Circulating blood: What is it?

      In order to understand the 'why', we must first understand what blood is and how it operates. Circulating blood comes from the circulatory system in our bodies. The circulatory, or cardiovascular system, supplies oxygen and nutrients to our bodies while removing waste through blood. The heart is the major organ in the system, and pumps blood that flows through the arteries, veins, and capillaries. This back-and-forth transport is what carries oxygen-rich blood across tissues and oxygen-poor blood back to the lungs. There are two main circulatory routes: pulmonary and systemic. Pulmonary circulation focuses on creating a closed circuit between the heart and the lungs. Systemic circulation moves oxygenated blood into tissues and deoxygenated blood away from tissues.       Blood is more than a liquid     What's most fascinating about blood is that even though most tissues are packed tightly together in solid forms, blood is consi...