Arterioles are small diameter blood vessel that branches out from arteries and leads to capillaries.
Their wall consists of endothelial cells, an internal elastic lamina apposed by one or two layers of smooth muscle, and a thin layer of collagen fibers.
The inner elastic lamina is usually absent from smaller arterioles.
The thickness of vessel wall is usually similar in size to the diameter of the lumen.
Arterioles are the primary site of vascular resistance.