The principal function of the cardiovascular system is to transport oxygen and nutrients to the tissues and remove the products of cellular metabolism. This is achieved in two ways: by diffusion; by convection or bulk flow.

Diffusion, which is a random process, is extremely slow and a more efficient means of transport is needed for distances greater than 0.1 ^m.

Convection or bulk flow allows oxygen bound to hemoglobin to travel from the lungs to the most peripheral capillaries in about 30 s. Convection requires energy (a pump) and a complex system of conduits (the vascular tree). The heart is the pump or, rather, two pumps in series: the right atrium and ventricle provide the energy for convective transport to the lungs, and the left atrium and ventricle do the same for the systemic circulation. The function of the systemic circulation is to distribute cardiac output to all the tissues. Thus the cardiovascular system can be broken down into the pump function, i.e. the cardiac output, and regional blood flow.

In addition to its transport function, the cardiovascular system has a control or regulatory function. It provides the conduit for hormones to reach their target organs and it also regulates body temperature. We will not address these functions here, but will concentrate on the biomechanics of the pump function and the main principles of the circulation.

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