Abdominal Vasculature

Summary of GI Tract Below the Diaphragm Blood Supply

- Celiac Trunk & Branches --> supply upper 1/3 - Superior Mesenteric Artery & Branches --> supply middle 1/3 - Inferior Mesenteric Artery & Branches --> supply lower 1/3

Additional Rectal Arteries

- Middle Rectal Arteries --> arise from the internal iliac arteries - Inferior Rectal Arteries --> arise from the internal pudendal arteries

The hepatic portal system also has other tributaries...

a. The left and right gastric veins drain directly into the portal vein. b. The cystic vein drains the gallbladder either in the liver or the portal vein directly.

There are three unpaired arterial branches of the abdominal aorta...

1) Celiac Artery 2) Superior Mesenteric Artery 3) Inferior Mesenteric Artery Associated with the 3 arterial branches are sympathetic ganglia that bear the same names, i.e. the celiac ganglion, the superior mesenteric ganglion, and the inferior mesenteric ganglion. Note also the left and right aorticorenal ganglia as they overlie the origin of the left and right renal arteries, respectively, as they split off the abdominal aorta.

Tributaries of the portal vein

1. The *splenic vein*: leaves the spleen through the hilum and lies above the pancreas, but below the splenic artery. The tributaries of the splenic vein are the *short gastric*, the *left gastroepiploic*, the *inferior mesenteric*, and the *pancreatic veins*. 2. The *inferior mesenteric vein*: joins usually the splenic vein (sometimes the superior mesenteric vein), receives the superior rectal veins, the sigmoid (rectosigmoid) and the left colic veins. 3. The *superior mesenteric vein*: joins the splenic and receives the jejunal, ileal, ileocolic, right colic, middle colic, pancreaticoduodenal and right gastroepiploic veins.

The two terminal branches of the abdominal aorta are:

1. The common iliac arteries, which in turn split into the external and internal iliac arteries. 2. The middle or median sacral artery, which is unpaired and appears as a direct continuation of the aorta. It gives off the 5th lumbar arteries.

Two groups of non-visceral paired branches of the abdominal aorta that supply the musculature of the abdominal cavity:

1. inferior phrenic arteries: supply the diaphragm and give off the superior suprarenal arteries to the adrenal glands. 2. lumbar arteries: 4 pairs to the posterior abdominal musculature. The 5th lumbosacral arteries arises from the middle sacral artery.

Three paired visceral branches of the abdominal aorta:

1. middle suprarenal arteries: for the adrenal gland. 2. renal arteries: for the kidneys, which gives off an inferior suprarenal artery to the adrenal gland. 3. gonadal arteries: for the gonads (testicular or ovarian).

Inferior mesenteric artery

Inferior mesenteric artery supplies blood to the lower GI tract, i.e. left portion of the transverse colon, descending colon, sigmoid colon and rectum. {emerges from the abdominal aorta above its branching into the common iliac arteries} There are 3 main branches of the inferior mesenteric artery: *left colic* (distal 1/2 of transverse colon and entire descending colon), *sigmoid* (sigmoid colon), and *superior rectal arteries* (superior rectum).

Celiac Artery

Provides blood to the upper GI tract below the diaphragm, i.e. stomach, spleen, gall bladder, pancreas, duodenum , and esophagus and liver. The celiac artery has 3 main branches, which are: - the *left gastric artery* (runs along the lesser curvature of the stomach and gives off an esophageal branch) - the *splenic artery* (runs along the superior portion of the body and tail of the pancreas to the spleen and gives off: 1) the left gastroepiploic artery, 2) short gastric arteries, 3) the dorsal pancreatic artery, and, 4) the greater pancreatic artery; - the *common hepatic artery*, which splits into: 1) the hepatic proper artery (with right/left hepatic branches and the cystic arterial branch from the right hepatic artery. The hepatic proper artery also gives off the right gastric artery.), 2) the gastroduodenal artery, which gives off the supraduodenal artery and the right gastroepiploic artery. The two gastric arteries noted above supply and form an anastomosis along the lesser curvature of the stomach, whereas the two gastroepiploic arteries supply and form an anastomosis along the greater curvature of the stomach. Note also that the right gastro-epiploic artery gives off the anterior and posterior superior pancreaticoduodenal arteries, which form an anastomosis with the anterior and posterior inferior pancreaticoduodenal arteries around the head of the pancreas.

