Circulation is the transport mechanism that involves the whole body, from the largest vessels to the smallest. The capillary level is where it is crucial to maintain the exchange of nutrients and oxygen and the removal of metabolic waste products such as carbon dioxide, which accumulates because of normal cellular function. There is a huge network of extremely small blood vessels in our body, some of which are four times thinner than a strand of hair. These networks of small vessels surround all organs and tissues in the body and are vital to cellular function.