from both foregut and midgut, so it receives its blood supply from both the celiac trunk and superior mesenteric a.
- an endocrine & exocrine organ.
- It secretes pancreatic enzymes into the duodenum and releases hormones (glucagon & insulin) into the blood stream.
- It has a head, neck, body, and tail.
- It is supplied mostly by branches of the celiac arterial trunk (e.g., the splenic a. & superior pancreaticoduodenal as.) but also receives some branches of the superior mesenteric a. (e.g., the inferior pancreaticoduodenal as.)
- largest organ in the body.
- many metabolic functions also stores glycogen and secretes bile which passes to the gall bladder via hepatic and cystic ducts.
- It is attaches to the anterior body wall by the falciform ligament (which contains the round ligament in its base).
- It is attached to the diaphragm by the coronary ligament and to the stomach by the lesser omentum.
- These three ligaments are the mesenteries of the liver and are embryologically derived from the primitive ventral mesentery.
- The liver has 4 morphological lobes: right, left, quadrate, and caudate lobes.
- (note: the round ligament and the ligamentum venosum represent an obliterated duct system which shunted blood away from the liver and into the IVC in the fetus)
Liver Blood supply
- double blood supply.
- It receives oxygenated blood (30% of the total blood received) from the
- right & left hepatic arteries (which are branches of the proper hepatic artery which is a branch of the common hepatic artery which is one of the three main branches of the celiac trunk).
- It receives deoxygenated blood (70% of the total blood received) from the GI tract via the portal vein.
- The portal vein usually receives blood from the superior mesenteric, splenic, and inferior mesenteric veins.
- The blood from the liver then drains into right and left hepatic veins which drain into the IVC.
portal venous system
- The portal vein is an example of a portal venous system.
- A portal venous system is formed when blood drains from one capillary bed (e.g., the gut tube) into veins and then into another capillary bed (e.g., in the liver).
- the distal � of the duodenum, the remainder of the small intestine (i.e., the jejunum, the ileum), cecum, ascending colon, and transverse colon of the large intestine.
- supplied by branches of the superior mesenteric arterial (SMA) trunk.
- innervated by an autonomic nerve plexus which surrounds this trunk and its branches (the superior mesenteric plexus).
The Jejunum & Ileum
- The jejunum constitutes the proximal 2/5th s (9 ft) and the ileum, the distal 3/5th s (14 ft).
- Both are attached to the posterior wall of the peritoneal cavity by a mesentery called �The Mesentery.�
- Travelling in the Mesentery are 15-18 intestinal branches of the superior mesenteric a. which supply the jejunum and ileum.
- The jejunum is larger in diameter, more vascular, and has a greater internal surface area (via prominent plica circularis � circular infolding of the mucosa) than the ileum.
- the ileum joins the large intestine at the iliocecal junction.
- The cecum is a large blind-sac like structure at the beginning of the large intestine.
- Projecting inferiorly from the cecum is the vermiform appendix.
- The appendix has its own mesentery called �the mesoappendix.�
- Superiorly, the cecum is continuous with the ascending colon.
- The iliocecal junction and ascending colon are supplied by the iliocolic br. of the superior mesenteric a. The ascending colon is retroperitoneal.
- the ascending colon bends as it approaches the liver.
- The bending is called �the hepatic or right colic flexure.�
- This flexure is supplied by the right colic br. of the SMA.
- The transverse colon courses horizontally to the left toward the spleen.
- The transverse colon has its own mesentery called �the transverse mesocolon.�
- It is supplied by the middle colic br. of the SMA.
- descending colon, the sigmoid colon, and the rectum.
- These structures are supplied by branches of the inferior mesenteric a. (IMA).
- The inferior mesenteric nerve plexus follows the course of the arterial branches to reach the hindgut structures.
- as the transverse colon reaches the spleen, it bends and forms the splenic or left colic flexure as it becomes the descending colon.
