The difference between the blood vessels, arteries, veins and capillaries is in their shapes, sizes and function in the circulatory system.
Blood vessels as defined by the dictionary as tubular structures carrying blood to tissues and organs of the body. Blood facilitates the distribution of oxygen, chemicals, water and other important matters to all parts of the body as well as removes wastes.
There are three major types of blood vessels, and these are the arteries, veins and capillaries.
Arteries, except for the pulmonary artery, carry oxygenated blood away from the heart to the different parts of the body. Veins, except for the pulmonary vein, carry unoxygenated blood toward the heart. The pulmonary veins and arteries are responsible for bringing the blood to the lungs for oxygenation. Oxygen is an important element in the blood. Lack of oxygen in the brain cells will cause death. Capillaries are the smallest blood vessels that facilitate exchange with the tissues. Capillaries deliver oxygen, water, and nutrients in exchange for carbon dioxide and cellular waste matter in the tissues for disposal through the excretory system.
Structurally, arteries have three layers, the veins have two layers and the capillaries have only one layer of endothelium and some connective tissue. Arteries branch into smaller arteries and into capillaries. The smallest arteries are called arterioles while the smallest veins are called the venules. The capillaries are connected to the arterioles and venules. It is important for the capillaries to be thin and small to be able to transfer of nutrients and other matters.
Smooth blood flow is regulated by the autonomic nervous system.