In general, arteries get smaller as they get further away from the heart. When they have decreased in size to a certain point, they are then referred to as arterioles.
Arterioles share many of the properties of arteries they are strong, have a relatively thick wall for their size, and contain a high percentage of smooth muscle.
Just like arteries, arterioles carry blood away from the heart and out to the tissues of the body. In addition to this "supply train" function, arterioles are very important in blood pressure regulation.
Arterioles are very important because, as a group, they are the most highly regulated blood vessels in the body, and contribute the most to overall blood pressure. Arterioles respond to a wide variety of chemical and electrical messages and are constantly changing size to speed up or slow down blood flow.
Continue Reading: Part Four: Capillaries