27.6: Blood Supply to the Digestive System

Splanchnic circulation refers to the network of blood vessels that supply and drain blood from the abdominal organs involved in digestion, including the stomach, liver, pancreas, intestines, and spleen. This circulation delivers essential nutrients and oxygen while removing waste products from these organs.

Blood Supply to the Digestive System: The splanchnic circulation involves three main arteries: the celiac artery (also known as the celiac trunk) and the superior and inferior mesenteric arteries. These arteries arise from the abdominal aorta and branch out to supply specific regions of the digestive system.

Celiac Artery: The celiac artery is the first major branch of the abdominal aorta. It divides into three main branches, namely the left gastric artery, splenic artery, and common hepatic artery.

1. Left Gastric Artery: This artery supplies blood to the lesser curvature of the stomach and connects with the right gastric artery.
2. Splenic Artery: The splenic artery branches into multiple smaller vessels, providing blood to the spleen and pancreatic branches.
3. Common Hepatic Artery: The common hepatic artery further divides into the proper hepatic artery, which supplies blood to the liver, and the gastroduodenal artery, which provides blood to the stomach and the first part of the duodenum.

Superior Mesenteric Artery: The superior mesenteric artery arises from the abdominal aorta just below the celiac artery. It is responsible for supplying blood to the small intestine, cecum, ascending colon, and part of the transverse colon.

Inferior Mesenteric Artery: The inferior mesenteric artery arises from the anterior aspect of the abdominal aorta at the level of the third lumbar vertebra and supplies blood to the distal large intestine.

The branches of the superior mesenteric artery form an extensive network within the small intestine, ensuring optimal nutrient absorption and oxygen delivery for digestion.

Venous Drainage: After the organs receive oxygen and nutrients through the arterial supply, the blood is drained by the hepatic portal system. This system collects blood from the splanchnic veins and transports it to the liver, where it undergoes filtration and detoxification before returning to the heart via the inferior vena cava.

The blood vessels serving the digestive system have two functions. They transport the protein and carbohydrate nutrients absorbed by mucosal cells after food is digested in the lumen. Lipids are absorbed via lacteals, tiny structures of the lymphatic system. The blood vessels' second function is to supply the organs of the GI tract with the nutrients and oxygen needed to drive their cellular processes.

Specifically, the more proximal parts of the alimentary canal are supplied with blood by arteries branching off the aortic arch and thoracic aorta. Below this point, the alimentary canal is supplied with blood by arteries branching from the abdominal aorta. The celiac trunk services the liver, stomach, and duodenum, whereas the superior and inferior mesenteric arteries supply blood to the remaining small and large intestines.

The veins that collect nutrient-rich blood from the small intestine (where most absorption occurs) empty into the hepatic portal system. This venous network takes the blood into the liver, where the nutrients are either processed or stored for later use. Only then does the blood drained from the alimentary canal viscera circulate back to the heart. To appreciate just how demanding the digestive process is on the cardiovascular system, consider that while you are "resting and digesting," about one-fourth of the blood pumped with each heartbeat enters arteries serving the intestines.

Blood supply to the digestive system is facilitated through the splanchnic circulation.

The celiac trunk and the mesenteric arteries provide oxygenated blood to the gastrointestinal tract organs. 

The celiac trunk branches into — the left gastric, splenic, and common hepatic arteries, supplying the esophagus, stomach, liver, duodenum, and pancreas.

The superior mesenteric artery supplies the small intestine, parts of the large intestine, and the pancreas, while the inferior mesenteric artery serves the distal large intestine.

The superior mesenteric vein drains blood from the small intestine and part of the large intestine.

The splenic and inferior mesenteric veins drain blood from the fundus, areas of the stomach, pancreas, and distal large intestine.

The right gastric vein drains blood from parts of the esophagus, duodenum, and areas of the stomach, while the left gastric vein drains blood from the esophagus, stomach, and pancreas.

The hepatic veins drain blood from the liver and empty it into the inferior vena cava.