The vascular system is one of the first developments in an embryo because transporting fluids is a fundamental need of growing life forms. As components of the vascular system, arterioles are small tubes that branch from arteries and are important in the conveyance of blood.

Arterioles vary in size, gradually becoming smaller and smaller as they move further away from the artery from which they extend. The largest arterioles consist of three layers, which become increasingly thinner and less discrete as the vessel decreases in size. By the time they reach the capillaries, the arterioles are little more than a thin lining encircled by a layer of muscle fibers.

Providing considerable resistance to blood flow because of their small diameter, arterioles help steady the pulsating flow from the heart before emptying into capillaries. The small vessels are also of great consequence in the determination of which tissues and regions of the body receive the greatest supply of blood. The muscular wall of the arterioles is strong enough to completely close off the vessel, as well as to expand itself to a significantly larger size. Such capabilities enable the arterioles to adjust blood flow based on bodily needs.