[1] Arterioles have muscular walls (usually only one to two layers of smooth muscle cells) and are the primary site of vascular resistance.

[2] In a healthy vascular system, the endothelium lines all blood-contacting surfaces, including arteries, arterioles, veins, venules, capillaries, and heart chambers.

In addition, there is direct electrical and chemical communication via gap junctions between the endothelial cells and the vascular smooth muscle.

Arterioles receive autonomic nervous system innervation and respond to various circulating hormones in order to regulate their diameter.

[4] Generally, norepinephrine and epinephrine (hormones produced by sympathetic nerves and the adrenal gland medulla) are vasoconstrictive acting on alpha 1-adrenergic receptors.

Generally, stretch and high oxygen tension increase tone, and carbon dioxide and low pH promote vasodilation.