The cardiovascular system includes the heart, blood, and blood vessels (arteries, veins and capillaries).
Our blood circulates through this network of vessels throughout the whole organism. By this it can provide individual cells with oxygen and nutrients.
As the heart is powering a circulatory system, its pumping action also causes blood to return to the heart.
During this part of the journey, blood collects waste products, which are eliminated in the lungs. The lungs refresh the blood with oxygen and nutrients before it is returned to the heart to start the circulation process once again.
We have learned that our blood travels through the bloodstream - a system of blood vessels, or tubes, of varying sizes, which reach all parts of the organism. The tubes that carry blood away from our heart are called arteries, which carry blood pumped under high pressure to smaller and smaller branched tubes, called capillaries. Blood always leaves the heart through arteries, which include the aorta and pulmonary arteries. Conversely, blood enters the heart through the veins, the largest being the pulmonary veins and the vena cava.
Various control mechanisms help to regulate and integrate the miscellaneous functions and component parts of the cardiovascular system in order to supply blood to specific body areas according to need. These mechanisms ensure a perpetual internal environment surrounding each body cell regardless of differing demands for nutrients or production of waste products.