The Circulatory System   Blood is the vital fluid of our organism, as it carries the nutritional elements which are necessary to the right functioning of our organs. A system made of a pump, our heart, and of ducts, our arteries, ensures its distribution throughout our body. The heart furnishes in a periodical manner, the energy required so blood can irrigate our whole body. The sending network is made of vessels of two types: distribution is completed by wide arteries (aorta, iliac arteries or carotid), while organs' perfusion is guaranteed by arteries of a smaller diameter (coronary, renal, mesenteric arteries) which ramify into ducts of decreasing thickness (capilar ducts), where the feeding exchanges blood/tissues take place. Arteries of the first type -elastic- have the peculiar property of perpetuating the pulsatory character of the flow, by stocking mechanical energy during systole, and retrieving it back nest during diastole, allowing a continuous perfusion towards arteries of the second type -muscular and resistive-. As a summary, the essential characteristics of the circulatory mechanics are therefore: the pulsatory character of the blood flow, the distensibility of the vessels, the variability of the mechanical and hydrodynamic properties under nervous or humorous action.