Tubes of various calibers for blood transport from or to the heart and the various organs of the body.
There are arterial and venous blood vessels. As a rule, the arterial system carries oxygen-rich blood to various body organs and the venous system is a draining system carrying low oxygenated blood from the organs back to the heart and from there to the lungs for oxygenation.
An exception thereof are pulmonary vessels, in which oxygen-low blood is, on the contrary, transported by arteries (branches of the pulmonary artery) and oxygen-rich blood is transported back to the heart by pulmonary veins.
Veins and arteries differ not only by their purpose and function, but also by their anatomical structure.
Arteries are more elastic and possess a muscular layer, thus being able to contract and expand.