Anatomy: Blood Supply to the Abdomen

Symptoms of AAA (Not Ruptured)

-75% are asymptomatic and usually found incidentally -May be a palpable pulsatile mass on exam in epigastric or umbilical region

Portal Circulation

-A blood flow pattern of the arteries→to capillaries→to veins→to capillaries to veins -Additional set of veins and capillaries interposed within the typical systemic circulatory pattern -Additional set of capillaries allows additional processes before the blood is returned to the heart

Colic Branches of the Superior Mesenteric Artery (SMA)

-Arise from the concave side (right) of the SMA -Middle colic artery→projects to transverse colon -Right colic artery→projects to ascending colon -Ileocolic artery→projects toward the ileocecal junction -Near the junction arise branches to distal ileum, cecum, appendix, and end proximal ascending colon -Terminal ileal branches anastomose with distal end of SMA

Diagnosis of Ruptured AAA

-Bedside ultrasound -There could be free fluid in potential abdominal spaces, such as Morison's pouch and subphrenic spaces

Sinusoids of the Liver

-Capillaries of the liver fed by the portal vein -Coalesce into the hepatic vein that exit the liver and unite with the IVC

Venous Tributaries of the Portal Vein

-Carry deoxygenated blood from the capillaries of the GI tract -Capillary beds extend from the lower esophagus to upper rectum -Venous return of pancreas, gallbladder and spleen

Single Midline Branches of the Abdominal Aorta

-Celiac trunk -Superior mesenteric artery -Inferior mesenteric artery -Median sacral artery (small vessel that arises from the midline near aortic bifurcation and then descends into pelvic cavity)

Celiac Trunk Branches

-Common hepatic artery -Splenic artery -Left gastric artery

Marginal Artery of Superior Mesenteric Artery (SMA)

-Continuous arterial channel formed by anastomoses between various colic branhces of the superior and inferior mesenteric arteries -Parallels the inner margin of the colon

Blood Draining into the IVC

-Directly receives the paired branched veins -Single branch veins have a venous first pass through hepatic portal circulation and then enter the IVC via hepatic veins

Celiac Artery (Trunk)

-First single midline branch the abdominal aorta -Originates just below the diaphragm near T12 -"Trunk" because it is a short, stubby vessel

Formation of the Common Iliac Veins

-Formed by the union of the external and internal iliac veins along the pelvic brim -Carry the venous return of much of the lower limb and pelvis

Paired Branches of the Abdominal Aorta

-Inferior phrenic arteries (arise near aortic hiatus and ascend under diaphragm to which they supply blood) -Middle adrenal arteries (project laterally to adrenal glands) -Renal arteries -Lumbar arteries (four pairs of arteries that project laterally to abdominal wall) -Ovarian and testicular arteries (descend to supply gonads)

Branches of the -Superior Mesenteric Artery (SMA)

-Intestinal branches -Colic branches -Marginal artery

Divisions of the Common Iliac Arteries

-Left and right external iliac arteries→descend into anterior thighs where they are renamed the left and right femoral arteries -Left and right internal iliac arteries→descend over pelvic brim into the pelvic cavity where they supply blood to pelvis

Branches of the Inferior Mesenteric Artery (IMA)

-Left colic artery→projects to the descending colon -2-4 sigmoid arteries→supply sigmoid colon *Both the left colic and sigmoid arteries contribute to the marginal artery

Inferior Vena Cava (IVC)

-Originates at L5 by the union of the left and right common iliac veins -Ascends the posterior abdominal wall immediately to the right of the abdominal aorta -Traverses the central tendon of the diaphragm at the caval opening -Quickly unites with the RA upon entering thorax

Incidence of AAA

-Present in 5% of US population -Incidence is increasing (reflecting increase in age of population) -15th leading cause of death in US

Superior Rectal Vein

-Renamed the inferior mesenteric vein when it ascends out of the pelvis and into the abdomen -It then ascends on the left side of the posterior abdominal wall to its union behind the body of the pancreas with the splenic vein

Location of Abdominal Aorta

-Retroperitoneally on anterior surface the bodies of the lumbar vertebrae -Terminates at L4 by dividing into left and right common iliac arteries

Superior Mesenteric Artery (SMA)

-Second single midline branch in abdominal aorta -Originates just below celiac trunk at L1 -Enters the mesentery of the small intestine, passing between two layers of peritoneum among the adipose tissue

Shape of Superior Mesenteric Artery (SMA)

-Shaped like an archer's bow -Convex side to the left -Concave side to the right

Left and Right Common Iliac Arteries

-Terminal branches of the abdominal aorta -Arise at L4 -Course inferolaterally just above the plevic brim where they divide

Inferior Mesenteric Artery (IMA)

-Third single midline branch of the abdominal aorta -Originates near L3 (4cm above the bifurcation of the abdominal aorta) -Courses retroperitoneally on the left side of the posterior abdominal wall until it enters the sigmoid mesocolon -Descends over pelvic brim into pelvis where it is renamed the superior rectal artery

Intestinal Branches of the Superior Mesenteric Artery (SMA)

-Usually 12-20 branches from the convex (left) side of the SMA -Course toward the jejunum and ileum -Form anastomosing arcades which arise from vasa recta that project to and pierce the intestinal wall

Abdominal Aorta

Direct continuation of the descending thoracic aorta (renamed when it passes through the hiatus of the diaphragm)

Risk of Rupture of AAA

Large risk when AAA has reached 5 cm, though some can reach 15 cm

Abdominal Aortic Aneurysm (AAA)

Permanent, localized dilation of the wall of the abdominal aorta

Formation of the Portal Vein

Superior mesenteric vein and the splenic vein unite behind the neck of the pancreas