The vascular system also referred to as the circulatory system or vascular tree carries blood, oxygen and essential elements to all metabolically active tissues and organs of the body and carries waste materials and by-products away. There are five distinct components of the circulatory system: arteries and arterioles (arterial system), veins and venules (venous system) and capillaries (microvascular system) that link arterioles and venules. The dimensions of blood vessels vary by an order of several thousand-fold with capillaries as small as 10 µm to the aorta of 25 mm (Fig. 1).
Fig. 1 The circulatory system consists of the heart and large, medium and small arteries (arterioles), capillaries, small veins (venules, sinusoids) and large veins. Normal function depends on the flow of blood (and nutrients) to and from vital organs; however, the microvessels (arterioles, capillaries and venules) are responsible for vascular tone, homeostasis and tissue perfusion. From