- The left colic flexure is supplied by the left colic br. of the IMA.
- The descending colon is retroperitoneal.
The Sigmoid Colon
- inferiorly the descending colon is continous with the sigmoid colon which courses over the pelvic brim and thus has an �S� or �sigmoid� shape.
- The sigmoid colon has its own mesentery called �the sigmoid mesocolon.�
- It is supplied by sigmoidal branches of the IMA.
- as the sigmoid colon courses over the pelvic brim, it dives inferior to the peritoneum of the floor of the peritoneal cavity.
- As it does so, it becomes the rectum which is retroperitoneal.
- The inferior mesenteric artery follows it and as it dives below the peritoneum, it changes names to become the superior rectal a.
large intestine 3 characteristics
- in addition to its larger diameter, that distinguish it from the small intestine.
- These are the appendices epiploica (or omental appendices), tenia coli (3 bands of longitudinally arranged muscles), and haustra (a series of pouches or pockets).
Blood Supply to the Gut
- from 3 unpaired arterial trunks orginating off the abdominal aorta:
- the celiac trunk (supplying foregut structures),
- the superior mesenteric artery (supplying midgut structures)
- the inferior mesenteric a. (supplying hindgut structures)
The Celiac Trunk
- has 3 main branches: the left gastric a., the splenic a., and the common hepatic.
- The left gastric a. is related to the lesser curvature of the stomach.
- The splenic artery courses posterior to the pancreas and heads toward and supplies the spleen.
- It supplies the pancreas as well as giving off the left gastroepiploic a. which courses along the greater curvature of the stomach.
- The common hepatic a. gives off the gastroduodenal and then changes names to become the proper hepatic a (which is one of the porta hepatis structures).
- The proper hepatic a. gives off the right gastric a. which courses along the lesser curvature of the stomach (to anastomose with the left gastric a.)..
- The proper hepatic then continues on toward the liver and divides into right and left hepatic arteries (which supply the liver).
The Superior Mesenteric Artery
- has 15-18 intestinal branches that supply the jejunum & ileum,
- the iliocolic artery which supplies the iliocecal region and ascending colon,
- the right colic artery which supplies the right colic flexure,
- and the middle colic artery which supplies the transverse colon.
The Inferior Mesenteric Artery
- has the left colic artery which supplies the left colic flexure,
- the sigmoidal arteries which supply the sigmoid colon, and
- ends as the superior rectal artery which supplies the rectum.
Autonomic Innervation to the Gut
- the structures of the foregut, midgut, and hindgut are supplied by autonomic plexuses that follow the arterial trunks and their branches that supply each region.
- The plexuses are named after the arterial trunks.
- celiac plexus which follows the branches of the celiac trunk,
- superior mesenteric plexus that follows all the branches of the SMA,
- inferior mesenteric plexus that follows the branches of the IMA.
- These plexuses have the same functional components as those visceral nerve plexuses of the thorax (VA, VE-symp/post, VE para/pre).
Gut Sympathetic fibers
- In general, the preganglionic (symp/pre) fibers of the greater, lesser, and least thoracic nerves from the thorax pierce the diaphragm and synapse on special pre-aortic ganglia (celiac, superior mesenteric, inferior mesenteric and aortico-renal ganglia) that are located near each of the three arterial trunks.
- From these ganglia, symp/post fibers join one of the 3 nerve plexuses (celiac, superior mesenteric, or inferior mesenteric plexus).
Gut Para/pre fibers
- in the celiac plexus (to foregut structures) and superior mesenteric plexus (to midgut structures) come from the vagus nerve (these para/pre cell bodies are in the brainstem).
- Para/pre fibers in the inferior mesenteric plexus come from the sacral region of the spinal cord (S2-4 spinal cord segments via the pelvic splanchnic nerves.
- These para/pre cell bodies are in the lateral gray horn of the S2-4 spinal cord segments