Physical Characteristics of the Circulation The circulation, shown in Figure 14-1, is
divided into the systemic circulation and the pulmonary circulation. Because the systemic circulation
supplies blood flow to all the tissues of the body except the lungs, it is also called the greater circulation or peripheral circulation. Functional Parts of the Circulation. Before discussing the details of circulatory function, it
is important to understand the role of each part of the circulation. The function of the arteries is to
transport blood under high pressure to the tissues. For this reason, the arteries have strong vascular
walls, and blood flows at a highvelocity in the arteries. The arterioles are the last small branches of
the arterial system; they act as control conduits through which blood is released into the capillaries.
Arterioles have strong muscular walls that can close the arterioles completely or can, by relaxing,
dilate the vessels severalfold, thus having the capability of vastly altering blood flow in each tissue in
response to its needs.
