Arteries - Circulation

The arteries deliver blood from the heart. Figure shows the structure of arteries and the different layers of the vessel wall. The thick walls of these blood vessels, except those of the smallest, are supplied by their own capillary network called vasa vasoram. The arteries serve four main functions:

1. To act as a conduit for blood between heart and capillaries,
2. To act as a pressure reservoir for forcing blood into small diameter arterioles,
3. To produce a more or less even flow of blood through the capillaries,
4. To control distribution of blood to different capillary networks via selective constriction of the terminal branches

Figure: Major structures in peripheral blood circulation in mammals. Blood flows from the arteries through the capillaries into the veins (id is internal diameter).

There is a precise control on arterial blood pressure. The nature of the arterial wall and the volume of blood pumped into the arteries determine the pressure. If any of these are changed, the pressure will also change. Normally, arterial blood pressure varies very little as cardiac output and capillary flow is evenly matched.

The elastic properties of arterial walls vary. Close to the heart the arteries are elastic and dampen the oscillations in pressure and flow generated by the contractions of the heart. As the heart relaxes the pressure in the arteries is maintained by a reduction in vessel volume. If the arteries were rigid tubes then the same pressure fluctuations would be experienced by peripheral vessels as that observed when blood leaves the heart.