Smooth muscle is a type of non-striated muscle, found within the tunica media layer of arteries and veins, the bladder, uterus, male and female reproductive tracts, gastrointestinal tract, respiratory tract, the ciliary muscle and iris of the eye. The glomeruli of the kidneys contain a smooth muscle-like cell called the mesangial cell. Smooth muscle is fundamentally different from skeletal muscle and cardiac muscle in terms of structure, function, excitation-coupling, and mechanism of contraction.