Duodenum, Pancreas, and Abdominal Aorta LO4
4. Describe the branches of the abdominal aorta and the inferior vena cava.
The thoracic aorta become the abdominal aorta at the aortic hiatus (of the diaphragm), approximately at the T12 vertebral level. The abdominal aorta descends anterior to the bodies of the vertebrae, sending branches to viscera and the body wall along its length, until bifurcating (approximately at L4) into the common iliac aa.
The branches of the abdominal aorta may be conceptualized as: 1) anteriorly oriented, unpaired branches to viscera, 2) laterally oriented, paired branches to viscera, and 3) posterolaterally oriented, paired branches to the body wall.
Anteriorly oriented, unpaired brs. to viscera:
- Celiac (~T12)
- Superior mesenteric (~L1)
- Inferior mesenteric (~L3)
Laterally oriented, paired brs. to viscera:
- Suprarenal (~L1)
- Renal (~L1)
- Gonadal (~L2)
Posterolaterally oriented, paired brs. to body wall:
- Inferior phrenic (~T12)
- Subcostal (~T12)
- Lumbar aa (~L1-L4)
The inferior vena cava (IVC) is the major vein which returns blood from the back, abdominal wall, pelvis, and abdominopelvic viscera. The IVC begins at the union of the common iliac veins (~L5), is transmitted through the caval opening of the diaphragm (~T8), and ends in the right atrium of the heart. The IVC is also: found to the right of the abdominal aorta, is valveless, and typically has tributaries that mirror the branches of the abdominal aorta. Some exceptions of venous return mirroring abdominal aortic brs. exist, e.g. the hepatic portal system, hepatic vv., and the unique tributaries of the left renal v. (L. inferior phrenic v., L. suprarenal v., & L. gonadal v.).
All blood returning through the SVC and IVC is part of the caval system. Blood returning from the abdominopelvic GI viscera is part of the hepatic portal system. This blood is delivered to the liver via the hepatic portal v., is processed in the liver, and returns to the caval system via a variable number of hepatic vv. (typically 3).