Superior mesenteric artery

Superior mesenteric artery supplies blood to the mid GI tract, i.e. duodenum, pancreas, jejunum, ileum, cecum, appendix, ascending colon, and right portion of the transverse colon. (hooks over the left renal vein) There are 5 main branches of the superior mesenteric artery: *jejunal, inferior pancreaticoduodenal, middle colic* (1/2 transverse colon), *right colic* (ascending colon), and *ileocolic arteries* (ileocecal junction). Notice how the arteries form arterial arcades within the mesentery, which then form vasa recta as the intestinal wall is approached. (creates a circular blood flow)

Formation of the HPS

The HPS is formed by the junction of the splenic vein and superior mesenteric vein. These two structures accompany their respective arteries and join to form the hepatic portal vein behind the neck of the pancreas. The hepatic portal vein then ascends to the right, behind the duodenum to enter the lesser omentum and finally the porta hepatis (a fissure on the liver's surface between the caudate and quadrate lobes), where it divides into a right and left branch of the portal vein.

The common iliac arteries

The abdominal aorta terminates at L4 where it branches into common iliacs, at about the level of umbilicus. The right and left common iliac arteries are the terminal branches of the aorta. After branching off the aorta, the two arteries run downward and laterally along the medial border of the psoas muscle. The common iliac arteries end at the level of the sacroiliac joint by dividing into the external and internal iliac arteries. Note that the ureters, from the kidneys, cross the common iliac arteries at that level. Note also the intermesenteric plexus and the superior and inferior hypogastric plexi, (joined by the right and left hypogastric nerves) which follow along the aorta and its large branches. These plexi supply autonomic innervation to the abdominal and pelvic viscera.

The hepatic portal system (HPS)

The hepatic portal vein is the terminal portion of the HPS, and drains the gastrointestinal tract from the lower third of the esophagus to the upper part of the anal canal, including the blood from the spleen, pancreas and gallbladder. The portal vein carries the blood to the liver where it is filtered in the sinusoids and then back into the vena cava through the hepatic veins. The hepatic portal system gets the molecular material from the gut to the liver.

The Inferior Vena Cava (IVC)

The inferior vena cava is formed by the union of the common iliac veins at L4 (umbilicus) and courses up the posterior abdomen to the right of the vertebral column. The IVC passes through the posterior substance of the liver between the caudate and right lobes, and then passes through the diaphragm via the caval hiatus. Draining into the IVC from the liver are the right, left, and middle hepatic veins. Note also the right/left renal veins, which drain into the IVC. The right gonadal vein drains into the IVC; however, the left gonadal vein drains into the left renal vein.

The portal-systemic anastomoses

The portal venous blood normally flows, via the hepatic circulation, into the inferior vena cava. However, four other small communications exist between the portal and the systemic systems allowing passage of venous blood to the systemic circulation if the portal becomes obliterated: 1. The esophageal branches of the left gastric vein anastomose with the esophageal veins from the middle third of the esophagus into the azygos vein 2. The superior rectal veins from the upper anal canal anastomose with the middle and inferior rectal veins 3. The para-umbilical veins from the left branch of the portal vein anastomose with the superficial veins of the anterior wall 4. The veins from the ascending colon and descending colon anastomose with the veins of the posterior wall (i.e. the lumbar veins).

Aorta and its Branches

The thoracic aorta becomes the abdominal aorta when it passes through diaphragm at T12, the aortic hiatus. The aorta then descends anterior to vertebral bodies of the lumbar vertebrae. The left sympathetic trunk runs parallel (but unattached) to the aorta, on the left side. Note that the aorta is positioned slightly to the left of the midline, with the inferior vena cava on the right side. The right sympathetic trunk can be observed on the right of the inferior vena cava.

Sympathetic Prevertebral Ganglia

These Ganglia are associated with the abdominal arteries by the same name: - *Celiac Ganglion* --> override the celiac trunk - *Superior Mesenteric Ganglion* --> lies above the superior mesenteric artery - *Inferior Mesenteric Ganglion* --> lies above the inferior mesenteric artery - *Left/Right Aorticorenal Ganglion* --> where renal arteries come off of aorta Significance: - pre-vertebral ganglia; receive sympathetic pre-ganglionic from the *Splanchnic Nerve* - bypass the sympathetic chain ;slows everything down [decrease secretions & peristalsis]