Overview
The aorta leaves the left ventricle and carries oxygenated blood to the whole body; the caudal vena cava returns blood from the abdomen, pelvis and pelvic limbs to the right atrium. Both run close to the vertebral column, but they part company at the level of the liver and heart.
Aorta
- Aortic arch: curves dorsally and caudally from the heart base. In ruminants it gives off a single branch, the brachiocephalic trunk, which supplies both subclavian arteries and the bicarotid trunk.
- Thoracic aorta: runs through the mediastinum, ventral to the thoracic vertebrae and slightly to the left, and gives off the intercostal arteries. It enters the abdomen through the aortic hiatus of the diaphragm.
- Abdominal aorta: ventral to the lumbar vertebrae; it gives off the coeliac artery (for the stomach, liver and spleen), the cranial and caudal mesenteric, renal and gonadal arteries. It ends at the pelvic inlet by dividing into the external and internal iliac arteries.
- Uterine artery: in the cow it arises from the umbilical artery, a branch of the internal iliac, and runs in the broad ligament.
Caudal vena cava
It forms at the pelvic inlet from the union of the common iliac veins and runs along the roof of the abdomen to the right of the aorta. Cranially it moves away from the spine and becomes embedded in the dorsal border of the liver, where it receives the hepatic veins. It crosses the diaphragm through the caval foramen and, in the thorax, runs in the fold of the vena cava, accompanied by the right phrenic nerve, to the right atrium.
Clinical relevance
- Caudal vena cava thrombosis: a liver abscess, often secondary to ruminal acidosis, erodes the vein and forms a septic thrombus. Emboli reach the lung and cause abscesses, arteritis and aneurysms of the pulmonary arteries; their rupture causes haemoptysis, epistaxis and sometimes sudden death.
- Rectal palpation: the aorta and its terminal branches are felt against the roof of the pelvis. In advanced pregnancy the uterine artery of the pregnant horn enlarges and transmits a palpable fremitus, a sign used in pregnancy diagnosis.
- Neck vessels: the external jugular vein, in the jugular groove, is, with the coccygeal vein, one of the usual blood sampling sites in cattle, and the usual route for intravenous injection.