Figure 3-8
Major arteries and veins of the digestive system in the abdominal cavity.

The abdominal viscera are supplied with arterial blood by three unpaired arteries and one paired set of arteries. All arise directly from the abdominal aorta: (Figure 3-8)

• Celiac Trunk
• Superior Mesenteric
• Inferior Mesenteric
• Paired Renal Arteries

The celiac trunk lies immediately inferior to the diaphragm and is the most superior of the three unpaired arteries. It quickly branches into a large splenic, a common hepatic and a small left gastric artery. The celiac trunk serves the stomach, pancreas, spleen, liver, gallbladder and parts of the duodenum.

The superior mesenteric artery rises from the descending aorta slightly inferior to the celiac trunk. It supplies the duodenum, jejunum, ileum, cecum, ascending colon and approximately half of the transverse colon. It reaches these organs through the mesentery.

The inferior mesenteric artery arises from the inferior end of the descending aorta, just slightly superior to the aortic bifurcation. This small artery supplies the rest of the transverse colon, the descending colon, the sigmoid colon and the rectum.

The paired renal arteries emerge from the aorta at about the same level as the superior mesenteric artery, and are posterior to, and hidden by, the large renal veins.

Paired gonadal arteries and paired lumbar arteries come off the abdominal aorta between the origins of superior and inferior mesenteric arteries.

Venous drainage of the digestive system is unique. Most venous blood from the organs of the G.I. system drains into the hepatic portal vein to end in the sinusoids of the liver. These sinusoids can be considerd venous capillary networks. In them, surrounded by liver cells, the liver does its "thing". These venous sinusoid channels then join each other to form the hepatic vein to empty into the inferior vena cava.

Figure 3-9
Major veins of the hepatic portal system.

Venous blood from the digestive organs flows to the liver via the separate hepatic portal venous system. Liver actions are carried out before the blood returns to the general venous circulation via the inferior vena cava. (Figure 3-9)

The portal venous system does, however, connect with the caval system in several portal-caval venous anastomosis. Normally, little venous blood is exchanged between these two blood systems. However, if an obstruction exists in the portal system (cirrhosis of the liver resulting in hepatic hypertension), then venous blood in the portal system can flow in the reverse direction. Remember the veins of the gut have no one-way valves like the veins of the extremities. The blood will then find its path to the caval system by way of these venous to venous anastomoses.