Like many parts of the body, the digestive system and circulatory system are related in a number of integral ways. When most people think of the circulatory system, they picture the heart and lungs acting to pump blood throughout the body. Only few understand the enteric requirement of the circulatory system. The enteric system, or the gut, which contains many digestive organs, requires about 30% of all cardiac output. This large amount of blood, needed for ongoing digestive functions, is the basis for the interrelation of the two systems.
Understanding the complex dynamics among bodily systems requires a basic understanding of each system independently. Generally speaking, the digestive system breaks down food that is consumed. This system acts to divide the food into necessary components, like vitamins and nutrients, and allows for absorption of these nutrients into the bloodstream. The circulatory system acts to move these necessary nutrients around the body as well as transport unwanted materials away.
Although the relationship between the digestive system and circulatory system is extensive, there are two primary ways in which these systems rely on each other. The first is the need of the circulatory system for digestion to continue to function. The second is the delivery of nutrients from the digestive system to the body's bloodstream for circulation.
Like all organs and systems of the body, blood is constantly needed for performance. The blood itself is not crucial, but the nutrients within this vital fluid are. These nutrients supply the tissues and cells with chemicals they need to continue living. The bottom line is that, without nutrients, there is no life, and without circulation, there are no nutrients.
Although the digestive system needs blood from the circulatory system to work properly, the circulatory system also needs the digestive system. As food breaks down, it moves from the esophagus to the stomach and into the intestines. Eventually, the broken-down foodstuffs reach the vascular small intestines, where absorption occurs. It is in this region where many vital substances move from the food in the intestines into the circulatory system.
Digestion is almost constantly occurring, so in part due to the absorptive properties of the intestines, there remains a high demand for blood flow to the enteric region. This is the physiological reason behind the high percentage of flow to this area. There may be more links between the two systems but, in simple terms, this is how they interact.