Blood flow is the continuous circulation of blood in the cardiovascular system. This process ensures the transportation of nutrients, hormones, metabolic wastes, O2 and CO2 throughout the body to maintain cell-level metabolism, the regulation of the pH, osmotic pressure and temperature of the whole body, and the protection from microbial and mechanical harms. The science dedicated to describe the physics of blood flow is called hemodynamics. For the basic understanding it is important to be familiar with anatomy of the cardiovascular system and hydrodynamics. However it is crucial to mention that blood is not a Newtonian fluid, and blood vessels are not rigid tubes, so classic hydrodynamics is not capable of explaining hemodynamics.