Describe the characteristic lesions of atherosclerosis.

Fatty streak: Lipid accumulation within the tunica intima leads to the formation of elevated linear lesions.
Fibrous plaque: Accumulation of smooth muscle cells and lipid-filled macrophages leads to the development of a central atheroma.
Complicated plaque: A fibrous plaque undergoes calcication, ulceration, hemorrhage, or necrosis and becomes susceptible to thrombosis.