Digestion and excretion are usually treated as a single system, since these two components are continuous; first we digest nutrients and then we excrete what ever was not used. In addition, we can imagine our bodies as a long cylinder (or a donut) where the hole in the middle would be the digestive and excretory systems. The upper portion of the digestive tract is responsible for digestion, and the lower portion is responsible for excretion.
Diagram of different parts of the digestive system.
The role of the digestive system is to digest, breaking down food and delivering water, minerals, vitamins and all nutrients to the blood stream which will distribute them to all the cells of our body. The excretory system, in turn, serves to eliminate anything and everything that is not useful to our body. Another portion of the excretory system includes the kidneys. The kidneys are not shown in the figure, but they constitute an important part of the excretory system. They are used to purify the blood and eliminate organic waste into the urine. They are also very important for the balance water and minerals.
