Which shows the best connection between the digestive and excretory systems

The digestive system and excretory system are two bodily systems with seemingly unrelated functions: that of breaking down food for energy and that of removing waste from the body, respectively. There is, however, a good deal of overlap in the relationship between the digestive system and excretory system. In particular, the liver plays a role that relates to both systems, as it receives blood from the intestines and filters out post-digestive waste such as drugs and alcohol before that blood is cycled back into the body. It then releases bile, a substance that is necessary to the filtering process, back into the intestines in exchange. That bile then becomes a part of the stool that is eliminated from the body during defecation.

The digestive system includes all organs and passageways of the digestive tract, including the mouth, throat, esophagus, stomach, liver, gallbladder, pancreas, small intestine, and large intestine. These organs are responsible for transporting, breaking down, and extracting nutrients from food that the body can use for energy and for other metabolic processes. At the lower end of the digestive tract, the colon performs another function: the removal of undigested food waste and bile from the body. This is one example of the overlap in the relationship between the digestive system and excretory system. That is, even though this type of waste removal is considered a function of the digestive system, as the intestines are namely a digestive organ where nutrients are absorbed into the bloodstream and not strictly an organ of excretion like the kidneys, in this role they contribute to the excretory process.