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 to the blue tint of blood that is carried to the heart and lungs so 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 contract to restrict blood flow through a given arteriole or relax to increase blood flow. The arteries are supplied by small arteries, and the small arteries in turn get their blood supply from the large arteries of the body. From the arteriole, the blood passes into the capillaries. Pores in the walls of the capillaries allow for the exchange of nutrients and wastes that are carried into the connected venules on 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 constrict blood vessels, to regulate the movement of blood through the circulatory system. The blood supply can be increased in situations such as injuries where there is a need for a large amount of blood, or restricted if the body wants to divert resources elsewhere. This also has an impact on blood pressure. When arterioles 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 transporting waste, blood is also involved in immune system functions and response to injury. In a very short time, signals can be sent to redirect blood supplies, increase blood supply to a certain area, or bypass a blockage to bring 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, as well as restricting blood supply to an area fed by a clogged arteriole. Diseases involving the circulatory system can limit circulation or damage individual arterioles, leading to tissue death and other problems. Microcirculation involving arterioles, capillaries, and venules is vitally important to the health of every part of the body, from the skin to the spleen.