An arteriole is a small blood vessel that forms a connection between small arteries and capillaries. Arterioles are an important part of the circulatory system. These vessels are filled with oxygenated blood from the heart that has a bright red appearance, in contrast with the blue tinge of blood being carried toward the heart and lungs so that it can be reoxygenated.
These blood vessels are between 10 and 100 micrometers wide, about the width of a human hair or smaller. They have thin muscular walls that can be contracted to restrict the flow of blood through a give arteriole or relaxed to increase the flow of blood. These vessels are supplied by small arteries, and small arteries in turn get their blood supply from the large arteries of the body. From the arteriole, blood passes into the capillaries. Pores in the walls of the capillaries allow for the exchange of nutrients and wastes that are carried away in the venules connected at the other side.
Arterioles play an important role in determining how much blood is distributed to organs and tissues. The body produces vasodilators and vasoconstrictors, compounds that dilate and contract blood vessels, to regulate the movement of blood through the circulatory system. Blood supply can be increased in situations like injuries where there is a need for ample blood, or restricted if the body wants to divert resources elsewhere. This also has an impact on blood pressure. When the blood vessels are relaxed, blood pressure is low because there is less resistance.
The circulatory system is a highly efficient and well-oiled machine. In addition to supplying nutrients and carrying away wastes, the blood is also involved in immune system functions and injury response. On very short notice, signals can be sent to redirect supplies of blood, increase a blood supply to a given area, or circumvent a blockage to deliver blood to an area of tissue that is at risk of ischemia, or lack of oxygen.
One problem that can develop within an arteriole is clotting, which leads to increased blood pressure in addition to restricting the supply of blood to an area fed by an obstructed vessel. Diseases involving the circulatory system can limit circulation or damage individual vessels, leading to tissue death and other problems. The microcirculation involving the arterioles, capillaries, and venules is critically important to the health of every part of the body from the skin to the spleen.