Blood vessels of abdomen & pelvis
The abdomen and pelvis receive their arterial supply principally from the abdominal aorta and its branches. The abdominal aorta is the largest vessel in the abdominal cavity. It begins at the level of the twelfth thoracic vertebra (T12), from the aortic hiatus present in the diaphragm. It descends in front of the vertebral bodies, to the left of the inferior vena cava. It terminates at the level of the fourth lumbar vertebra (L4) by bifurcating into right and left common iliac arteries to supply the lower portion of the body. The abdominal aorta has both parietal and visceral branches.
Branches of the Abdominal Aorta
The abdominal aorta gives off the inferior phrenic arteries, a pair of parietal arteries originating posteriorly at the level of the twelfth thoracic vertebra (T12). These arteries supply the diaphragm. At the level of the first lumbar vertebra (L1), the celiac, superior mesenteric and middle suprarenal branches of the abdominal aorta arise. The celiac artery or trunk is a large unpaired visceral artery that supplies the liver, the stomach, the abdominal esophagus, the spleen, the superior duodenum, and the superior pancreas. The superior mesenteric artery is an unpaired visceral artery as well. It supplies the distal portion of the duodenum, the jejuno-ileum, the ascending colon, and part of the transverse colon. The middle suprarenal arteries are small paired visceral arteries that supply the adrenal glands. Between the first and second lumbar vertebrae (L1-L2), the renal arteries originate to supply the kidneys. The gonadal arteries, or the testicular arteries in males and ovarian arteries in females, are a pair of visceral arteries that arise laterally at the level of the second lumbar vertebra (L2). At the level of third lumbar vertebra (L3), the unpaired inferior mesenteric visceral artery arises anteriorly to supply the large intestine from the splenic flexure to the upper part of the rectum. The median sacral artery is an unpaired parietal artery that originates posteriorly at the level of the fourth lumbar vertebra (L4) to give arterial supply to the coccyx, lumbar vertebrae and the sacrum. In addition to all of these arteries, four pairs of parietal lumbar arteries arise posterolaterally to supply the abdominal wall and the spinal cord.
Veins of the abdomen and pelvis return deoxygenated blood to the heart via the inferior vena cava. The inferior vena cava is formed by the joining of the two common iliac veins at the level of the fifth lumbar vertebra (L5). It ascends to the right of the aorta, passes through the central tendon of the diaphragm at the level of the eighth thoracic vertebra (T8), and empties into the right atrium of the heart. Its tributaries include the common iliac, gonadal, renal, suprarenal, inferior phrenic, lumbar, and hepatic veins.
The common iliac veins are formed by the joining of the external and internal iliac veins. These veins drain the lower limbs, and the pelvic and gluteal regions. The gonadal veins are the right testicular or ovarian vein. They drain the right testis or ovary respectively in men and woman. The left testis or ovary is drained by the left renal vein. The renal veins also drain the kidneys and left adrenal gland, while the right suprarenal vein receives the venous blood from the right adrenal gland. The inferior phrenic veins drain the diaphragm. The lumbar veins on the other hand, drain the posterior wall of the abdomen. And the liver is drained by the hepatic veins.
Structures like the spleen, pancreas, gallbladder, and the abdominal part of the gastrointestinal tract are drained by the portal venous system. The portal vein transports venous blood to the sinusoids of the liver to be processed, from there, the blood is carried by the hepatic veins to the inferior vena cava.