The heart, blood, and blood vessels form the basis of the cardiovascular system, also known as the circulatory system. The average human body contains around 5 liters of blood which is transported around the body through a network of blood vessels divided into three types; arteries, veins and capillaries. Arteries are the largest vessels and carry blood away from the heart. Veins carry blood to the heart and are smaller than arteries, then finally smaller vessels known as capillaries distribute the oxygen-rich blood to the organs and simultaneously collect waste carbon dioxide and water from the organs to transport them to the heart where it can be pumped into the lungs to be exhaled. Blood actually has multiple components: Red blood cells are the transport mechanism that carries vital materials such as nutrients and oxygen to the body's cells and removes waste and unused byproducts produced by organ and body function. Hemoglobin in the blood transports oxygen molecules around the circulatory system. Oxygen binds to iron in blood cells and gives blood its red color. When blood diffuses through the membranes of the capillary walls and into the cells of the organs, the level of carbon dioxide is diffused as waste from the cells to the blood cells where it can be transported to the excretory organs, as well as repeating. process of reoxygenation of pulmonary capillaries. Red blood cells are transported around blood vessels in a straw-like fluid called plasma. The blood also contains bacteria that fight white blood cells, which are fewer than red blood cells, but are larger in size. If the walls of the blood vessels are damaged, the platelets in the blood composition help to form a... paper center... opposite side. Blood enters the left atrium, passes through a valve and enters the left ventricle, is pumped through another valve and pumped out of the heart to the organs to transport oxygen and nutrients. Blood is pushed along the vascular network from the heart through arteries, veins and capillaries where oxygen- and nutrient-rich blood exchanges and collects deoxygenated blood and waste from organs. At this point the cycle returns to the pulmonary circulation and the entire process repeats. The cardiovascular system, while pumping oxygenated blood in and out of the heart, also transports nutrients and waste products from other parts of the body. The other systems of the body such as the digestive, respiratory and nervous systems are connected and function thanks to their connection with this circulation of the cardiovascular system.