The circulatory system is the process in the human body where the blood is cycled through the blood vessels, the heart and the lungs. The circulation keeps the tissue in the body full of oxygen, which is used for energy in cellular respiration. Without oxygen, the body is unable to produce adenosine triphosphate (ATP), which is the body's energy form.
All oxygen and nutrients that move using the circulatory system are contained in the blood. The blood is composed mainly of white blood cells, red blood cells and platelets. The red blood cells are responsible for carrying oxygen. White blood cells are the main structures of the immune system. Platelets are responsible for coagulation when tissue damage occurs.
The heart is a muscle that creates a pressure in the circulatory system to cycle blood to and from the tissue. The heart consists of two ventricles, two atria and valves that open and close while the blood circulates. The heart is also responsible for circulating blood to and from the lungs, which is where it binds to oxygen and removes carbon dioxide.
The vessels are the medium in which blood travels. The vessels are composed of arteries, arterioles, capillaries and veins. These vessels branch out as large diameter structures from the heart to small vessels such as capillaries. Capillaries are the smallest blood vessels and are the site of oxygen and carbon dioxide exchange in cells.
Lungs fill with oxygen when a person inhales. Oxygen moves to the bronchioles and alveoli where gas exchange occurs with red blood cells. Red blood cells adhere to the oxygen molecules in the alveoli when a person inhales. When a person exhales, the carbon dioxide that was in the blood is sent to the alveoli and then sent out of the body through the mouth.
The path of the circulatory system starts at the heart in this example. The circulatory system is a cycle, so there is no starting or ending point. Rather, the blood is transported in a cycle through the body. The heart pumps the deoxygenated blood from the right ventricle to the lungs. The red blood cells collect oxygen where they are sent back to the left ventricle of the heart. The left ventricle contracts and blood is pushed into the arteries. The arteries branch into smaller units called capillaries, where oxygen is left in the cells. The deoxygenated blood is transferred to the veins and poured into the right ventricle.This is the complete route of blood used by the circulatory system.